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SINH HC I CNG

HU - 2006

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SINH HC T BO-----------------------------------------------------------------------------------------------------------------

Chng 1.

Cu trc ca t boI. i cng v t bo1. Lch s pht hin t bo Lch s pht hin t bo gn nh l lch s pht minh ra knh hin vi. Galileo (1564 1642) tnh c khm ph ra nhng vt rt nh khi quan st bu tri bng cch lt ngc u knh li. Antoni Van Leeuwenhoek (1632 - 1723) ngi H Lan, do yu cu kim tra t la, ng mi cc thu knh quan st cht lng ca vi, nh quan st c nhng vt li ti quanh mi trng sng v khm ph ra s hin din ca th gii vi sinh vt. Robert Hooke (1635 - 1703) ngi Anh, ln u tin m t cc l nh c vch bao bc ca ming bc (nt bn) ct ngang di knh hin vi nm 1665 v Hooke dng thut ng t bo (cellula) c ngha l phng, bung nh, v ngha lch s t ny vn cn c dng cho n ngy nay ch cc l . 2. Thuyt t bo Mi n th k 19 khi nim sinh vt c cu to t bo ca Hooke mi c ch t nhiu cng trnh nghin cu. Nh thc vt hc Matthias Jakob Schleiden (1838) v nh ng vt hc Theodor Schwann (1839) ngi c h thng ha quan im thnh thuyt t bo. Tt c cc sinh vt do mt hay nhiu t bo to thnh, hay t bo l n v cu to sng c bn ca tt c sinh vt. n nm 1858 thuyt t bo c Rudolph Virchow m rng thm: T bo do t bo c trc sinh ra. Quan im ny sau c L. Pasteur (1862) chng minh. Nh vy c th tm tt thuyt t bo nh sau: T bo l n v cu to sng c bn ca tt c sinh vt, t bo do t bo c trc sinh ra. 3. Hnh dng v kch thc t bo 3.1 Hnh dng Hnh dng ca t bo rt thay i v ty thuc rt nhiu vo tnhchuyn ha ca chng (nh sinh vt a bo mt loi t bo gi mt nhim v no trong c th). T nhng dng n gin nh hnh cu, hnh trng, hnh que c th gp cc sinh vt n bo n nhng hnh dng phc tp nh cc t bo hnh sao m thc vt, hay cc t bo thn kinh ng vt cp cao... cc sinh vt n bo hnh dng c ngha quan trng i vi i sng ca chng. Th d, vi khun hnh cu c th chu ng c s kh hn gii v din tch tip xc vi mi trng bn ngoi t do gi c nc d mi trng sng rt kh. 3.2 Kch thc Kch thc ca t bo cng rt thay i theo loi t bo. Ni chung, thng t bo rt nh v phi dng knh hin vi mi quan st c. Th d, vi khun Dialister pneumosintes c kch thc rt nh 0,5 x 0,5 x 1,5m trong khi trng ca chim iu l t bo c ng knh n 20cm, hay t bo thn kinh c ng knh nh nhng c th di n 90 - 120cm. Tht ra ln nh ca t bo khng quan trng m t l gia din tch b mt v th tch t bo mi c nh hng ln n i sng ca mt t bo. T bo ly thc n, oxy t mi trng chung quanh v thi cht cn b ra bn ngoi t bo. Cc vt liu ny u phi di chuyn xuyn qua b mt ca t bo. Khi t bo gia tng kch thc, th tch tng gp nhiu ln so vi s gia tng ca din tch ( hnh cu, th tch tng theo ly tha bc ba trong khi



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din tch tng theo ly tha bc hai). Do , khi t bo cng ln ln th s trao i qua b mt t bo cng kh khn hn 4. Phn loi t bo C th phn chia t bo ra lm hai nhm: t bo tin nhn v t bo nhn tht. T bo tin nhn (prokaryote) l loi t bo khng c mng nhn, ADN c cu trc xon vng kn, khng c cc bo quan c mng. Cc t bo ny gp cc sinh vt thuc gii sinh vt tin nhn: Archaebacteria v Eubacteria. T bo nhn tht (Eukaryote) l loi t bo c nhn vi mng nhn bao quanh, v nhiu loi bo quan c mng bao. Cc t bo ny gp cc sinh vt thuc cc gii Protista, Nm, Thc vt v ng vt.

II. Cu trc ca t bo tin nhnTrong t bo tin nhn khng c mng nhn v cng khng c cc cu trc c mng khc nh mng ni cht, h Golgi, tiu th, peroxisom v ty th (cc chc nng ca ty th c thc hin mt trong mng ca t bo vi khun). cc vi khun quang tng hp, c nhng phin hay ti c cha dip lc t m khng phi l cc lp c mng bao ring bit (hnh 1.1). Hin nay, vi knh hin vi 2 3 in t ngi ta bit rng mi t bo tin nhn c mt phn t ADN 1 to, mc d n khng lin kt cht ch vi protein nh ADN t bo 4 nhn tht, n vn c xem l nhim sc th. T bo vi khun hng c cc ADN nh, c lp c gi l 5 plasmid. Nhim sc th ca t bo 6 tin nhn v plasmid c kin trc 7 vng kn. Nhim sc th ca t bo tin nhn c mang cc gen kim Hnh 1.1 Cu to mt t bo vi khun sot cc c im di truyn ca t 1. Th rib; 2. Lng nh; 3. ADN; 4. Roi; 5. V bc; 6. Vch t bo; 7. Mng t bo bo v cc hot ng thng thng ca n. S tng hp protein c thc hin trn th rib, mt bo quan quan trng trong t bo cht c t bo tin nhn v nhn tht. Tuy nhin, th rib ca t bo tin nhn hi nh hn ca t bo nhn tht. Mt s t bo vi khun c t m quen gi l roi (chin mao). Nhng roi ny khng c vi ng v cu trc cng nh s c ng hon ton khc roi ca t bo nhn tht. Roi ca vi khun ch c cu to bi mt loi protein c tn l flagellin xp theo ng xon. S c ng ca vi khun l do s quay trn ca cc si protein ny v y t bo i ti, s i hng di chuyn l nh s o ngc chiu quay mt cch tm thi ca cc si protein ca roi (hnh 1.2). Vch t bo ca hu ht vi khun c cu to bi murein gm mt ng a lin kt vi cc nhnh acid amin.

III. Cu trc ca t bo nhn thtT bo c mt mng bao bc gi l mng t bo, bn trong mng l cht nguyn sinh (protoplasm), gm t bo cht (cytoplasm), nhn v cc bo quan (organelle) khc. Cu trc t bo ca c th ng vt v thc vt c khc nhau (hnh 1.3).



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vch ca vi khun

m t quay

flagellin

bao roi

Hnh 1.2 Chuyn ng roi ca vi khun a) nh chp loi Vibrio chlorae; b) Chi tit ca roi Vibrio; c) Kiu xoay trn ca roi Vibrio

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1 2

15 14 3 13 12 4 5 11 10 5 9 6 7 8 7 1 2 3 4

13 12

11 10

6

9

8

B

A

Hnh 1.3 Cu to t bo thc vt (A) v t bo ng vt (B) A. 1. Lc lp; 2. Si lin bo (cu sinh cht) ; 3. Th lyso (tiu th) ; 4. Mng nhn; 5. Li ni cht ht; 6. T bo cht; 7. Li ni cht trn; 8. Hch nhn; 9. Nhn; 10. B my golgi; 11. Th rib; 12. Ty th; 13. Khng bo, 14. Mng t bo; 15. Vch t bo B. 1. Vi t; 2. Mng t bo; 3. Trung th; 4. Th lyso (tiu th); 5. Th rib; 6. Ty th; 7. Li ni cht ht; 8. T bo cht; 9. Nhn; 10. Hch nhn; 11. Mng nhn; 12. Li ni cht trn; 13. Xng t bo cht; 14. B my golgi

1. Cc bo quan 1.1 Mng ni cht (ER) c pht hin vo nm 1945 nh knh hin vi tng phn pha (phase-contrast



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microscope), tt c t bo nhn tht. Knh hin vi in t cho thy mng ni cht ni lin vi mng ngoi ca nhn mt s v tr. Mng ni cht ging nh mt h thng ng v ti, trn hay dp, thng thng vi nhau v c mng bao quanh (cisternae). Khong gia hai mng ca ti, ng c gi l khoang (lumen). hu ht t bo, mt ngoi ca mng ni cht c cc th rib gn vo, khi n c gi l mng ni cht ht (RER), ni khng c cc th rib c gi l mng ni cht trn (SER) (hnh 1.4).

Th rib

li ni cht ht

A

li ni cht trn

BHnh 1.4 Mng ni cht ca t bo ng vt A. t bo ng vt; B. Li ni cht nhn tng qut; C. Cu to chi tit

C

Khoang (lumen) ca mng ni cht lin h trc tip vi vng ngoi vi ca mng nhn. Do , nhng knh trn mng ni cht c th l con ng vn chuyn vt cht gia nhn v nhng phn khc ca t bo cht, to ra mt h thng thng tin gia nhn l trung tm iu khin v phn cn li ca t bo. Hu ht protein lin kt vi mng hay c vn chuyn bi mng ni cht c tng hp bi th rib ca mng ni cht ht. Protein tng hp t cc th rib t do trong t bo cht s thc hin chc nng trong dch t bo cht. Ngoi nhim v l ng vn chuyn bn trong t bo, mng ca mng ni cht l ni cha cc protein v cc protein ny c c hai chc nng, va l thnh phn cu trc va l enzim xc tc cc phn ng ha hc. Hin nay, c nhiu bng chng cho thy rng t nht l mt s protein cu to mng ni cht hot ng nh enzim; mt s ca nhng enzim ny c gn thm mt ng a mch ngn. ng ny c nhim v nh mt ci nhn a th (mailing label) a protein n ng ni nhn trong t bo (hnh 1.5). Trong hnh 1.5 mt chui gm 14 phn t ng gn vo phn t protein trn mng ni cht ht c chc nng nh mt ci nhn, protein no khng c nhn th s li mng ni cht. Khi bn phn t ng cui cng c tch ra th protein s c chuyn n h Golgi (G: glucoz, M: manoz, N: N-acetyl-glucosamin). Mng ni cht cn c nhim v nh mt xng ch to, cc enzim ca chng xc tc s tng hp cc phospholipid v cholesterol c dng to ra mng mi hay cc protein mng c tng hp bi th rib trn mng ni cht l thnh phn ca mng lipid mi. Vng trn c bit gia tng cc t bo c nhim v tng hp lipid nh hormon steroid. t bo gan ca ng vt c xng sng, protein mng ca vng trn c vai tr quyt nh trong s thi cht c dc phm nh thuc gim au, thuc kch thch (camphetamin, morphin v codein)...



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1.2 H Golgi Khoang Camillo Golgi l ngi u tin m t vo nm 1898, h golgi gm mt h thng ti dp c mng bao v xp gn nh song song nhau. Mt pha gn nhn c gi Nhn gn l mt cis, pha i din l mt trans. Cc ti chuyn ch cha bn Polypeptid trong lipid v protein mi c Th rib tng hp, c tch ra t mng Mng ca li ni cht ca mng ni cht ha vo cc ti dp ca h Golgi mt cis. Cc cht ny vo trong h Golgi c Hnh 1.5 S gn nhn trn mng ni cht bin i, sp xp li hnh thnh cc ti mi c tch ra t mt trans sau vn chuyn cc phn t n cc bo quan khc v mng sinh cht, i khi cc ti c chuyn n glycocalyx. H Golgi c bit to nhng t bo tit nh t bo ty tng tit ra insulin hay t bo rut non tit ra cht nhy. Hin nay, ngi ta bit vai tr ca h Golgi l tn tr, bin i (c c li) v bc cc sn phm tit li. Mc d s tng hp protein khng xy ra h Golgi, nhng nhng ng a c tng hp ti y t cc ng n s c gn vo lipid hay protein to ra glycolipid hay glycoprotein. Cc ti c tch ra t h Golgi c vai tr quan trng lm tng b mt ca mng t bo. Khi ti c chuyn n b mt ca mng sinh cht, chng s c gn vo mng ny, sau v ra v phng thch cht ra bn ngoi t bo trong qu trnh ngoi xut bo, mt phn hay tt c mng ca ti c ha vo mng sinh cht hay tr v h Golgi. Cc kt qu nghin cu cho thy c s lin quan gia nhng phn khc nhau ca tng th h thng mng trong t bo. Mt phn t cu trc mng c ngun gc t vng ht ca mng ni cht c chuyn n vng trn, sau i n h Golgi trong cc ti chuyn ch v cui cng n mng sinh cht, t y chng c th tr v h Golgi hay mt s bo quan khc ch l mt ti rng. Nh vy mng phospholipid lun c i mi (hnh 1.6).

Ti tit

A

B

T bo cht

Ti

CHnh 1.6 Th golgi ca t bo ng vt: A. T bo ng vt; B. Cu to tng qut h Golgi; C. Cu to chi tit h Golgi.

1.3 Tiu th (lysosome) L nhng ti d tr cc enzim tiu ha c kh nng thy phn cc i phn t trong t bo. Tiu th l mt th c mng bao bc, l mng khng thm. Nu mng ca tiu th b v



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ra, cc enzim c phng thch vo trong t bo cht v lp tc cc i phn t trong t bo s b phn gii v vy tiu th hot ng nh mt h thng tiu ha ca t bo, c kh nng tiu ha cc vt liu c kch thc ln c mang vo t bo do s ni nhp bo. Enzim tiu ha c tng hp vng ht ca mng ni cht, c bc li vng trn trong cc ti chuyn ch v c chuyn n h Golgi. Khi c mt ni no cn enzim th t mng ca h Golgi tch ra mt ti c cha enzim. Nhng protein gn bn ngoi ca tiu th nh l mt b phn nhn din ra rng enzim n ng v tr cn n, th d ni c cc ti ni nhp bo t mng t bo a vo, ti y tiu th v ti ny s ha vo nhau. Khi ni dung c tiu ha hon ton, nhng sn phm hu ch c a tr vo t bo cht, nhng cn b c a ra ngoi bi s ngoi xut bo, mng ca ti c ha nhp vo mng t bo (hnh 1.7). S hot ng khng bnh thng ca tiu th l nguyn nhn ca nhiu bnh. Mt trng hp c bit l bnh Tay - Sachs, v tiu th tiu ha lipid thiu mt enzim. Khi nhng tiu th thiu enzim ny ha vo nhng ti cha lipid, chng khng tiu ha hon ton c lipid ny. Nhng ti ny tch t v lm nghn s dn truyn cc xung ng ca cc t bo thn kinh.T bo cht Thc bo ti thc n H golgi Li ni cht

Th lyso

Ti chuyn C quan t c C quan t c b b gy

Mng t bo Dch ngoi t bo

S tiu ho thc bo

Hnh 1.7 S tiu ho ni bo c s tham gia ca tiu th

1.4 Peroxisom Peroxisom c sinh ra t peroxisom c trc. T bo phi c tha hng t nht mt peroxisom t t bo cht ca t bo m. C hnh dng tng t nh tiu th, peroxisom cha enzim nhng l enzim oxy ha, chng xc tc cc phn ng trong nguyn t hydro c chuyn t hp cht hu c (nh formaldehyd v ru ethyl) n oxy, to ra hydro peroxyd (H2O2), l mt cht cc c i vi t bo. Tuy nhin, peroxisom cn c mt enzim khc na l catalaz, s chuyn cht H2O2 c ny thnh nc v oxy. T bo gan v thn ngi c rt nhiu peroxisom, do ru ethyl do ngi ung c oxy ha nh cc peroxisom trong nhng t bo ny. 1.5 Khng bo c tm thy c t bo thc vt v ng vt, c bit rt pht trin t bo thc vt. C mt mng bao quanh, bn trong cha mt dch lng, vi nhiu loi khng bo khc nhau v chc nng. mt s ng vt nguyn sinh, c khng bo c bit gi l khng bo co bp (contractile vacuole) gi vai tr quan trng trong s thi nc ra khi t bo hay cc khng bo tiu ha tiu ha thc n. Ngoi ra, vi khun v vi khun lam c khng bo kh cha kh gip t bo ni ln mt nc v im c bit l mng bao ca khng bo kh c cu to bng protein.



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hu ht t bo thc vt, c mt khng bo rt to chim t 30 - 90% th tch t bo. Cc t bo cha trng thnh c nhiu khng bo nh xut x t mng ni cht v h Golgi. Cc ti ny tch cha nc, to ra v c th ha vo nhau to ra mt khng bo to t bo trng thnh. Khng bo t bo thc vt cha mt dch lng gm nc v mt s cht ha tan trong (hnh 1.8). Mng khng bo c tnh thm c bit v c th iu khin s di chuyn vt cht qua mng ny. Khng bo tch nc bng s thm thu, trng ln v y t bo cht ra st vch t bo, p lc ny to cho t bo mt sc trng nht nh. Vch t bo cng rn gi cho t bo khng b v ra. Sc trng ca t bo rt quan trng, n gip cho cc c quan ca cy nh l, thn non ng vng c. Khi sc trng ny khng cn na, cy s ho. Nhiu cht quan trng cho i sng ca thc vt c cha trong khng bo: cc hp cht hu c nh ng, cc acid hu c, acid amin, mt vi protein, sc t antocianin cho mu tm, xanh v m thng thy trong cnh hoa, tri v l vo ma thu. p sut thm thu cao ca khng bo gip cho cy c th hp thu c nc t rt kh bng s thm thu. Ngoi ra, khng bo cn l ni tch cha nhng cht thi do cc qu trnh bin dng. Mt s cht thi c th c s dng li di tc dng ca enzim. Chc nng ny rt quan trng v cy khng c thn hay cc c quan khc thi cht b nh ng vt, thc vt thi cht b khi rng l.Hnh thnh khng bo

Hnh 1.8 S hnh thnh khng bo thc vt

1.6 Ty th Ty th l ni tng hp nng lng ch yu ca t bo nhn tht, l ni din ra qu trnh h hp, ly nng lng t thc n tng hp ATP l ngun nng lng cn thit cho cc hot ng ca t bo nh co c hay cung cp cho cc bm hot ng trong s vn chuyn tch cc qua mng t bo. S lng ty th ty thuc vo mc hot ng ca t bo. Th d, t bo c tim nu co tht 72 ln trong mt pht th c cha hng ngn ty th. Ging nh nhn, mi ty th c bao bc bi hai mng, mng ngoi trn, mng trong vi cc ti gp np, su vo bn trong cht cn bn lm gia tng din tch ca mng trong ln rt nhiu. Ty th c cha ADN, th rib ring nn c th nhn ln c lp vi s phn chia ca nhn (hnh 1.9). 1.7 Lp th c tm thy trong hu ht t bo thc vt, tr t bo nm, mc v t bo ng vt, c th quan st c di knh hin vi thng. C hai loi lp chnh l sc lp v v sc lp. a. Lc lp (chloroplast): Lc lp l sc lp c cha dip lc t (chlorophyll), v cc sc t vng hay cam gi l carotenoid. Phn t dip lc t hp thu nng lng nh sng mt tri



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tng hp ra cc phn t hu c phc tp (c bit l ng) t cc nguyn liu v c nh nc v kh carbonic, cht thi ra l xy.

5 4 1 2 3

A BHnh 1.9 Cu to ty th: A. T bo; B. Ty th 1. Khong trng bn trong; 2. Tm lc; 3. Cht nn; 4. Mng trong; 5. Mng ngoi

Di knh hin vi in t, mt lc lp c bao bc bi hai mng v v s cc ti dp c mng bao c gi l thylakoid nm trong cht c bn gn nh ng nht c gi l stroma. Thylakoid hoc phn b khp trong stroma, hoc xp chng cht ln nhau c gi l grana (ct). Dip lc t v carotenoid gn trn mng thylakoid. Lc lp cng c cha ADN v th rib ring nh ty th (hnh 1.10). B. Sc lp khng c dip lc t: Thng c mu vng hay cam (i khi c mu ) v chng cha carotenoid. Sc lp ny lm cho hoa, tri chn, l vng c mu vng c trng. Mt s sc lp khng bao gi cha dip lc t, mt s khc th mt dip lc t, y l trng hp ca tri chn v l ma thu.1 2 3 4 5

A

B CHnh 1.10 Cu to lc lp A. T bo thc vt; B. Cu to mt lc lp; C. nh hin vi in t lc lp 1. Mng ngoi; 2. Mmg trong; 3. Ct; 4. Ti dp (thylakoid); 5. Cht nn

c. V sc lp: V sc lp c cha cc vt liu nh tinh bt, du v protein d tr. Lp c cha tinh bt c gi l bt lp, thng gp ht nh la v bp, hay d tr trong r v thn nh carot v khoai ty, ngoi ra c th hin din trong t bo cc phn khc ca cy. Tinh bt l hp cht d tr nng lng di dng tng ht. Cy c ht giu tinh bt l ngun lng thc giu nng lng. 1.8 Th rib



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Th rib l nhng ht nh khng c mng bao c ng knh t 25 - 30nm, trong t bo cht cha vi triu th rib. Th rib gm hai bn n v (phn) c to ra trong hch nhn t nhng phn t ARN v protein. t bo nhn tht cc bn n v ny i qua l ca mng nhn ra ngoi t bo cht, ni y chng s kt hp vi phn t mARN tng hp protein. Th rib trc dc theo si mARN to ra mt chui th rib c gi l polyribosom hay polysom, cc th rib sau khi tng hp protein vn tip tc t do trong t bo cht hay chng c th gn vo b mt ca mng ni cht. Chng c th gn trn vng ht ca mng ni cht hay tri ni trong t bo cht. Protein c tng hp t cc th rib t do trong t bo cht th khng c a ra khi t bo hay tham gia vo cu trc mng t bo m l nhng enzim trong dch t bo cht (hnh 1.11). 1 3.9 Trung th t bo ng vt, bn ngoi nhn c mt vng c gi l trung th bao gm hai bo quan c gi l trung t (centriole). Trung t 2 hin din tng i v xp thng gc nhau. Khi c trung t chng l ni xut pht ca thoi vi ng trong lc t bo phn ct. tit din ngang, 3 trung t c cu trc ng u vi chn nhm ba vi ng xp thnh ng trn (hnh 1.12). Hnh 1.11 Th rib 1. Bn phn I; 2. Bn phn II; 3. Th rib Th gc c cu to ging ht trung t, c tm thy gc ca cc tim mao v roi. Trung t v th gc c mi lin quan vi nhau. Th d, th gc roi ca nhiu loi tinh trng tr thnh mt trung t ca t bo trng sau khi th tinh, trung t ca t bo thnh ca ng dn trng phn ct thnh th gc tim mao hot ng nhp nhng a trng n ni th tinh. 2. Nhn (nucleus) Nhn ng vai tr quan trng trong s sinh sn ca t bo, l trung tm ca mi hot ng ca t bo v cn c vai tr quan trng trong vic xc nh cc c im di truyn. Nhn cha hai cu trc phn bit c l nhim sc th v hch nhn. Di knh hin vi in t, c th thy c hai cu trc ny nm trong mt B ba vi ng khi cht v nh hnh c dng ht, c gi l cht nhn. Nhn c bao bc bi mng nhn gm hai mng phn bit c. 2.1 Nhim sc th Hnh si di, gm ADN v protein, quan st c r rng trong lc t bo ang phn Hnh 1.12 Cu to trung th chia. ADN l vt liu cha cc n v c bn a). nh hin vi in t thy c cc cp trung th (x 75.000) ca s di truyn c gi l gen, protein lm b). Mi trung t gm 9 b ba vi ng thnh nhng phn li ging nh nhng cun ch, si ADN qun ln , to nn cu trc th nhn (hnh 1.13 v 1.14). Gen c sao chp khi t bo phn ct mi t bo con u c mt bn sao. Tt c gen trong t bo c gi l b gen. Gen c xem l trung tm ca s sng, chng m ha cc thng tin cn thit cho s tng hp cc enzim, iu ha v s cc phn ng ha hc tiu biu ca t bo v ca sinh



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vt. Thng tin di truyn mang bi cc gen l trnh t cc nucleotid, ca phn t ADN. Trnh t ny xc nh trnh t ca acid amin trong phn t protein c tng hp trong t bo cht. 2.2 Mng nhn Mng nhn ngn cch mi trng bn trong nhn v t bo cht bao quanh, l ni cho hai u nhim sc th bm vo. Mng nhn gm hai mng, mng ngoi v mng trong, khong ngn cch gia hai mng l vng ngoi vi. Di knh hin vi in t hai mng ca mng nhn c ngt qung bi cc l, mi l nhn c vin bi mt phc hp gm tm protein. Mng nhn c tnh thm chn lc cao. S trao i cht xuyn qua cc l c kim sot nghim ngt v c tnh chn lc rt cao. Nhiu nghin cu cho thy mt s phn t c th i xuyn qua mng sinh cht vo t bo cht, nhng li khng th xuyn qua mng nhn vo nhn, ngay c nhng phn t c kch thc nh hn l nhn, trong khi c nhng phn t ln hn l nhn li c th i qua c (hnh 1.15).1

3 4 5

2

Hnh 1.13 Th nhn 1. Nhim sc th; 2. Th nhn; 3. DNA; 4 Histon trung tm; 5. Histon trng.

Hnh 1.14 Nhim sc th ca t bo nhn tht (x 500)

Hnh 1.15 Mng nhn



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2.3 Hch nhn Hch nhn thng c thy r nht lc t bo khng phn chia. Nhn cha mt n nhiu hch nhn. L mt phn ca nhim sc th nn hch nhn cng gm ADN v protein. ADN ca hch nhn gm nhiu bn sao ca gen lm khun tng hp rARN cho th rib. Sau khi c tng hp, rARN kt hp vi protein ri ri khi hch nhn v i ra t bo cht, ni y chng tr thnh mt thnh phn ca th rib. Do vy, khi t bo t tng hp protein hch nhn rt nh hay gn nh vng mt. 3. T bo cht T bo cht l thnh phn ca cht nguyn sinh gm phn dch lng l dch t bo cht v b khung protein c gi l khung xng t bo. 3.1 Dch t bo cht L phn dch lng ca t bo cht, khng mu, hi trong sut, n hi, khng tan trong nc. Thnh phn chnh ca dch t bo cht l nc, ngoi ra cn c cc i phn t protid, lipid v glucid. Cc i phn t ny lm thnh cc micel, cc micel mang cng in tch y nhau gy nn chuyn ng Brown ca t bo 2 3 1 4 cht. Do s hin din ca cc micel nn dch t bo cht trng thi keo, va c th trng thi lng (sol) va trng thi c (gel). Trong t bo sng thng xuyn c s thay i gia hai trng thi trn. Dch t bo cht l ni xy ra cc phn ng ca cc qu trnh trao i cht trong t bo 3.2 Khung xng t bo Cc bo quan tri ni t do trong dch t bo cht ca t bo nhn tht hoc chng c th gn vo h thng si protein phc tp bn trong, c gi l khung xng t bo. Ci sn protein ny to hnh dng ca t bo, tham gia vo cc c ng ca t bo v c bit quan trng trong lc t bo phn chia. Ba thnh phn quan trng nht ca khung xng t bo l si trung gian, vi ng v vi si. Ba thnh phn ny c cu to bi nhng bn n v protein c th tp hp thnh si n hay i v c th lm thay i hnh dng ca t bo hay gy ra cc c ng (hnh 1.16 v 1.17). a. Si trung gian: Cc vi si trung gian c tm thy nhiu t bo chu nhiu kch thch c hc nh t bo thn kinh nn c l chng lm thnh ci khung chng cho t bo v nhn ca chng. Bn n v cn bn cu to nn si trung gian gm hai phn t protein qun xon 7 nhau. Bn n v cn bn ny xp thnh tng 6 5 i (mt t phn), cc i ny gn ni tip Hnh 1.16 Khung xng ca t bo tng qut nhau t u n ui to thnh si ging nh 1. Mng nhn; 2. Hch nhn; 3. Li ni cht nhn; 5. Th rib; dy thng. Tm si i ny to thnh mt 4. Khung xng t bo; 7. Ty th 6. Li ni cht ht; ng rng (hnh 1.17c).



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b. Vi ng: Vi ng gi vai tr quan trng trong h thng mng ca khung xng t bo. Vi ng c cu trc hnh tr di, rng cu to bi cc phn t protein hnh cu tubulin. Mi tubulin gm hai protein to thnh mt chng xon c gm 13 bn n v (hnh 1.17a). Vi ng tng trng nh s gn thm vo ca nhng phn t tubulin vo mt u ca si v gi vai tr quan trng trong cu trc v trong s phn ct ca t bo. Trong lc t bo phn chia vi ng c thnh lp v ta ra t mi cc ca t bo to ra thoi vi ng cc nhim sc th trt trn v hai cc ca t bo hnh thnh nhn mi. Ging nh vi si, chng cng tham gia vo s chuyn vn bn trong t bo v gip to hnh dng v nng cho t bo cng nh cc bo quan ca n. Vi ng cn c vai tr chnh trong cu trc v c ng ca tim mao v roi. c Vi si (vi si actin): Vi si di, cc mnh, lm thnh si i, qun xon do cc protein actin trng hp to thnh (hnh 1.17a).Mng t bo Li ni cht ht Th rib

Si trung gian Vi ng Si actin

Hnh 1.17 Cc phn t lm thnh khung xng t bo a). Si actin; b) Vi ng; c). Si trung gian

Vi si actin gi vai tr cu trc, chng an cho nhau gi hnh dng t bo. Si actin khi kt hp vi myosin tham gia vo s c ng ca t bo. Si myosin di, mnh, rt ging si actin, nhng c mt u to. im c trng ca s kt hp actin-myosin l khi c cung cp nng lng ATP th phn u ca si myosin mc vo si actin v un ngc li. S c ng ny lm cho mng c ng ko theo s c ng ca cc si actin khc. iu ny gii thch c cc chuyn ng nh s co c, s vn chuyn ca cc ti chuyn ch bn trong t bo, vng gia ca t bo m tht li tch hai t bo con, c ng amip (hnh 1.18).

Hnh 1.18 Tng tc si actin v myosin



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4. Vch t bo v v t bo 4.1 Vch t bo thc vt Vch t bo l c im ca t bo thc vt phn bit vi t bo ng vt, vch bo v t bo, gi hnh dng, trnh s mt nc cng nh chng s xm nhp ca cc vi sinh vt. Vch pha ngoi ca mng c th dy t 0,1 n vi m. Thnh phn ha hc ca vch thay i t loi ny sang loi khc v t t bo ny sang t bo khc trong cng mt cy, nhng cu trc c bn khng thay i. Thnh phn cu to chnh l cc phn t celluloz c dng si c kt dnh vi nhau bng cht nn gm cc ng a khc v protein. Cc phn t celuloz cu trc thnh cc si celluloz xp song song nhau to ra cc tm, cc si trong cc tm khc nhau thng to ra cc gc t 60 1 90o. c im sp xp ny lm vch t bo rn chc. Cc si celluloz rng khong 2 20nm, gia cc si c nhng khong trng c th cho nc, kh v cc ion di chuyn t do qua mng li ny, tnh thm chn lc 3 ca t bo l do mng sinh cht quy nh (hnh 1.19). nhng cy cn non t bo c 4 vch mng gi l vch s cp, vch ny c tnh n hi v cho php t bo gia tng kch Hnh 1.19 Vch ca ba t bo thc vt lin k thc. Gia hai vch s cp ca cc t bo 1. T bo; 2. Tm ngn chung gia cc t bo; 3.Vch th cp; 4. Vch s cp lin k nhau l phin gia hay lp chung, l mt lp mng giu cht polysaccharid gi l pectin, thng hin din di dng l pectat calci. Khi cht pectin b ha nhy, cc t bo khng cn gn cht vo nhau na nh khi chn tri tr nn mm i. Khi t bo trng thnh v ngng tng trng, mt s t bo to thm lp cng hn gi l vch th cp nm gia vch s cp v mng t bo. Vch th cp thng dy c nhiu lp c cu to bng cc si celluloz xp theo nhiu hng khc nhau, nn vch t bo tr nn rn cht hn. Ngoi celluloz vch th cp cn c th tm thm nhiu cht khc nh lignin. Khi vch th cp c thnh lp hon ton, t bo c th cht i, khi ch cn lm nhim v nng hay dn truyn (hnh 1.19). Trn vch ca t bo thc vt c nhng l nh gip cc cht thng thng gia cc t bo vi nhau, cc l ny c gi l cu lin bo, v tr ny t bo cht ca hai t bo lin k lin tc nhau. 4.2 V ca t bo ng vt thc vt, nm v vi khun, vch t bo ring bit vi mng t bo, ngc li t bo ng vt, v khng c lp vi mng. Cc carbohydrate cu to nn v t bo thnh lp cc cu ni ha tr vi cc phn t lipid hay protein trn mng t bo. Kt qu to ra cc glycolipid hay glycoprotein, do v t bo cn c gi l glycocalyx. Lp ny nm bn ngoi. Theo cc nghin cu mi y, trong glycocalyx c nhng im nhn din trn b mt t bo, c im Hnh 1.20 Mng t bo ng vt ny gip cc t bo phn bit chng loi. (vi glycocalyx ca mng i lipid) Th d, trong mi trng cy cc t bo gan v thn ring r c trn u, sau mt thi gian cc t bo gan nhn ra cc t bo cng loi v t hp li vi nhau, tng t iu ny cng xy ra nhng t bo thn. Cc sinh vt k



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sinh cng nh cc carbohydrat trn glycocalyx nhn ra t bo ch xm nhp vo. C ch nhn dng mc phn t ny cng thng gp nh trng hp cc phn ng d ng vi cc cht l cng nh trong s dn truyn cc xung thn kinh t t bo ny sang t bo khc (hnh 1.20). 5. Tim mao v roi mt s t bo ng vt v t bo thc vt c mt hay nhiu si t ging nh tc c ng c b mt ngoi ca t bo. Nu ch c mt vi si v c chiu di tng i di hn so vi chiu di ca t bo th c gi l roi, nu c rt nhiu v ngn th c gi l tim mao. t bo nhn tht, cu trc c bn ca chng ging nhau, v hai t ny dng ln ln qua li. C hai c cu ny u gip cho t bo chuyn ng hoc lm chuyn ng cht lng quanh t bo. Thng gp hai c cu ny nhng sinh vt n bo v nhng sinh vt a bo c kch thc nh v giao t c ca hu ht thc vt v ng vt. Chng cng c nhng t bo lt mt trong ca cc ng, tuyn ng vt, cc tim mao ny gip y cc cht di chuyn trong lng ng. kh qun ngi, c th c n mt t tim mao trn 1cm2. Tim mao v roi l phn ko di ra ca mng t bo, vi mi mt nhm vi ng nm trong cht cn bn l t bo cht, trong c chn nhm vi tng i vi ng xp chu vi v hai vi ng n trung tm (hnh 1.21). Mi roi hay tim mao c mt th gc y. Tim mao v roi c ng khi vi ng ny trt qua mt vi ng khc. Cc vi ng ngoi bin c ni vi nhau bng cc tay protein, cc protein ny hot ng nh cc cu bt ngang gia cc i vi ng.1 2 3 4

2

6 7

5

8

a)

Hnh 1.21 Cu to chi tit ca tim mao v s hot ng ca chng Roi ca Trng roi; b) Ct ngang roi phn ngn; c) Ct ngang roi phn gc; d) Lng bi bao ph dy c trn c th Trng c (Paramoecium): 1. Cc i vi ng; 2. Mng bao; 3. Vi ng vng; 4. Vi ng trung tm; 5.Rnh phng x; 6. Roi; 7. Th gc; 8. Cc vi ng

Khi cc tay protein un cong li s y i vi ng ny qua mt v tr khc, sau cc tay ri ra v bt u bm vo v tr mi trn i vi ng, v qu trnh ny c tip tc gy ra s c ng ca tim mao v roi. S c ng ny cn nng lng do ATP cung cp.

IV. Cc i phn t quan trng trong t bo1. Carbohydrat, lipid, protein



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1.1 Carbohydrat Carbohydrat c cng thc chung l (CH2O)n; n v cn bn l nhng ng n. Nhng carbohydrat n gin hin din vi t l hai nguyn t H, mt nguyn t O (ging nh nc) ni vi mt C. Mt vi carbohydrat nh tinh bt v celluloz l nhng i phn t v rt phc tp, gm nhiu n v lin kt nhau. a. ng n (monosaccharide): nhng phn t carbohydrat cn bn l nhng ng n. Cc ng n cha t nht 3C, nhng chng c th cha 5, 6 hay nhiu hn. Cc ng 3, 5C c vai tr c bit trong t bo s c cp trong cc chng A B sau, cn ng 6C ngun cung cp nng lng cho t bo l nhng phn t ng n to ra cc ng phc tp khc. C rt nhiu loi ng 6C, trong glucoz v fructoz l hai loi ng quan trng nht. Glucoz l sn phm u tin ca qu trnh quang hp v tr C thnh ngun nguyn t C m Hnh 1.22 Cc loi ng n thc vt v ng vt. ng n A. ng 3 carbon; B. ng 5 carcon; C. ng 6 carbon c th c xp loi theo s nguyn t carbon. Trioz (glyceraldehyd) 3C, pentoz (riboz) 5C v hexoz (nh glucoz, fructoz v galactoz) 6C. Fructoz v galactoz l ng phn ca glucoz. Trong mt phn t ng n, mt C ni vi mt O bng ni i, trong khi nhng C khc trong chui ni vi mt nguyn t H v gc hydroxyl. Gc hydroxyl to cho phn t tnh phn cc v d dng tan trong nc. Hai ng n c th c cng cng thc ha hc nhng khc nhau v tr ca nhm C = O. Khi ni ny khng nm C tn cng chng to ra gc keton (- C = O). ng ketoz nh dihydroxyaceton, ribuloz v fructoz. Khi C = O nm cui chui n to ra gc aldehyd (CHO). ng aldoz nh glyceraldehyd, riboz, galactoz v glucoz (hnh 1.22). ng n c th dng dy thng, nhng trong nc chng Hnh 1.23 Cu trc chi tit ca glucoz lun lun dng vng theo mt



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trong hai cch. Dng alpha, v tr ca gc hydroxyl gn vi C th 1 pha di ca mt phng ca vng. Dng beta, nhm hydroxyl nm trong mt phng ca vng. S khc bit gia hai dng tuy t nhng rt c ngha trong sinh hc khi chng trng hp to ra cc i phn t. Th d trng hp ca -glucoz to ra tinh bt v ca -glucoz to ra celluloz (hnh 1.23). b. ng i (disaccharide): gm hai phn t ng n ni vi nhau bng ni glycosidic, C th nht ca mt phn t ng n phn ng vi mt gc hydroxyl ca mt phn t ng khc v mt mt phn t nc (hnh 1.24).

Hnh 1.24 S loi b phn t nc t 2 ng n to thnh 1 ng i a). T glucoz v fructoz to thnh Sucroz; b) T 2 phn t glucoz to thnh maltoz

Cc ng i thng thng nh sucroz, maltoz v lactoz. Sucroz (hnh 1.25) gm hai phn t glucoz v fructoz v l dng glucoz vn chuyn trong cy t ni quang tng hp l n nhng ni khc trong cy. Maltoz gm hai phn t glucoz c nhiu la m, la mch c dng lm ru bia. Lactoz l ng i gm glucoz v galactoz v l dng ng ca ng vt hu nh to sa cho con. Ngoi ra cn trng ng c vn chuyn trong haemolymph (mu) l trehaloz, mt ng i gm hai phn t glucoz. c. ng a (polysaccharide): gm nhiu ng n ni vi nhau thnh dng thng hay phn nhnh, chng c th c to thnh t mt loi ng, hai loi ng hay nhiu hn na. Chng thng khng c v ngt, l nhng hp cht khng tan, trng lng phn t cao, c gi dng d tr hay c chc nng cu trc.

Hnh 1.25 Cc ng i

ng a phong ph nht l celluloz c tm thy thc vt. G ca thc vt gm 50% l celluloz cn si bng vi hu nh 100% l celluloz. Celluloz l nhng ng a dy



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thng gm cc n v glucoz ni nhau (hnh 1.26a). Celluloz ch c thy phn khi c enzim cellulaz xc tc, enzim ny ch c mt s vi khun, nguyn sinh ng vt v nm, khng c ng vt. Mt s ng vt c th tiu ha c celluloz nh cc sinh vt cng sinh trong rut ca chng nh Kangaroo c vi khun v mi c nhng nguyn sinh ng vt sng trong ng tiu ha ca chng. Tinh bt l mt loi ng a d tr chnh ca thc vt bc cao c hp thnh do amyloz v amylopectin (hnh 1.26b v hnh 1.26c). Amyloz gm hng trm phn t glucoz ni nhau thnh chui di khng phn nhnh.

Hnh 1.26 Cc ng a phn t a) Celluloz; b) Amylopectin; c) Amyloz

Mi ni glycosidic c thnh lp gia C th nht ca phn t glucoz ny vi C th t ca phn t khc. Phn t amyloz c xu hng cun trn li trong nc do khng tan. Amylopectin l nhng ng a phn nhnh, dy ngn khong 20 - 30 phn t glucoz. Cc dy nhnh gip chng khng tan v khng t on. Tinh bt khoai ty gm 20% amyloz v 80% amylopectin. Inulin, cht d tr cc c ca cy h Cc (Asteraceae), gm nhng n v fructofuranoz c ni vi nhau bng nhng ni glycosidic. Glycogen l nhng ng a d tr chnh ca ng vt, chng c cu trc tng t amylopectin, nhng phn nhnh nhiu hn.Thc vt cn c cha nhng ng a c cu trc khc nh pectin (gm arabinoz, galactoz v acid galacturonic) v hemicelluloz. Chitin l thnh phn cu to ca b xng ngoi ca cn trng, gip xc v vch t bo nm. Chitin l mt dng bin i ca celluloz, trong mt gc c cha nit c thm vo mi n v glucoz (N-acetyl-D glucosamin) (hnh 1.27). 1.2 Lipid Lipid c nhiu chc nng sinh hc quan trng: l thnh phn cu trc mng, d tr, chng lm thnh ci o bao bc v bo v cho sinh vt khng thm nc, yu t lin lc ha hc c bn trong t bo v gia cc t bo. Lipid khng tan trong nc do c cu to bng nhng ni C - H khng phn cc, chng ngn cn cc phn t nc xm nhp vo v kt qu l nhng phn t lipid kt t li vi nhau to ra nhng git khng tan. Tuy nhin, chng d dng tan trong cc dung mi hu



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c nh chloroform. Lipid cng gm C, H, O nhng O rt t, ngoi ra, chng cn c cha nhng nguyn t khc c bit l P v N. Cc loi lipid khc nhau l: m, du, sp, phospholipid, glycolipid v steroid (hnh 1.28).

Hnh 1.27 Chitin

Hnh 1.28 Lipid: a) Photpholipid; b) Triacylglycerin; c) Terpen; d) Steroid

a. Lipid d tr (du v m): Tt c m u c sn chnh l glycerol, cha 3 nguyn t C, mi phn t ni vi mt chui acid bo to ra mt triglycerid. Acid bo l mt chui nhng hydrocarbon vi chiu di thay i v tn cng l nhm carboxyl (-COOH), cc acid bo c ni vi phn t glycerol nhm carboxyl; cc acid bo trong du v m n c cha t 4 - 24 nguyn t C. Ba loi acid bo chnh l acid stearic (18 C), acid palmitic (16 C) v acid oleic (18 C). Acid bo c s lng H ti a c gn vo C (nh acid stearic) c gi l bo ha v khng c ni i gia hai nguyn t C nh b, m heo v m cc ng vt khc. Acid bo vi cc ni i c gi l cha bo ha nh du olive, du bp, thng dng lng nhit thng. Du c hn mt ni i c gi l nhiu ln cha bo ha. Margarin cha bo ha cha 70% ca du nhiu ln cha bo ha c xu hng c thay th



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b trong ba n hng ngy ca nhng ngi n king v cc m bo ha gy cc bnh v mch mu. Cng mt n v trng lng, du v m cha nhiu nng lng hn carbohydrat do cha nhiu cc ni C - H, trung bnh 1g m cha nng lng gp 2 - 3 ln nhiu hn carbohydrat hay protein. b. Lipid bo v - sp: Sp tng t nh m ch khc l acid bo c ni vi mt chui alcol di hn glycerol, sp khng ha tan trong nc, khng c ni i trong chui carbon v tr i vi cc phn ng ha hc, chng lm thnh lp bo v b mt ngoi ca nhiu ng vt bao gm c b xng ngoi ca cn trng, lng v ca chim v lng mao ca th v c lp biu b ca l v tri ca thc vt. c. Lipid mng - phospholipid v glycolipid: Phospholipid tng t nh du v m ch khc l chng c hai phn t acid bo gn vo mi phn t glycerol v mt nhm phosphat gn vo C th ba (hnh 1.29). V gc phosphat mang in tch m nn u phosphat ca phospholipid a nc v tan trong nc, ui acid bo k nc, khng tan trong nc. S khc bit v tnh cht i vi nc ca hai u ca phn t (nn c tn l lng i) gi cho phospholipid d dng to thnh mng i trong cu trc t bo (hnh 1.30).ui k nc u a nc

Hnh 1.29 Phospholipid

Vng a nc Vng k nc Vng a nc

Hnh 1.30 Cu trc phospholipid 1. ui k nc; 2. u a nc; 3. Vng a nc; 4. Vng k nc

Khi phospholipid c a vo nc, u k nc b y ra khi nc v t tp li vi nhau to ra cc micel hay mng hai lp lipid. Glycolipid: l lipid c ng cng l thnh phn quan trng trong mng t bo, ging phospholipid c hai acid bo gn vo phn t glycerol, nhng c mt dy carbon ngn t 115 ng n ni vo C th ba. Glycolipid cng lng i v to thnh micel khi gp nc tng t phospholipid. d. Steroid: cu trc phn t ca steroid hon ton khc cc lipid khc. Steroid c cu trc gm 4 vng carbon, dn xut t cholesterol c th thm vo mt s ui hydrocarbon khc nhau. Steroid l nhng phn t quan trng trong ng vt c xng sng, chng c tm thy tim, mch mu v gan. Mt s hormon v vitamin cng l steroid. Mt trong steroid nhiu nht l cholesterol, l thnh phn cu to mng ca tt c t bo ng vt v l



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im khi u tng hp ra cc hormon. Cholesterol, khng tan trong nc, c th kt ta bi mt trong ti mt, to ra si mt. Chng tch t trong cc ng mch lm tng huyt p v nguy c suy tim v nhi mu c tim ngi v nhng ng vt khc. Mc cholesterol trong mu khng nht thit l do ch n ung ca con ngi m ty thuc nhiu hn vo t l tng hp cholesterol ca c th (hnh 1.31).

Cholesterol

Testosterol

1.3 Protein C cu trc phn t v chc nng rt thay i: l cc enzim, protein cu trc, c ng, tn tr, dinh dng, vn chuyn, khng th v toxin bo v v tn cng. Ngoi ra cn l hormon iu ha cc chc nng ca c th. Protein cha C, H, O, N v thng c S. n v cu to protein l acid amin. Ch c 20 loi acid amin khc nhau c tm thy trong protein. Tuy nhin, s t hp ca acid amin s to ra rt nhiu loi protein (hnh 1.32). a. Acid amin: Mi acid amin c cha mt gc amin (- NH2, tr prolin c cha mt gc imino - NH -), mt gc carboxyl (COOH), mt H v mt chui bn l gc R gn vo C trung tm. Cc acid amin ch khc nhau gc R, c th ch l mt nguyn t H nh glycin, hay phc tp nh cu trc c hai vng nh tryptophan. C ba acid amin c chc nng c bit l methionin - l acid amin c bit c tng hp u tin trong qu trnh tng hp protein, prolin lm cho chui acid amin xon li v cystein ni cc chui acid amin li vi nhau. Mt s gc R phn cc (a nc), mt s khc th khng. S khng phn cc ca chui bn lm cho protein khng tan trong nc. Cc acid amin c vit tt bng ch mt ch ci (A). b. Polypeptid: Mt chui acid amin c gi l polypeptid. Acid amin trong chui polypeptid c ni vi nhau bng lin kt peptid, c to ra khi gc - COOH ca mt acid amin ny gn vi gc - NH2 ca acid amin khc v gii phng mt phn t nc (hnh 1.33). Khi cc acid amin lin kt nhau to ra polypeptid lun lun c mt gc amin t do mt u N v mt gc carboxyl C tn cng ca u kia, mt protein c th gm mt hay nhiu si polypeptid vi hng trm acid amin theo mt trnh t c bit. Cc si polypeptid c th lin kt cho vi cu ni cng ha tr l cc cu ni disulfid, c to ra gia hai nguyn t S ca hai acid amin cystein. Cu ni disulfide c th ni cc cystein trong cng mt chui polypeptid hay gia cc chui polypeptid khc nhau, kt qu l to ra cu trc khng gian ba chiu ca protein. c. Cu trc ca protein: Protein c chia lm hai loi chnh: n gin v phc hp. Protein n gin ch cha acid amin. Protein phc hp gm acid amin v cc thnh phn hu c hay v c khc, th d: nucleo-, lipo-, phospho- v glycoprotein. Nhng thnh phn khng phi l acid amin ca protein phc hp c gi l gc prosthetic.

Hnh 1.31 Cc Steroid: Cholesterol v Testosterol



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Hnh 1.32 Cc loi axit amin

Cu trc cp mt (s cp) ca mt protein l do trnh t thng ca cc acid amin trong chui polypeptid. Mi loi protein c cu trc cp mt khc nhau (hnh 1.34a). Cu trc cp hai ca protein l do cc cu ni hydro gia cc acid amin nm k nhau trong cu trc cp mt. Th d mt cu trc cp hai xon phi (ging nh mt cu thang xon) (hnh 1.34b).



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Hnh 1.33 S thnh lp ni peptid gia hai acid amin

Cu trc cp ba l do cc polypeptid c cu trc cp hai xp chng ln nhau, to ra mt khi hnh cu (hnh 1.34c). S cun li thng do s tng tc gia cc acid amin tng i xa nhau trong. Hnh dng cui cng cng do nh hng ca mi trng, c bit l pH, do nhng vng c in tch trn phn t cng nh hng ln hnh dng phn t. Hnh dng ca phn t quan trng c bit nhng protein nh hormon, l nhng thng tin ha hc ch nhn protein ng hnh dng tng thch vi n nh kiu cha kha v kha. Mt s protein c kch thc ln nh hemoglobin, cha hn mt chui polypeptid, c cu trc khc hn, cu trc cp bn (hnh 1.34d v 1.35). Hu ht nhng protein c kch thc ln c bit l enzim c cha hai si polypeptid hay hn na. Hnh dng khng gian ba chiu ca protein c gi l dng hay cu hnh ca protein. Ty theo dng protein c chia ra lm hai loi chnh: protein hnh si v protein hnh cu. Trong protein hnh si, cc si polypeptid xp song song nhau theo mt trc n to ra cc si hay bn (collagen, keratin, elastin). Protein hnh si (hnh 1.36) khng tan trong nc v thng rn chc v l thnh phn cu to chnh ca tc, mng, sng v vut. protein hnh cu, cc si polypeptid cun cht thnh hnh trn hay hnh cu. Protein hnh cu tan trong nc v gm hu ht cc protein chc nng nh enzim v cc hormon.

Hnh 1.34 Cu trc ca protein a). Cu trc bc 1; b) Cu trc bc 2; c) cu trc bc 3; d) Cu trc bc 4


Tai lieu chia se tai: wWw.SinhHoc.edu.vnNhm heme Chui bta

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Chui anphaHnh 1.35 Cu trc khng gian ca hemoglobin

Hnh 1.36 Protein hnh si

2. Enzim Cc phn ng ha hc xy ra trong t bo sng c tng tc nh nhng cht xc tc sinh hc, c gi l enzim, thng l cc protein. Mt t bo ng vt, c th cha n 4.000 loi enzim khc nhau, mi loi xc tc cho mt phn ng ha hc khc nhau. Mt s enzim chung cho nhiu loi t bo, trong khi mt s khc ch chuyn bit cho mt loi t bo thc hin mt chc nng c bit. Trong mt phn ng c enzim, cht phn ng c gi l c cht. Hu ht enzim c tnh chuyn bit v ch phn ng mt cch chn lc trn mt loi c cht no m thi. L cht xc tc, enzim gim nng lng kch ng cn thit cho mt phn ng xy ra trong iu kin nhit v sinh l bnh thng (th d 370C hu ht ng vt c v). Enzim c th mang hai cht li vi nhau nh to ra s phi hp tm thi gia cc c cht hay tp trung vo mt cu ni ho hc c bit trn c cht. Tt c enzim c dng i dng li. Enzim c kh nng xc tc siu tc. Th d, phn ng gia CO2 + H2O to ra H2CO3 phn ng xy ra rt chm, c th ch to ra 200 phn t acid carbonic/1 gi khi khng c enzim. Trong t bo sng, phn ng c xc tc vi enzim carbonic anhydraz c chng c 600.000 phn t acid carbonic/1 giy ngha l phn ng nhanh gp 10 triu ln. Trong cu trc khng gian ba chiu, si polypeptid ca enzim cun li to ra mt hay nhiu rnh trn b mt, l nhng vng c bit m c cht c th gn vo. Vng ny c gi l im hot ng, gi tt l hot im (hnh 1.38). Hot im ca mi enzim c hnh dng c bit v ch c mt loi phn t c cht c th gn vo. Hot im khng nhng l ni c cht gn vo m hng c cht theo mt hng nht nh. Hot im c th phn cc hay khng, a nc hay k nc nn n gn mt cch chnh xc vo phn no ca c cht. Th d nu phn phn t c cht c in tch dng th hot im ca enzim s c in tch m. Hot im ca enzim ch gm vi acid amin ca ton th enzim, nhng acid amin ny k cn nhau trong mt chui polypeptid hay nhng phn khc nhau ca cc chui polypeptid nhng k cn nhau do s cun li to ra cu trc khng gian ba chiu cp ba v cp bn ca enzim. Gc R ca acid amin c a ra ngoi to ra hot im v cch sp xp ca chng quyt nh s gn c cht vi enzim.



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a. M hnh hot ng ca enzim: + M hnh v cha kha: Mmt c cht gn vo hot im nh mt cha kha gn kht vo , c cht v enzim gn vo nhau to ra mt phc hp enzim-c cht. C cht b bin i mt cch chuyn bit v kt qu l sn phm c phng thch (hnh 1.37).1 2 4

3

5

Hnh 1.37 M hnh c ch xc tc ca enzim 1. Hot im; 2. Enzym; 3. C cht; 4. Phc hp enzym-c cht; 5. Sn phm

+ M hnh cm ng: Cc nghin cu cu trc ca enzim cho rng hot im linh ng hn l ca kha. Trong mt s trng hp, trong lc c cht gn vo, cu hnh thay i do hnh dng hot im ca enzim b cm ng lm cho chng khp vi nhau hn. S cm ng ny lm thay i lc gia cc ni c bit ca phn t phn ng do phn ng c xc tc c d dng xy ra (hnh 1.38).1 2 1 2

Hnh 1.38 M hnh v cha kha v M hnh cm ng 1. Enzym; 2. Enzym gn vo c cht

S tc ng tng qut ca enzym phn gii saccharoz thnh glucoz v fructoz c trnh by hnh 1.39. b. Cc yu t nh hng ln hot ng ca enzim: + pH c th lm thay i cu hnh ca enzim, c bit l s tng tc gia nhng acid amin c in tch m (acidic) v in tch dng (basic). Khi pH thay i, hnh dng ca hot im c th thay i, do c cht khng th gn vo c. Hu ht enzim hot ng tt nht trong khong pH 6 - 8. Tuy nhin, pepsin gip tiu ha protein trong bao t hot ng trong khong pH rt thp (khong bng 2). Pepsin c mt trnh t acid amin duy tr cu ni hydro v ion ha ngay c khi c s hin din ca acid mnh. pH cng nh hng trn phn ng trong ion H+ l mt thnh phn ca s thay i ha hc c xc tc.


Tai lieu chia se tai: wWw.SinhHoc.edu.vnC cht l ng saccharoz gm glucoz v fructoz lin kt vi nhau C cht v enzym gn vi nhau to thnh phc hp c cht - enzym

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Sn phm c gii phng, enzym c t do ri khi c cht

S gn c cht vo v tr hot ng ca enzym v mi lin kt glucoz -fructoz b b gy

Hnh 1.39 S tc ng tng qut ca enzym phn gii saccharoz thnh glucoz v fructoz

+ Nhit thay i d lm t cc cu ni hydro, cc cu ni ny v s tng tc gia cc cc k nc gip gi cu trc cp ba, cp bn ca protein k c enzim. Sinh vt thng c nhng enzim hot ng ti u nhit m chng sng. c v, nhit ti u t 35 400C. Di nhit ny, cc ni gi hnh dng ca protein khng linh ng thay i hnh dng cn thit tham gia phn ng. Do , enzim hot ng khng hu hiu nhit di 350C. Trn 400C, cc cu ni hydro v cc cu ni yu khc khng th gi protein hnh dng chnh xc ca n. Mt enzim b bin tnh mt phn bi nhit c cu trc b quo li mt cht v chui polypeptid thay i cu hnh (conformation) c th tr li hnh dng c nu c lm ngui, nhng nu bin tnh hon ton nh albumin ca trng luc chn th khng th tr li dng ban u c na. c. Cofactor v coenzim: Nhiu enzim cn phi c thm cc thnh phn ha hc khc thc hin chc nng, phn thm c gi l cofactor. Cofactor c th la mt phn t hu c hay cc ion kim loi (st, mangan, km...). Khi cofactor l mt phn t hu c khng phi l protein, nh mt vitamin, th c gi l coenzim. Tng t enzim, coenzim cng c s dng li sau khi xc tc phn ng. D cn vi mt lng rt nh nhng nu thiu coenzim th rt tai hi i vi i sng sinh vt, cho nn trong khu phn cn phi c vitamin. Coenzim v cofactor c tm thy cc enzim trong cc chui dn truyn in t ca cc qu trnh quang hp v h hp ca t bo.


Tai lieu chia se tai: wWw.SinhHoc.edu.vnChng 2.

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Mng t boI. Thnh phn ha hc ca mngThnh phn cu to chnh l lipid v protein, carbohydrat c mt vi mt t l rt t. 1. Lipid 1.1 Phospholipid Mng t bo c cu to bi phn ln l phospholipid. Phosphatidylcholin, l mt loi phospholipid hu nh ch tm thy na lp ngoi ca mng, gm c mt u phn cc (cholin mang in tch dng, phosphat mang in tch m v mt glycerol khng phn cc) c ni vi hai si acid bo k nc, np gp trong ui bn phi to ra do ni i. Nh vy ui cha bo ha, phospholipid nh vy s t gn cht vi nhau v nh th mng s linh ng hn (hnh 2.1).

u a nc

u k nc

u a nc

Hnh 2.1 Cu to lp phospholipid kp trn mng t bo

Mt phospholipid l mt phc hp n gin ca triacylglycerin, bn ngoi c 2 phn t axit bo gn vo mch thng ca phn t glyceron. Mt alcohol phosphoryl ho chim gi vj tr th 3 ca mch thng phn t glycerin. Alcohol phosphoryl ho thng dui v mt bn ca phn t v 2 phn t axit bo vo mt mt khc. Do cc phospholipid thng c s l mt u a nc v mt u k nc (hnh 2.2). 1.2 Cholesterol Cholesterol c tc dng ngn cch hai phn t phospholipid, nu khng cc ui phospholipid s dnh vo nhau gy tnh trng bt ng, hu qu l s lm cho mng t linh ng v tr nn cng rn (hnh 2.3). Hm lng cholesterol thay i rt ln theo loi t bo, mng ca nhiu loi t bo cha s phn t cholesterol gn nh bng s phn t phospholipid, trong khi mt s loi mng khc gn nh hon ton khng c cholesterol. 2. Protein trong mng t bo Trung bnh protein chim 50% trng lng cc phn t cu to mng. Do phn t lipid nh hn phn t protein nn nu protein chim 50% trng lng th s phn t lipid nhiu gp 50 ln s phn t protein. Tuy nhin, protein mng myelin ca t bo thn kinh ch chim



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khong 25% hay c th ln n 75% mng trong ca ty th v lc lp. Trong mng t bo c cha hai loi protein, c phn bit ty theo cch sp xp ca chng trong mng. a. Protein ngoi vi (xuyn mng): Protein gn vo u phn cc ca phn t phospholipid, do c th thay i v tr v c th b ly mt i do mt tc nhn no (nh cc cht c cha nhiu mui). Chiu dy ca mng ty thuc s hin din vo cc protein ny, mng sinh cht dy nht 9nm, mng ca mng ni cht mng nht 6nm. Ngoi ra, s c mt ca cc protein ngoi vi ny lm cho cu trc mng c tnh bt xng (hnh 2.4). b. Protein hi nhp: Protein hi nhp c th c vi kiu sp xp: protein c th ch tng tc vi vng k nc ca cc phospholipid, mt s protein hi nhp c th xuyn qua mng c gi l protein xuyn mng. Trong cch sp xp, protein vi cc acid amin a nc c a ra protein xuyn mng. Trong cch sp xp, protein vi cc acid amin a nc c a ra ngoi, ni c th tip xc vi nc (u phn cc hay acid amin c gc R c in tch dng), ngc li nhng acid amin k nc (khng phn cc) c chn trong mng i lipid (hnh 2.4). V tr ca nhng acid amin a nc v k nc ca protein s gip cho protein hi nhp mt phn vo mng hay xuyn mng. Protein hi nhp ch c tch ra khi lm v mng v sau x l bng cc cht ty. 3. Carbohydrat Cc carbohydrat thng gn vo cc protein ngoi vi to ra glycoprotein hay gn vo cc phn t phospholipid mng to ra glycolipid v thng ch chim 2 - 10% thnh phn cu to. Carbohydrat khng c trn mng pha t bo cht, cc phn t carbohydrat ny to ra glycocalyx, lp v bao ngoi t bo (cell coat). Carbohydrat hin din bn trong ca cc bo quan trong t bo ( trong lumen). S c mt ca cc carbohydrat trn mng sinh cht cng to ra tnh bt xng trong cu trc ca mng.axit bo

axit bophotphoryl ho alcohol

Vng l (hydrophilic)

Vng khng c l (hydrophobic)

Hnh 2.2 Cu trc phospholipid a) Mt photpholipid trong phc cht b) Cu trc vng c l (hydrophilic) v vng khng c l (hydrophobic)

Hnh 2.3 Cu trc phospholipid v cholesterol trn mng t bo

II. M hnh cu trc dng khm ca mngKhong 1930 J. F. Danielli v H. Davson, a ra m hnh cu trc mng gm mng vi hai lp phospholipid vi u a nc (phn cc) a ra hai b mt ca mng v cc ui k nc, (khng phn cc) chn bn trong trnh nc. Cu trc da trn s tng tc gia tnh k nc v a nc lm cho mng rt bn vng

Hnh 2.4 Protein xuyn mng v hi nhp trong mng t bo



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v n hi. Cu trc ny tng t nh khi trn cc phn t phospholipid vi nc, cc phn t phospholipid s sp xp li to ra cc khi rng ging nh th lipo gm hai lp phospholipid. Mc d m hnh trn gii thch c tnh bn vng, linh ng ca mng v c bit l cho cc cht lipid i qua li mng mt cch d dng nhng m hnh trn khng gii thch c tnh thm chn lc ca mng i vi mt s ion v mt s hp cht hu c. Sau hai ng ngh thm l c hai mt ca mng c bao bc bi protein, mang in tch, cc phn t protein vin quanh cc l, gip cho nhng phn t nh v mt s ion xuyn qua c. Nhiu bng chng cho thy m hnh ny hin nay khng cn ng na. Vo nm 1972 S. J. Singer v G. L. Nicolson a ra m hnh dng khm, mt gi thuyt hin nay c mi ni chp nhn. M hnh ny l s hp nht ca m hnh mng ca Danielli - Davson. Tuy nhin, trong m hnh dng khm s sp xp ca protein rt khc bit. Thay v protein ph hai bn mng, c nhng phn t protein chuyn bit gn vo mng, m nhn cc chc nng c bit. Hai lp lipid trong phn ln l phospholipid to ra phn chnh lin tc ca mng, mng ca sinh vt bc cao c thm cholesterol. Protein vi nhiu kiu sp xp khc nhau: mt s c gi l protein ngoi vi nm trn b mt ca mng, ni vi cc lipid bng cu ni cng ha tr, mt s khc c gi l protein hi nhp, gn mt phn hay ton phn vo mng lipid, mt s khc xuyn mng (hnh 2.5).Dch tit ngoi bo Protein vn chuyn qua mng

Protein hnh cu

Hnh 2.5 M hnh cu trc dng khm ca mng t bo theo Singer v Nicolson

Tnh linh ng ca mng l do cc phn t lipid c th di chuyn qua li, tnh khm ch s sp xp ca cc phn t protein trn mng hay xuyn mng. Trong hnh 2.6 m t th nghim trn ln t bo ca ngi v chut, dng cc khng th nh du vi flourescein cho protein mng ca chut v rhodamin cho protein mng ca ngi. Khi dung hp t bo, hai loi protein hai pha khc nhau, nhng sau khi 40 pht 37 oC hai mng thng nht li thnh mt mng lin tc v hai loi protein th xp xen k nhau. Cc protein c nhn ra vi knh hin vi hunh quang. Cc phn t lipid mng t bo vi khun c th c ko di ra n 2,5m trong vng t 1 n 2 giy. Mt s protein c th di chuyn qua li t pha ny sang pha khc ca mng, mt s bt ng do gn cht to thnh si hay to thnh ng. Cc phn t lipid v protein cng c th xoay trn hay lt ngc, dp xung tng i d dng.

III. Knh trn mng t bo



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Nh bit, mng t bo do chnh phospholipid ca t bo to ra. Mng tuy linh ng nhng l mng chn hiu qu gia bn trong v bn ngoi t bo. Thnh phn lipid trong mng rt cao, iu gii thch c ti sao nhng phn t ha tan trong lipid c th khuch tn vo ra d dng, nhng i vi mt s cht khng ha tan trong lipid phi ty thuc vo cc protein trn mng i lipid. Nh vo cc protein trn mng mt s cht c th i qua mng mt cch d dng ngc li vi gradient nng ca n. Mng c tnh chn lc rt cao. Tnh chn lc ny trn tng phn ca t bo l do cc tc nhn ti (hay cht vn chuyn) l nhng protein hot ng nh enzim. By gi ngi ta bit c nhng yu t vn chuyn, kim sot s qua li

K+

K+

K+

K+

K+Hnh 2.6 Th nghim chng minh tnh dng khm ca lipid v protein

Hnh 2.7 Knh khuch tn

ca cc phn t qua mng l nhng knh v nhng bm chuyn bit. Mi loi kinh hay bm ty thuc vo protein mng cho mt s ha cht c bit xuyn qua nn c gi chung l permeaz. 1. Cc kiu knh qua mng t bo 1.1. Knh khuch tn L kiu knh n gin nht trong s vn chuyn th ng nh tnh thm c bit cao ca mng t bo: chng cho mt s cht c bit i qua t ni c nng cao n ni c nng thp hn. Th d knh protein ny cho ion K +, c tch ly trong hu ht t bo v c in tch nn khng th ha tan trong mng phospholipid, nhng knh c bit dnh cho ion K+ cho php chng i qua mt cch t t vi nng kim sot c. Nu khng c s i ra ny nng ion K+ bn trong t bo s tr nn rt cao lm nh hng n cc chc nng



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ca t bo. S chuyn bit ca knh ion K+ l kt qu ca hnh dng bn trong v in tch, nhng cn nhiu chi tit v n cha c bit r (hnh 2.7). 1.2 Knh ion phi hp L kiu knh phc tp hn cho hai cht qua cng chiu. Th d, ion Na + bn ngoi t bo cao hn 11 ln nn Na+ phi c glucoz i km mi xuyn qua knh thch hp trn mng vo c bn trong t bo. C hai phi gn vo pha ngoi knh trc khi knh c m ra. Khi ion Na+ gn vo knh, c th gy ra mt cm ng g lm cho glucoz cng gn c vo knh. S gn glucoz c th gy ra mt hu qu khc, c th lm ng knh pha ngoi mng v m knh ra pha trong mng. S thay i ny, c th lm cho knh mt i lc i vi glucoz v gii phng glucoz cng nh ion Na+ vo bn trong t bo. Mt ion Na+ v glucoz lm knh m li pha ngoi mng (hnh 2.8).Na+ G

Na G

1.3 Knh c cng Mt kiu kim sot s di chuyn vt cht qua mng l nh mt cng ngang qua knh. Khi mt phn t tn hiu, mt hormon hay mt cht truyn ti mang thng tin t mt t bo thn kinh ny sang mt t bo thn kinh khc, gn vo mt th th (receptor) l mt protein xuyn mng, lc c s thay i cu trc. S thay i ny lm cho cng m ra v tn hiu th hai, thng l mt ion nh ion Na+ hay Ca++, c th i qua mang thng tin vo trong t bo. Kiu knh ng m ny vn chuyn nhiu thng tin ha hc c thc vt v ng vt, cc xung thn kinh nh ng vt cm nhn th gii bn ngoi, cc c ng v c l ngay c suy ngh (hnh 2.9). 1.4 Knh ti c ng Mt kiu permeaz khc hot ng nh mt cht ti c ng, ti tng phn t mt. Cha c mt th d chc chn no v kiu permeaz ny. Nhng valinomycin hot ng y nh mt cht ti c ng. Valinomycin l mt a phn dng vng vi u k nc ngoi v u phn cc trong, vi 6 nguyn t oxy xp thnh hng c th gi mt ion K+.Na+ Phn t tn hiu Na+ ng Na+ M Na+

Hnh 2.8 Knh ion phi hp

Na+

G

Na+

Na+

Tai lieu chia seHnh 2.9 Knh c cng tai: wWw.SinhHoc.edu.vn


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Phc hp hot ng nh mt qu lc qua li mang ion K+ c hai hng. S vn chuyn ion K+ da trn khuynh ha in: Valinomycin thng ly ion K+ trong t bo v phng thch ra ngoi mt cc n gin, v ion ny trong t bo nhiu hn ngoi. Valinomycin khng phi l mt protein, v mt n v trong chui peptid ca n khng phi l acid amin. y l mt cht khng sinh do mt s vi khun tit ra gy c cho nhng vi sinh vt xung quanh bng cch lm thay i tnh thm chn lc ca mng t bo ca cc vi khun ny. C mt vi bng chng chng t c cht ti c ng trn mt mng bnh thng, nhng hin nay vn vn cn nhiu nghi vn. thay i tnh thm chn lc ca mng t bo ca cc vi khun ny. C mt vi bng chng chng t c cht ti c ng trn mt mng bnh thng, nhng hin nay vn vn cn nhiu nghi vn (hnh 2.10).K+ K+ K+

K+

K+Hnh 2.10 Knh ti c ng

2. S ng vn chuyn v i vn chuyn 2.1 S ng vn chuyn L hin tng hai cht cng c ti qua knh i v mt hng. y l kiu vn chuyn quan trng xuyn qua mng ca glucoz, ngun nng lng quan trng cho hu ht t bo. Ion Na+ bn ngoi c khuynh nng cao gp nhiu ln so vi bn trong, nn c xu hng di chuyn vo bn trong t bo. N phi c ng vn chuyn vi glucoz i qua mt knh thch hp. Knh ny khng vn chuyn ring r, hai cht phi c gn vo pha bn ngoi ca knh trc khi knh c m ra. V vy nng lng t do ca ion Na + do khuynh nng cao c th c li dng ti glucoz mt nng nh hn. V mt nhit ng hc, hai phn ng khuch tn c lin kt vi nhau. Ion Na+ xung dc gii phng nng lng t do nhiu hn, nng lng ny c s dng vn chuyn glucoz ln dc, kt qu l qu trnh ng khuch tn din ra. 2.2 S i vn chuyn L hin tng phc tp hn, xy ra nhng knh trao i ion, vn chuyn hai ion mang in tch ging nhau: trong khi mt ion di chuyn vo bn trong t bo, mt ion khc i ra, cho nn duy tr c s cn bng in tch. Nhiu protein hi nhp trn mng c th trao i Cl- vi HCO3- (CO2 ha tan), y l vai tr ca hng cu mang CO2 thi ra t t bo n phi.

IV. BmMt kiu permeaz khc c gi l bm, s dng nng lng ca t bo a cc cht i ngc gradient nng . 1. Bm Na - K



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Trong kiu vn chuyn ny, bm s dng nng lng t trong t bo v gip vn chuyn cc cht ngc chiu gradient ca n. Trong trng hp ny, ba ion Na+ c i vi hai ion K+, c hai loi ion ny u c nng cao ni chng s c chuyn n. Trong m hnh: Hai ion K+ c gii phng trong chu k trc tip theo l s gn vo ca ba ion Na+ v ngun nng lng ATP t trong t bo. Hu qu cu trc protein knh thay i, m pha ngoi, gim i lc i vi ion Na+ v gii phng ion Na+; ng thi gia tng i lc i vi K+. S gn ca ion K+ lm knh m ra pha trong, gia tng i lc i vi ion Na+ v gim i lc i vi ion K+ v chu trnh bt u tr li. Kt qu l a in tch dng ra pha ngoi mng v bn trong mng tr nn m vi bn ngoi. in th v thm thu sinh ra bi bm Na - K sau cng c th phi hp vn chuyn glucoz. Gii thch nh sau: Knh protein c bit nh l mt bm Na (vn chuyn ion Na+) v bm K (vn chuyn ion K+) qua mng t bo. Mi mt ln bm c 3 ion Na + chuyn ra kh t bo th c 2 ion K+ chuyn vo t bo. Nng lng cung cp cho qu trnh bm l ATP. Qu trnh ny gm 6 bc: 1) Protein mng gn ion Na+ trong t bo; 2) ATP phosphoryl ho protein vi ion Na+ ; 3) Phosphoryl ho hon thnh v gii phng ion Na +; 4) Ion K+ ngoi mng t bo gn vo v tr; 5) S gn do qu trnh phn phosphoryl protein; 6) Phn phosphoryl ho kt thc v gii phng ion K+ vo trong mng t bo (hnh 2.11).a a a

b 1

b

2

b

3

4

5

6

Hnh 2.11 Bm Na - K (a. ngoi mng t bo; b. trong mng t bo)

2. Khuynh (gradient) ha in qua mng Gradient nng gii thch c s di chuyn kt hp ca ion Na+ v glucoz qua cng mt knh. C mt khuynh quan trng th hai h tr khuch tn cc ion ngc in tch hp dn nhau bng lc tnh in; trong khi nhng ion c cng du y nhau. Do vy, nu trong t bo c nhiu ion mang in tch m hn mang in tch nhng ion dng s b hp dn bi mi trng lng bao chung quanh n (hu ht t bo c mt tng in tch m chng 70 milivolt so vi cht lng bao quanh chng). S khc bit v in tch xuyn qua mng sinh ra mt gradient tnh in v khi knh thch hp c m ra, ion dng c xu hng chui vo trong t bo, trong khi nhng ion m c xu hng i ra. Th d ion Na +, c nng rt cao bn ngoi t bo, p sut thm thu v lc tnh in kt hp li sinh ra mt gradient ha in



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cao. y l nng lng t do ca s kt hp rt c hiu qu ca ion Na + vn chuyn glucoz vo trong t bo. C ch do gradient ha in cng hin din trong bm Na - K.



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S trao i vt cht qua mng t bo

I. Khi nim v s khuch tn v thm thu1. S khuch tn C th gii thch s khuych tn bng m hnh c hc trong th nghim sau: C mt ci hp c cha cc vin bi c gom vo mt gc, khi ta lc ci hp, cc vin bi s b phn tn v khp ni ca y hp. y cc vin bi l nhng phn t, ng tc lc l thm vo ng hay nhit nng. S lc lm phn tn cc hn bi tng t s di chuyn ca cc ht vt cht no i t vng c nng cao n vng c nng thp hn ca vt cht , kt qu l nhng ht vt cht c xu hng phn phi cch u nhau trong mt khong khng gian nht nh. Khi mt gn nh ng u, h thng c cn bng nhng cc ht vn tip tc chuyn ng, nhng c s thay i nh trong h thng (hnh 3.1).

A

B Hnh 3.1 M hnh c hc ca s khuch tn A cc vin bi trong gc; B. Cc vin bi phn tn u

Trong mi trng lng c th dng th nghim nh hnh 3.2. Gi s ta cho mt vin ng vo trong mt cc nc, lc u cc phn t ng ri khi vin ng, bt u khuych tn vo nc. Kt qu qu trnh ny l cc phn t ng phn tn u trong cc nc (hnh 3.2). S chuyn ng ca cc ht vi kch thc phn t t ni ny n ni khc theo cch trn c gi l s khuch tn. Tc khuych tn nhanh nht l cht kh, ri n cht lng v cui cng l cht rn.Vin ng Phn t ng khuych tn

Hnh 3.2 S khuych tn cc phn t ng trong nc a) B vin ng vo nc; b) Cc phn t ng khuych tn; c) Cc phn t ng bt u khuych tn; d) Cc phn t ng khuych tn u



34

Trong mt c th sng, cc phn t thng trong dung dch lng, m v khong cch ca phn t c o bng nhng phn s ca milimet nn s khuch tn l mt qu trnh rt quan trng; mt acid amin hay mt nucleotid trong mi trng lng s khuch tn chng bng ng knh ca mt t bo (10 - 50m) t hn 0,5 giy. S khuch tn nh trn l theo gradient nng . Trong c th sinh vt, s khuch tn khng n thun l do nng m cn ty thuc vo cc iu kin t khi n nh ni m cc qu trnh sng din ra. Nh vy cn c s khuch tn theo nng lng t do ca cc phn t tham gia. Nng lng t do l nng lng trong mt h thng c th dng thc hin mt hot ng no di mt iu kin nhit v p sut nht nh. Nng lng t do c cha trong cc cu ni cng ha tr ca ng nh glucoz, hay mt in t c hot ha bi nng lng nh sng mt tri ln mt qy o cao hn, hay trong vnh ai bao quanh nhn ca nguyn t trong phn ng ht nhn. S khuch tn xy ra mt cch t pht v nhng phn t sp xp c trt t v c nng cao c nng lng t do cao hn nhng phn t phn tn. Gi s c th quan st s khuch tn mc phn t th khi cho cc vin ng vo c ph: lc u cc phn t ng s khuch tn trong c ph, sau khi cc cht c trn u hn, phn ng ngc li s bt u tng cho n khi cn bng. R rng s khuch tn l mt phn ng ha hc vi nng lng t do ring ca n v n ty thuc vo tnh cht ca vt cht khuch tn. Nng lng t do l c s c th ng dng rng ri hn gradient nng hiu s khuch tn. Gradient nng mt hng v gradient nhit theo chiu ngc li. Hiu qu tri ngc ca hai gradient to ra chuyn ng thc ca phn t hon ton ty thuc vo nng lng t do ca hai gradient t ni c nhit cao sang ni c nng cao. 2. S thm thu hiu r bn cht ca s thm thu c th dng 2 th nghim sau. Th nghim 1: Dng mt ng hnh ch U, y c ngn cch bng mt mng thm chn lc, mng ny ch cho cc phn t nc i qua. Gi s bn A ch cha nc v bn B cha dung dch ng, c hai cng mt iu kin nhit v p sut. u tin lng cht lng hai bn tng ng nhau (hnh bn tri), hnh gia s lng cc phn t nc va chm vo mng pha bn A nhiu hn pha bn B, hnh bn phi v s phn t dch chuyn t A sang B nhiu hn t B sang A nn mc cht lng bn A tt xung trong khi bn B tng ln. S di chuyn ca mt dung mi (thng l nc) xuyn qua mt mng thm chn lc c gi l s thm thu. Lc u theo s khuch tn nc s i t bn A qua bn B, v nc tinh khit c nng lng t do cao hn nc trong dung dch ng. Nng lng t do ca cc phn t nc b gim i khi c s hin din ca nhng cht thm thu tch cc nh cc ht ha tan hay cc ht keo l lng. Trong ng hnh ch U s gim nng lng t do ca phn t nc t l vi nng thm thu. Nguyn nhn ca s gim ny l do cc ht thm thu tch cc lm mt trt t sp xp ca cc phn t nc. Do nc s i t ni c nng cao sang ni c nng thp hn. Nng thm thu ca mt dung dch l s lng ca nhng ht thm thu tch cc trn mt n v th tch dung dch. Sau mt thi gian mc cht lng bn B s cao hn trong A. Trong iu kin bnh thng mc nc ny s dng ln n mt mc no th dng li, lc ny ct cht lng c xu hng b ko xung do trng lc, do p sut thy tnh. Khi p sut ny tng, nng lng t do ca nc trong dung dch ng cng gia tng v p sut cng l mt dng ca nng lng t do, kt qu l nc s di chuyn t B qua A nhanh hn t A qua B. Khi nc i qua mng theo hai hng ngc nhau vi cng mt tc , h thng trng thi cn bng ng vi bn A c nng lng t do l tim nng thm thu ca nc tinh khit v bn B c tim nng thm thu v p sut thy tnh. Th nghim th 2 l dung dch mui c ng trong mt ng nghim, cui ng nghim c bc trong mt ti c tnh thm chn lc. Phn cui ca ng nghim cha dung dch


Tai lieu chia se tai: wWw.SinhHoc.edu.vnmui ang ng li bi s gin ra do tnh thm chn lc ca mng qua b mt ca n cho php phn t nc i qua nhng khng cho ion mui i qua (a). Khi ng nghim nhng ngp vo trong cc nc ct, mui khng th i qua mng nhng nc th c th. Nc i vo trong ng nghim lm cho dung dch mui nng ln pha trn ng nghim (b). Nc tip tc i vo trong ng nghim t cc cho n khi trng lng ca ct nc trong ng nghim nng cao ht mc cn bng vi ct nc h xung trong cc. Lc gy ra bi hin tng ny gi l s thm thu (c) (hnh 3.3).

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1 2 4

5

3

Hnh 3.3 Th nghim 2 chng minh s thm thu 1. Dung dch mui 3%; 2. Mng c tnh thm chn lc; 3. Nc ct; 4. Dung dch mui nng ln; 5. Dung dch mui ngng nng cao khi trng lng ca ct nc bng vi p sut thm thu.

II. S thm thu v mng t boMng t bo cng l mt mng thm chn lc, cc qu trnh khuch tn v thm thu l nn tng cho s sng ca t bo. Tnh thm ca mng thay i rt ln ty theo loi t bo. Th d mng ca t bo hng cu c tnh thm i vi nc cao hn trm ln so vi mng ca amip mt sinh vt n bo. 1. Tim nng thm thu v p sut thm thu Mi dung dch u c mt nng lng t do nht nh, di mt iu kin nhit v p sut nht nh, nng lng ny c th o c v c gi l tim nng thm thu. Nc tinh khit c tim nng thm thu bng khng. V tim nng thm thu gim khi nng thm thu tng nn cc dung dch c tim nng nh hn khng. Nc s di chuyn t vng c tim nng thm thu cao sang vng c tim nng thm thu thp hn. Tuy nhin, ngi ta thng c s dng khi nim p sut thm thu. p sut thm thu ca mt dung dch l gi tr ch lng nc c xu hng i vo trong dung dch bi s thm thu. Do di mt iu kin nhit v p sut nht nh, nc s di chuyn t dung dch c p sut thm thu thp sang dung dch c p sut thm thu cao khi hai dung dch c ngn cch bi mt mng thm chn lc. 2. Dung dch u trng, nhc trng v ng trng Tnh thm chn lc ca mng t bo gip cho t bo gi c cc i phn t tng hp c, nc c th thm thu qua mng t bo, do khi t t bo vo mt dung dch u trng l dung dch c nng ca cc ht thm thu tch cc cao, t bo s b co li. Nu qu lu t bo s cht. Ngc li, nu t t bo trong dung dch nhc trng, l mi trng cha nhiu nc v c t cc ht thm thu tch cc, nc s thm thu vo lm t bo phng ln v c th v ra tr khi t bo c mt c ch no c th trc xut nc ra khi t bo hay c mt cu trc c bit ngn cn s trng phng (nh hu ht t bo thc vt). T bo trong mi trng ng trng, l mi trng c s cn bng v thm thu vi t bo, v chng c cha cng mt nng cc ht thm thu tch cc, khi khng c s khc bit v lng nc i vo v i ra khi t bo. Nh vy, s lin h v thm thu gia t bo v mi trng chung quanh l mt yu t quyt nh n i sng ca t bo. Cc t bo sng trong mi


Tai lieu chia se tai: wWw.SinhHoc.edu.vntrng ng trng th s thm thu khng l vn nghim trng nh cc t bo hng cu sng trong mi trng huyt tng (hnh 3.4). Nhng mt s thc vt v ng vt sng trong cc i dng cng c nng thm thu gn nh bng vi nc bin. Cc sinh vt sng trong mi trng nc ngt th thng tch t nhiu nc trong t bo do phi c cch thi b hoc c cc cu trc gip cho n khng b trng phng ln. Tht ra s di chuyn ca nc ch l mt vn . Mng t bo cn phi kim sot s trao i qua mng rt nhiu vt cht khc nhau, do phi cn rt nhiu c ch vn chuyn khc nhau.

36

1

2

3

III. S vn chuyn vt cht qua mng t bo1. S vn chuyn th ng 1.1 Khuch tn n gin Mt cht khuch tn s khuch tn t ni c nng cao n ni c nng thp hn. Cch khuch tn ny ch ty thuc vo

4Hnh 3.4 T bo hng cu trong cc dung dch khc nhau v hin tng thm thu t bo thc vt 1. Trong dung dch u trng; 2.Trong dung dch ng trng; 3. Dung dch nhc trng; 4 S thm thu t bo thc vt

gradient nng , cng nh khng cn c s tham gia ca mt tc nhn no khc. Mt trong nhng th d quan trng l s hp thu oxy ca nhng t bo ang thc hin chc nng h hp. Oxy ha tan khuch tn vo trong t bo qua mng t bo, v s h hp tiu th oxy do s khuch tn oxy vo t bo s lin tc v gradient nng cho php s di chuyn theo hng i vo trong t bo. S khuch tn ca mt cht qua mng t bo c gi l s vn chuyn th ng bi v t bo khng tiu tn nng lng cho qu trnh ny. Trong qu trnh di chuyn cc phn t ha tan khng b bin i ha hc cng khng kt hp vi mt loi phn t no khc. Tuy nhin, do mng t bo l mng thm chn lc nn tc khuch tn bin thin theo cc loi phn t khc nhau. Vn tc ty thuc vo s chnh lch ca gradient nng v ty thuc vo vn tc khuch tn qua vng k nc ca lp lipid kp. Nc l phn t khuch tn mt cch t do xuyn qua mng, y l mt yu t rt thun li i vi i sng ca t bo, ngoi ra c mt s cht cng c khuch tn qua mng theo nh cch trn nh nhng phn t khng phn cc nh O2, N2 v nhng cht ha tan trong lipid, cn nhng cht phn cc nhng c kch thc nh nh glycerol c th i qua mng phospholipid gia cc phn t ny. 1.2 Khuch tn c tr lc Nhiu phn t phn cc v cc ion khng th khuch tn qua mng phospholipid, khi phi c s tr lc ca nhng protein vn chuyn trn mng, hin tng ny c gi l s khuch tn c tr lc (hnh 3.5). Protein vn chuyn c nhiu c im ca enzim. V c c im ca mt enzim nn chuyn bit i vi c cht ca n, mt protein mng th chuyn bit i vi mt cht m n vn chuyn v c nhng im gn c bit tng t nh hot im ca mt enzim. Ging enzim, protein vn chuyn c th b bo ha khi vn tc vn chuyn t ti protein vn


Tai lieu chia se tai: wWw.SinhHoc.edu.vnngoi t bo

37

trong t bo Hnh 3.5 S khuch tn c tr lc mc ti a mng t bo

chuyn cng c th b c ch bi nhng phn t ging nh c cht cnh tranh v gn vo protein vn chuyn. Tuy nhin, protein vn chuyn khng xc tc cc phn ng ha hc, ch xc tc cho mt qu trnh vt l gip s vn chuyn c nhanh chng. Trong nhiu trng hp protein knh c th thay i hnh dng i cht, chuyn v im gn cc cht t pha ny sang pha khc ca mng. S thay i hnh dng c tc dng nh mt lc y phng thch cht c vn chuyn (hnh 3.6).a a a

bS vn chuyn

bEnzym

bTh cm mng t bo

a

a

bXc nh vt nh du Bm cht vo t bo

bGn vo xng t bo cht

Hnh 3.6 Chc nng ca mng protein Mng protein hot ng nh l mt cht vn chuyn enzym, tt c cc vt nh du ca b mt t bo (cc cht u nhm gip vn qu trnh vn chuynl mt ci an ton) gn vo b xng ng cht no Mt kiu protein cho chuyn khc ch tt nht v knh n gin, cho php t bo cht

i qua m thi. Mt s protein hot ng nh mt knh ng m. Cc kch thch ha hc



38

hay in s lm m cc cng ny. Th d, s kch thch ca t bo thn kinh, lm m cng ca knh tr lc cho s khuch tn ca ion Na+ vo trong t bo. mt s bnh di truyn, cc h thng vn chuyn c bit c th thiu hay khng c. Th d, nh bnh cystinuria, mt bnh ca ngi l do s vng mt ca protein vn chuyn cystein v nhng acid amin khc xuyn qua mng t bo thn. T bo thn thng ti hp thu nhng acid amin ny t urin v a tr vo mu, nhng ngi mc bnh trn b au n v nhng hn si do t nhng acid amin tch t v kt tinh trong thn. Tuy c s tr lc ca cc protein vn chuyn, s khuch tn c tr lc vn l s vn chuyn th ng v cc cht vn i theo chiu ca gradient nng . Tc khuch tn ty thuc vo c ch vn chuyn ca cc protein knh nhng khng lm thay i chiu di chuyn ca cc cht c vn chuyn. Trong hnh 3.7A m t qu trnh a protein vo trong mng vng khng phn cc. Mng t bo c phn xon c ca phn t axit amni khng phn cc (mu ) dui qua lp lipid bn trong, trong khi cc protein c phn cc (mu hng) li pha ngoi ca mng 2 lp. Protein khng th chuyn vo bn trong hay ra ngoi v b ngn cch bi on protein tip xc vi nc.th mu mng li Phospholipid Vng phn cc ca protein

Protein khng phn cc

T bo cht

Cholesteron

BVng khng phn cc ca protein

Hnh 3.7 Vn chuyn protein A. Protein c a vo vng khng phn cc; B. Mt knh protein

A

Trong hnh 3.7B m t mt knh protein. y l mt mng vn chuyn protein quang tng hp ca vi khun Helobacterium balobium. Protien c chuyn vn qua mng 7 ln vi si xon khng phn cc nm gia lp lipid kp. Vng xon to thnh knh xuyn qua lp lipid kp, cc proton c bm bi th mu mng li (mu xanh). 2. S vn chuyn tch cc Mt s protein c th chuyn cc cht i ngc li gradient nng ca cht , xuyn qua mng t bo mt cht t ni c nng thp i n ni c nng cao. S vn chuyn ny tng t nh s ln dc. bm cc cht i ngc li chiu ca hng khuch tn theo gradient nng nn t bo phi s dng nng lng, v th s vn chuyn theo cch ny c gi l s vn chuyn tch cc. S vn chuyn tch cc l mt kh nng quan trng ca t bo gi li trong t bo mt cht no mt nng rt khc vi nng ca chng trong mi trng chung quanh. Th d, nu so snh vi mi trng chung quanh, mt t bo ng vt c th cha mt nng rt cao ca ion K+ v rt thp ion Na+. Mc gradient ny vn gi c l nh cc bm trn mng v ATP cung cp nng lng. ATP c th tham gia vo s vn chuyn bng cch chuyn mt gc phosphat cui cng vo protein vn chuyn. S



39

gn gc phosphat ny gy ra mt cm ng lm cho protein vn chuyn thay i hnh dng theo kiu chuyn v ni gn vo ca cc cht. Bm ion Na+ v ion K+ l mt th d v s trao i ion Na+ v ion K+ xuyn qua mng t bo ng vt (xem chng II). Mt bm sinh ra c mt hiu in th xuyn mng c gi l bm sinh in. Bm Na - K l bm sinh in chnh ca t bo ng vt. thc vt, vi khun v nm bm sinh in l bm proton, chuyn ion H+ ra khi t bo. Bm proton vn chuyn in tch dng t t bo cht ra mi trng ngoi t bo (hnh 3.8).Dch ngoi t bo

T bo cht Dng A Dng B Hnh 3.8 Bm Proton t bo thc vt Dng A

Mt loi protein vn chuyn khng phi do bm m l c kt hp s khuch tn ca mt cht vn chuyn mt cht i ngc vi gradient nng ca n. Th d, t bo thc vt dng gradient ca ion H+ c sinh ra bi bm proton ca n vn chuyn tch cc acid amin, ng v vi cht dinh dng khc vo trong t bo. Nhng protein ny c th chuyn ng vo trong t bo ngc vi gradient nng , nu n kt hp c vi ion H+, ion H+ vn chuyn theo kiu khuch tn theo gradient nng c bm ra nh bm proton. Thc vt dng cch ny ti ng sucroz c to ra bi s quang tng hp i vo trong nhng t bo ca gn l, sau ng c th c em n m libe vn chuyn n cc m khng quang hp c nh r (hnh 3.9).Ngoi t bo ng

Hnh 3.9 ng vn chuyn - mt s vn chuyn kp protein Mng t bo vn chuyn cc ion Na vo trong t bo, gradient nng ca chng h xung, cng thi im s vn chuyn phn t ng vo t bo xy ra. Gradient ng a ion Na+ cng c nng lng ln nh phn t ng cn c dng chng li gradient nng .

Bm Na-K

Vn chuyn kp protein

Trong t bo

IV. Ngoi xut bo



40

S thi ra cc i phn t (protein v polysaccharid) qua mng t bo c gi l s ngoi xut bo v s di chuyn ny theo mt c ch khc. Cc ti (bng) chuyn ch c tch ra t h Golgi c mang n mng t bo nh xng t bo cht. Khi mng ca cc ti chuyn ch v mng t bo tip xc nhau, cc phn t lipid ca mng i lipid sp xp li. Sau hai mng phi hp li v tr nn lin tc v ni dung c chuyn ch trong ti c thi ra ngoi (hnh 3.10).Sn phm tit

Mng plasma

Bng tit

T bo cht

b a

Hnh 3.10 Ngoi xut bo a) Protein v cc phn t khc c tit ra t t bo vo cc ti nh c gi l bng, bng ny cng c mng plasma gii phng cc phn t trn b mt t bo. b) nh qut hin vi in t thy c ngoi xut bo.

Nhiu t bo tit dng cch ngoi xut Phn t th th Synap bo ny thi cc sn phm ca chng. Th d, mt s t bo trong ty tng tit ra hormone insulin v a T bo chuyn chng vo mu bng s ngoi xut bo ny. Cc t bo thn kinh dng cch T bo nhn vt hnh thnh ci thch thc ngoi xut bo mt kch ti. S t bobo ch Mng plasma xy kinh protein th bo c (hnh thn ra khi khc hay tth trn mng gn vi vt liu ph hp ging nh vch, cc 3.11). Khi t bo thc vt to vic gn c cht Phn t tn hiu vi enzim. t ccvt c xngch ts thc ng ti chuyn sng carbohydrate bo thng gp ngoi t bo bo Golgi c a ra nhng mng tbch cu Hnh 3.11 S tip nhn tn hiu synaps tiu bng cch ny. cngha cc mnh vn ln hay nhng vi sinh vt (hnh 3.12b). T bo cht 5.3 Ni nhp bo qua trung gian th th V. Ni nhpnhp bo c s tham gia ca cc bo S ni Ni nhp bo bit (hnh 3.13). ly trn th th rt chuyn l cch t bo bt Gncc i phn t hay cc vt liu bng cch to ra cc ti t mng t bo. C bavi vni nhp bo l m bo, ni nhp bo qua trung gian ca th Nhn mng l nhng th th cch tr tip nhn th v thc bo ra pha ngoi ca mng. Cht chuyn bit l bn ngoi 1. m bo t bo gn vo th th c gi l a Mng plasma ligandTrong s m bo, tch phn t cngm nh dch lng bn ngoi t bo trong tng ti (mt t chung bo ung tng bit gn V im tip nhn ca mt phn t khc, nh. vo cc cht phn ln c ha tan trong cc git c a vo trong t bo nn s m t ting Latin vn c ngha l gn). Protein bo l mt kiuligarechuyn khng chuyn bit (hnh 3.12a). tip nhn thng tp hp trn mt vng ca 2. Thc bo mng, to ra mt ci lm c mt lp o T bo to Qu trnh din ra theo 4 protein bao bc. ra chn gi nybao ly vt liu l nhng mnh vt cht to hay nhng vi sinh bc sau: 1) T bo di nh hng ca ni T bo cht xut bo qua trung gian th th c phn o lm vo c protein dng mt li i vo trong t bo khi phn t ch c gn vo th Nhn th cm protein trn mng t bo; 2) Lm o xut hin trong mng plasma ca mt t bo b Hnh 3.12 m bo (a) v thc bo (b) trng ang pht trin c bao ph bi lp



41

protein (80.000 x); 3) Khi c s tp hp tng i cc phn t thch hp vo trong lm o th lm o ng li; 4) Hnh thnh ti o v chuyn cc phn t vo trong t bo.Lm o Phn t ch

Protein dng mt li

Th cm protein o ca ti kn

a

b

cHnh 3.14 Ni nhp bo quan qua trung gian th th

d



42

ngi, t bo dng cch vn chuyn ny nhn cholesterol tng hp mng hay dng tng hp ra cc steroid khc. Cholesterol trong mu di dng nhng ht nh c gi l LDL (low-density lipoprotein), mt phc hp ca lipid v protein, nh vy ligand y l LDL. Phc hp LDL gm khong 2.000 phn t cholesterol kt hp vi mt protein, protein ny c gi l apoprotein. Nhng ht nh ny gn vo th th trn mng v sau i vo bn trong t bo bng s ni nhp bo. ngi c mt bnh tn l familial hypercholesterolemia l mt bnh di truyn, vi c im l c nng cholesterol trong mu cao, l do khng c th th tip nhn LDL nn cholesterol khng vo t bo c. Cholesterol tch t trong mu, to ra hin tng m trong mu (v khi tch t nhiu lm x cng thnh ng mch).



43

S quang hpI. Khi qut v quang hp1. Nhng hiu bit u tin v s quang hp Joseph Priestley ngi Anh vo nm 1772 lm th nghim dng hai chung thy tinh, mt bn vo mt chu cy v bn kia mt con chut, sau mt thi gian c hai u cht, nhng nu chng chung vi nhau th chng u sng, th nghim ca ng cho thy cy to ra oxy, mc d lc ngi ta cha bit c cc qu trnh cng nh cha bit c vai tr chnh yu ca nh sng trong s quang hp. Trc y, cc nh khoa hc cho rng oxy c to ra trong qu trnh quang hp l t CO2, nhng ngy nay ngi ta bit rng O2 l t s phn ly ca nhng phn t nc.cy xanh 2H2O + nh sng mt tri 4 ion H+ + 4 in t + O2

ng thi ngi ta cng bit rng nng lng tch cc phn t nc l t nh sng mt tri v c dip lc t hp thu. Ion H+ t do v in t c to ra t s phn ly ca nhng phn t nc c dng bin i CO2 thnh carbohydrat v cc phn t nc mi: CO2 + 4 ion H+ + 4 in t Cy xanh (CH2O) + H2O Tm tt hai phng trnh trn: Cy xanh CO2 + 2H2O (CH2O) + H2O + O2 Mt trong nhng sn phm ca quang hp l glucoz, mt ng 6C nn c th tm tt nh sau: 6CO2 + 12 H2O nh sng, dip lc t 6O2 + C6H12O6 + 6H2O Phn ng trn phi tri qua rt nhiu phn ng, c nhng phn ng cn nh sng (pha sng) v c nhng phn ng khng cn nh sng (pha ti). 2. Bn cht ca s quang hp l mt chui cc phn ng oxy ha kh Trong khi ng l hp cht th giu nng lng th CO2 l mt hp cht ngho nng lng. Do , s quang hp khng nhng l s bin i nng lng nh sng thnh nng lng ha hc m cn d tr chng bng s tng hp cht giu nng lng. Ngi ta gi nng lng c d tr bi s kh, tc l s thm vo mt hay nhiu in t, cn qu trnh ngc li l s oxy ha, l s gii phng nng lng t mt hp cht bi s ly i mt hay nhiu in t. Trc y, khi nim ny c ngha l phn ng thm vo hay mt i oxy. Tuy nhin, hin nay t ny dng cho c nhng phn ng khng c oxy tham gia. Th d, trong nhng phn ng sinh ha hc, s dn truyn in t thng i km theo s trao i ca mt hay nhiu nguyn t hydro. Nh vy s kh l s nhn in t, d tr nng lng trong cht b kh, ngc li s oxy ha l s mt i in t, gii phng nng lng t cht b oxy ha (bng 4.1).Bng 4.1 Nhng phn ng oxy ha kh (theo McFadden)

S oxy ha - mt in t - mt hydrogen - gii phng nng lng - nhn in t - nhn hydrogen - d tr nng lng

S kh



44

Mt in t c mt phn t nhn phi l c ly i t mt phn t khc, c ngha l khi c mt cht no b kh th theo l cht khc b oxy ha. Kt qu l phn ng kh phi i cng phn ng oxy ha vi mt in t c thm vo cht ny l c ly i t cht khc nn phn ng ny c gi l phn ng oxy ha kh (redox reaction = reduction oxidation). Trong quang hp, cc phn ng oxy ha kh dng nng lng ca nh sng mt tri lm phn ly phn t nc v kh CO2 thnh dng ng giu nng lng. C ngha l, ion H+ v in t do s phn ly ca nhng phn t nc c cung cp cho CO2 to ra hp cht kh vi n v cn bn l CH2O, ng thi nng lng t nh sng mt tri c d tr trong qu trnh ny. Trong s quang hp, quan trng nht l c ch hp thu v s dng nng lng nh sng mt tri v c ch chuyn hydro v in t t nc n CO2. 3. C quan chnh ca s quang hp l l xanh S quang hp c th xy ra tt c nhng phn mu xanh, c cha dip lc t ca cy, nhng b phn chnh c cha nhiu dip lc t ca cy l l xanh, nn chng l c quan chnh ca s quang hp. Thng thng l cy gm cung l v phin l, mt s l khng c cung, phin l gn trc tip vo thn. Phin l rng, mng vi mt h gn l phc tp. Ct ngang l c th thy l c bao bc bi mt lp biu b, thng ch c mt lp t bo, c th c 2 - 3 lp hay nhiu hn. Bn ngoi biu b c bao ph bi mt lp cutin. Chc nng chnh ca biu b l bo v nhng m bn trong ca l, trnh mt nc, chng s xm nhp ca nm v cc tc nhn gy hi khc. Thng t bo biu b khng c cha lc lp nn khng c chc nng quang hp. Gia hai lp biu b l tht l, cc t bo tht l cha nhiu lc lp nn cn c gi l m lc v l l m chnh tham gia vo s quang hp ca cy. Phn tht l thng chia thnh hai tng: m lc lm thnh hng ro pha trn, gm nhng t bo hnh tr xp thng ng v m lc xp (hay m khuyt) gm nhng t bo c hnh dng khng nht nh v sp xp bt nh. Cc t bo ca c hai tng lin kt vi nhau rt lng lo, c khong trng gia chng. Nhng khong trng ny thng ra bn ngoi khng kh bi nhng l c gi l l kh (stomata). CO2 cn thit cho qu trnh quang hp t khng kh i vo l qua cc l kh ny. S ng m ca l kh c iu tit do hai t bo nm trn biu b c gi l t bo bo v (hnh 4.1 v 4.2).8 1 1 2 2 5

3 4

3 4 6 8

7

Hnh 4.1 Cu to ca l (ct ngang) 1. Tng biu b trn; 2. M du; 3. M xp; 4. Tng biu b di; 5. Cuticun; 6. T bo bo v; 7. L kh; 8. Gn l

H gn l (cc b mch) phn nhnh t cung l vo phin l lm thnh b khung cho phin l v m dn truyn l ng dn truyn chnh ni lin vi cc thnh phn khc ca cy. Mi b mch gm hai loi m chnh l m g v m libe, vn chuyn nc v cc vt



45

cht hu c i khp cy. Mi b mch thng c bao quanh bng nhng t bo bao pha ngoi. M g cung cp nc cn thit t bo tht l v sn phm cui cng l carbohydrat c chuyn n cc t bo khc trong cy nh m libe.1 2Hnh 4.2 Cu to l kh a). Nhn tng th; b) Ct dc qua tm 1. T bo biu b; 2. Vch trong mng ca t bo bo v; 3. Nhn t bo bo v; 4. L kh; 5. Lc lp; 6. T bo bo v

1 6

6

3 4

5

4. Lc lp l bo quan chnh ca s quang hp C hai mng bao bc lc lp, bn trong c cha mt h thng mng lm thnh cc ti dp thng vi nhau c gi l thylakoid. Mt s thylakoid c hnh a xp chng ln nhau nh mt chng ng xu gi l ct. Mng ngn cch gia nhng phn bn trong ca thylakoid v cht c bn ca lc lp. Nhng phn ng trong pha sng ca s quang hp xy ra trong hay trn mng thylakoid. Nhng phn ng trong pha ti ca s quang hp xy ra trong phn dch ca cht c bn bao quanh cc ti thylakoid (hnh 4.3). hiu r hn v qu trnh quang hp, ta tm hiu v cu to Chlorophyll. Chlorophyl gm mt u l phn t porphyrin v mt ui hydratcabon, phn t sc t c dng m neo hng ti vng k nc ca phn t protein gn vi mng ca thylakoid. Ch c s sai khc ca 2 phn t chlorophyll l s thay th nhm CHO (aldehyd) trong chlorophyll b bng nhm - CH3 (metyl) trong chlorophyll a (hnh 4.4).1 2 4

a

4

b

5 1

5 2 3

a

6

7

bHnh 4.3 Cu to bn trong lc lp (a), s hnh thnh ATP, NADPH ca chu trnh Calvin (b) 1. Thylakoid; 2. C cht; 3. Ct (granna); 4. H thng quang hp; 5. Ni phn ng sng; 6. Chu trnh Calvin; 3 7. Phn t cht hu c

II. Pha sng ca qu trnh quang hpPha sng ca qu trnh quang hp l gi chung cc phn ng 6trong c mt s phn ng cn s hin din ca nh sng. 1. H thng quang I v II (photosystem)4

Hnh 4.4 Lc lp (a) v Chlorophyll (b) 1. Phn t chlorophyll gn trn mng thylakoid; 2. Mng thylakoid; 3. Thylakoid; 4 Ct; 5. u Porphyrin; 6. ui hydratcarbon



46

4

Dip lc t v cc sc t ph cn thit cho qu trnh quang hp lm thnh hai h thng quang I v II, c hai u trn mng thylakoid. Mi h thng quang cha khong 300 phn t sc t, gm t 5 n 10 LHC (light-harvesting complex), mi LHC II gm ba bn n v, mi bn n v gm mt protein, 7 phn t chlorophyll a, 5 chlorophyll b v 2 carotenoid. Mi h thng quang c mt trung tm phn ng gm c 4 phn t sc t, 4 phn t enzim tt c c gn vi nhau nh mt phn t protein. Nhng phn t sc t khc hot ng nh nhng anten, hai h thng ny hp thu nng lng ca nh sng c di sng khc nhau v truyn nng lng v trung tm phn ng. H thng quang I cha phc hp trung tm phn ng P700 v n khng th hp thu nh sng c di sng cao hn 700nm, h thng quang II cha phc hp trung tm phn ng P680 v n khng th hp thu nh sng c di sng cao hn 680nm. Khi mt quang t c mt phn t sc t hp thu, nng lng c chuyn vo mt in t ca mt phn t sc t, hot ha in t ny ln mt mc nng lng cao hn. Trng thi hot ha ny c th i t phn t sc t ny sang phn t sc t khc n trung tm phn ng. Khi in t c thu nhn, phn t trung tm phn ng tr thnh mt cht c xu hng cho in t, v a in t ny n mt phn t tip nhn in t chuyn bit. Sau , in t ny c vn chuyn qua mt chui dn truyn in t. 2. Chui dn truyn in t Trong h thng quang I, phn t tip nhn in t u tin l mt protein c cha FeS. P700 b oxy ha v chuyn in t cho protein - FeS nn protein ny b kh. Sau in t t FeS c mt cht nhn in t k tip tip nhn. Trong mi chui dn truyn in t cht nhn in t tr thnh cht kh v cht cho in t thnh cht oxy ha. Cht nhn in t th hai l Fd. Cht nhn in t th ba trong chui dn truyn in t l phc hp FAD sau n chuyn in t cho NADP+ (nicotinamid adenin dinucleotid phosphat), cht ny trong c cht. Mi phn t NADP+ c th nhn hai in t t FAD v mt ion H+ t c cht ca lc lp v b kh thnh NADPH. NADPH trong c cht s l cht cho in t trong s kh CO2



47

thnh carbohydrat. Trong h thng quang II, trung tm phn ng sau khi nhn nng lng t nhng phn t sc t a ti tr thnh mt cht c xu hng cho in t mnh. Cht nhn in t u tin l Q. Q chuyn in t vo mt chui dn truyn in t, a in t t h thng quang II n h thng quang I, ni mt in t ni trn (hnh 4.5).1 1 7

5 3 4 3 2 6

H thng quang I

Phc h b6-f

H thng quang II

Kh NADP

Hnh 4.5 S AZ ca h thng quang I v II 1. Trung tm phn ng kch thch; 2. Enzym phn ly nc; 3. Trung tm phn ng; 4. Nng lng ca in t; 5. Phc h b6-f; 6. Gradient proton to thnh do s tng hp ATP; 7. Kh NADP

in t c chuyn t h thng quang II sang h thng quang I cng lc ion H+ c bm t c cht vo bn trong ti ca thylakoid. Phn t PQ va ti c in t va mang c ion H+. PQ c ng trong mng, n nhn 2 ion H+ v hai in t t mng pha bn c cht (tr thnh PQH2) v i qua pha bn kia ca mng thylakoid. Phn t dn truyn in t k tip l trong chui l cytochrom f, nhn in t t PQH2 nhng khng nhn ion H+, do ion H+ vn bn trong thylakoid. Sau in t c protein ti c ng PC (plastocyanin) chuyn n h thng quang I. Kt qu ca vic chuyn in t ny l s vn chuyn tch cc ca ion H+ t c cht vo pha trong ca thylakoid. Nng ion H+ trong thylakoid tng (pH khong 4) v bn ngoi gim i to ra mt s chnh lch v nng ion H + gia hai bn ca mng thylakoid. Hn na, mt gradient in th c sinh ra: c cht mt in tch dng, tr nn c in tch m hn v trong thylakoid c cha nhiu ion H+ tr nn c in tch dng. S khc bit v in tch v nng ion H + sinh ra gradient ha in l ngun nng lng cho s tng hp ATP. Sau khi in t t h thng quang II chuyn sang h thng quang I, th h thng quang 2 II s nhn in t t nc. H thng quang II l mt phc hp protein gm nhng sc t anten, trung tm phn ng P680 v phc hp enzim phn ly phn t nc. Phc hp enzim 1 ny c cha mt nhm gm bn ion mangan (cofactor) hot im ca n. P680 sau khi chuyn in t i tr thnh P680+ v c xu hng nhn in t mnh. P680+ vi s tr gip ca enzim phn ly nc v mt phc hp enzim Z ly in t t nc, gii phng ion H+ t do v oxy phn t (hnh 4.6 v 4.7).4 3

Tai lieu chia se tai: wWw.SinhHoc.edu.vnHnh 4.6 H thng vn chuyn in t trong quang hp 1. Mng thylakoid; 2. Phc h anten; 3. Enzym phn ly nc; 4. Gradient proton


48

3

4 5 6

1Hnh 4.7 Dn truyn in t ca vi khun lu hunh tm Khi mt in t c nng lng nh sng c y ra t trung tm phn ng ca h thng quang hp (P870), n chuyn vo chu trnh, cui cng tr li h thng quang hp t ni m n c y ra. 1. Nng lng in t; 2. Trung tm phn ng; 3. Trung tm phn ng kch thch; 4. in t chuyn bit; 5. Ferredoxin; 6. Phc h b6-f; 7. Plastocyanin

2 7

Quang tng hp

phc h b6-f

Hnh 4.6 v hnh 4.7 gii thch h thng vn chuyn in t trong quang hp: Khi photon ca nh sng p vo phn t sc t trong h thng quang II, n s kch thch in t. in t ny s ghp vi photon tr t phn t nc bi enzym v c chuyn theo chui in t cytocrom mang ca mng gii hn (vch ). Khi nc b phn ly, oxy c phng thch t t bo v ion hydro c gi li trong khong trng ca thylakoid. v tr bm proton (phc hp b6-f), nng lng cung cp bi photon c dng chuyn proton qua mng vo thylakoid. Nng ca ion hydro c trong thylakoid s c tng dn ln. Khi h thng quang hp I hp thu mt photon khc ca snh sng, sc t ca n chuyn in t nng lng cao ln th 2 cho h thng kh, iu ny lm pht sinh NADPH. Oxy l sn phm kh c gii phng, khuch tn ra khi t bo, i ra ngoi kh quyn qua kh khu. Ion H+ bn trong thylakoid v to ra gradient ha in xuyn mng. C th tm tt ng i ca in t nh sau: Nc h thng quang II chui dn truyn in t h thng quang I chui dn truyn in t th 2 NADP carbohydrat



49

Trnh t ny cho thy rng in t cn thit kh CO2 thnh carbohydrat l t nc, nhng s vn chuyn in t t nc n carbohydrat l mt qu trnh gin tip v phc tp. in t i theo mt con ng v khng thnh mt vng. Kt qu ca qu trnh l hnh thnh NADPH, gii phng oxy phn t v sinh ra mt gradient ha in xuyn mng thylakoid. 3. ATP - ngun nng lng ca t bo Phn t ATP (adenosin triphosphat) (hnh 4.8) gm adenosin ni vi ba gc phosphat l Adenosin_P P P. Cc ni gia P th nht v P th hai v ni gia P th hai v P th ba thng c gi l ni phosphat giu nng lng. Khi ni ny b thy phn thnh ADP v P s phng thch nng lng hu dng. ATP c thnh lp v thy phn trong t bo. Nu ni phosphat cui cng b thy phn th hp cht cn li l ADP (adenosin diphosphat), nu c hai ni u b thy phn th cht cn li l AMP (adenosin monophosphat). enzm ATP + H2O ADP + P + nng lng enzim ADP + P + nng lng ATP + H2O Mt ATP mi c th c thnh lp t ADP v P v c nu nng lng thnh lp cu ni phosphat vo ADP. S thm gc phospha

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