in the name of allah
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• Lubert Stryer - Biochemistry
• Lehninger- Principles of Biochemistry
• Harper's -Illustrated Biochemistry
References
• Text Book of Biochemistry with clinical correlation, T M. Devlin
بیوشیمی پزشکی، هیئت مولفان ، •دانشگاه علوم پزشکی تهران، انتشارات
آییژ، دو جلد
CarbohydratesCarbohydrates
General characteristicsGeneral characteristics
Compounds composed of C, H, and O
(CH2O)n when n = 5 then C5H10O5
Not all carbohydrates have this empirical formula: Deoxysugars, Aminosugars
Carbohydrates are the most abundant compounds found in nature (cellulose: 100 billion tons annually)
General characteristicsGeneral characteristicsMost carbohydrates are found naturally in bound
form rather than as simple sugars (Glycoconjugates) Polysaccharides (starch, cellulose, inulin, gums),
Mucopolysaccharides (hyaluronic acid)
Glycoproteins and proteoglycans (hormones, blood group substances, antibodies)
Glycolipids (cerebrosides, gangliosides)
Nucleic acids (Ribose and desoxyribose)
FunctionsFunctions
Sources of energy (Glucose, Fructose,..)
Intermediates in the biosynthesis of other basic biochemical entities (Fats and proteins)
Form structural tissues in plants and in microorganisms (cellulose, lignin, murein)
Participate in cell-cell recognition, Cell-cell adhesion
Classification of carbohydratesClassification of carbohydrates
Monosaccharides (monoses or glycoses)
Oligosaccharides (condensation products of two to ten monosaccharides)
Di, tri, tetra, penta, up to 9 or 10 Most important are the disaccharides
Polysaccharides or glycans (more than 10) Homopolysaccharides Heteropolysaccharides
Classification of Monosaccharides
A. Number of carbons in chainTrioses (3C) tetroses (4C) pentoses (5C) hexoses (6C) heptoses (7C)
B. Aldose or Ketose Aldoses (e.g., glucose) have an aldehyde group at one end
Ketoses (e.g., fructose) have a keto group, usually at C2
C
C
CH2OH
OH)n(H
O
H
Aldose
C
C
CH2OH
OHH
O
H
Aldotriosen = 1
C
CH2OH
OHH
C O
H
C OHH
Aldotetrosen = 2
C
CH2OH
OHH
C O
H
C OHH
C OHH
Aldopentose n = 3
C O
H
C OHH
C OHH
CH OH
C
CH2OH
OHH
Aldohexose n = 4
Aldose sugarsAldose sugars
C
C
CH2OH
OH)n(H
O
CH2OH
Ketose
CH2OH
C O
CH2OH
Ketotriose n = 0
CH2OH
C O
C OHH
CH2OH
Ketotetrose n = 1
C OHH
CH2OH
CH2OH
C O
C OHH
Ketopentose n = 2
C OHH
CH2OH
CH2OH
C O
C OHH
OHH
Ketohexose n = 3
Ketose sugarsKetose sugars
Sugars Exhibit Various Forms of Isomerism
Aldose and Ketose isomers
L and D Isomers
Most of the monosaccharides occurring in mammals are D sugars, and the enzymes responsible for their metabolism are specific for this configuration.
1.L-arabinose 2.L-idoronic acid
D Form:
L form:
EnantiomersEnantiomers
Epimers
Two sugars that differ only in the configurationaround one carbon atom are called epimers;
Optical isomerismOptical isomerism
Asymmetric compounds rotate plane polarized light
In general, a molecule with n chiral centers can have 2n stereoisomers
Of the 16 possible aldohexoses, eight are D forms and eight are L
Most of the hexoses of living organisms are D isomers.
POLARIMETRYPOLARIMETRY
Measurement of optical activity in chiral or asymmetric molecules using plane polarized light
Measurement uses an instrument called a polarimeter (Lippich type)
Rotation is either (+) dextrorotatory or (-) levorotatory
polarimetrypolarimetry
Magnitude of rotation depends upon:
1. The nature of the compound
2. The length of the tube (cell or sample container) usually expressed in decimeters (dm)
3. The wavelength of the light source employed; usually either sodium line at 589.3 nm or mercury vapor lamp at 546.1 nm
4. Temperature of sample
5. Concentration of analyte in grams per 100 ml
[]DT
l x c observed x 100 =
D = Na+ lineT = temperature oCobs : observed rotation in degree (specify solvent)l = length of tube in decimeterc = concentration in grams/100ml[] = specific rotation
Polarimetry
Specific rotation of various Specific rotation of various carbohydrates at 20carbohydrates at 20ooCCD-glucose +52.7D-fructose -92.4D-galactose +80.2L-arabinose +104.5D-mannose +14.2D-arabinose -105.0D-xylose +18.8Lactose +55.4Sucrose +66.5Maltose+ +130.4Invert sugar -19.8Dextrin +195
In chemistry, a racemic mixture, or racemate, is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule.
Racemic mixture
A racemate is optically inactive
A racemic mixture is denoted by the prefix (±)- or dl- (for sugars the prefix DL- may be used), indicating an equal (1:1) mixture of dextro and levo isomers
Tartaric acid• It occurs naturally in many plants, particularly
grapes, bananas• Add to foods to give a sour taste• Used as an antioxidant
levotartaric acid
(D-(−)-tartaric acid)
dextrotartaric acid(L-(+)-
tartaric acid)mesotartaric acid
Structural representation of sugarsStructural representation of sugars
Fisher projection: straight chain representation
Haworth projection: simple ring in perspective
Conformational representation: chair and boat configurations
Rules for drawing Haworth projectionsRules for drawing Haworth projections
draw either a six or 5-membered ring including oxygen as one atom
most aldohexoses are six-membered
Aldotetroses, Aldopentoses, ketohexoses are five-membered
O O
Pyran Furan
Rules for drawing Haworth projectionsRules for drawing Haworth projections
Next number the ring clockwise starting next to the oxygen
If the substituent is to the right in the Fisher projection, it will be drawn down in the Haworth projection (Down-Right Rule)
O O1
23
4
5
1
23
4
Rules for drawing Haworth projectionsRules for drawing Haworth projections
For D-sugars the highest numbered carbon (furthest from the carbonyl) is drawn up. For L-sugars, it is drawn down
For D-sugars, the OH group at the anomeric position is drawn down for α and up for β. For L-sugars α is up and β is down
Formation of the two cyclic forms of D-glucose
Conformations: interconvertible without the breakage of covalent bonds, configurations :interconvertible only by breaking a covalent bond—for example, in the case of α and β configurations,
Anomers: Isomeric forms of monosaccharides that differ only in the configuration about the
hemiacetal or hemiketal carbon atom are called
Mutarotation:interconvert of The and anomes of D-glucose in aqueous solution
one-third two-thirds
<1%
Condensation reactions: acetal and ketal formation
D-ribose and other five-carbonsaccharides can form eitherfuranose or pyranose structures
Chair and boat conformations of a pyranose sugar
2 possible chair conformationsof -D-glucose
Envelope Conformations of β - D-ribose
Envelope Conformations
Oxidation reactionsOxidation reactionsAldoses may be oxidized to 3 types of acids
◦Aldonic acids: aldehyde group is converted to a carboxyl group ( glucose – gluconic acid)
◦Uronic acids: aldehyde is left intact and primary alcohol at the other end is oxidized to COOH Glucose --- glucuronic acid Galactose --- galacturonic acid
◦Saccharic acids: (glycaric acids) – oxidation at both ends of monosaccharide) Glucose ---- saccharic acid Galactose --- mucic acid Mannose --- mannaric acid
Solutions of cupric ion (known as Fehling's solution) provide a simple test for sugars such as glucose. Sugars that react are called reducing sugars; those that do not are called nonreducing sugars
ReductionReduction
either done catalytically (hydrogen and a catalyst) or enzymatically
the resultant product is a polyol or sugar alcohol (alditol)
glucose form sorbitol (glucitol)mannose forms mannitolfructose forms a mixture of sorbitolglyceraldehyde gives glycerol
Sructures of some sugar alcohols
used as a sugar substitute in foods, especially for diabetics. In cosmetics it is commonly used in aftershave lotions, mild soaps and baby shampoos. Sorbitol is used as a humectant and skin conditioning agent
Special monosaccharides: deoxy sugarsSpecial monosaccharides: deoxy sugars
These are monosaccharides which lack one or more hydroxyl groups on the molecule
one quite ubiquitous deoxy sugar is 2’-deoxy ribose which is the sugar found in DNA
6-deoxy-L-mannose (L-rhamnose) is used as a fermentative reagent in bacteriology
examples of deoxysugars
Several sugar esters importantin metabolism
Special monosaccharides: amino sugarsConstituents of mucopolysaccharides
The anomeric forms ofmethyl-D-glucoside
PropertiesProperties
Differences in structuresDifferences in structures of sugars are responsible for of sugars are responsible for variations in propertiesvariations in properties
Physical Crystalline form; solubility; rotatory power
Chemical Reactions (oxidations, reductions, condensations)
Physiological Nutritive value (human, bacterial); sweetness; absorption
OligosaccharidesOligosaccharides
Most common are the disaccharides
Sucrose, lactose, maltose, terehalose Maltose : 2 molecules of D-glucose
Lactose : glucose + galactose
Sucrose : glucose + fructose
Terehalose : 2 molecules of D-glucose
SucroseSucrose
α-D-glucopyranoside + β-D-fructofuranoside
commercially obtained from sugar cane or sugar beet
hydrolysis yield glucose and fructose (invert sugar) (sucrose: +66.5o ; glucose +52.5o; fructose –92o)
used pharmaceutically to make syrups
Sugar cane
Sugar beet
Sources of sucrose
Non reducing sugar
Structure of sucrose
LactoseLactose
β-D-galactose (β 1,4) α-D-glucose
used in infant formulations, medium for penicillin production and as a diluent in pharmaceuticals
Reducing sugar
MaltoseMaltose
2-glucose molecules joined via α(1,4) linkage
known as malt sugar
produced by the partial hydrolysis of starch (either salivary amylase or pancreatic amylase)
used as a nutrient (malt extract; Hordeum vulgare); as a sweetener and as a fermentative reagent
reducing sugar
Structure of maltose
Glc(α1 4)Glc
Trehalose
Non reducing sugar
LactuloseLactuloseGalactose-β-(1,4)-fructose
A semi-synthetic disaccharide (not naturally occurring)
Not absorbed in the GI tract
Used either as a laxative
Metabolized in distal ileum and colon by bacteria to lactic acid, formic acid and acetic acid (remove ammonia)
OligosaccharidesOligosaccharides
Trisaccharide: raffinose (glucose, galactose and fructose)
Tetrasaccharide: stachyose (2 galactoses, glucose and fructose)
Pentasaccharide: verbascose (3 galactoses, glucose and fructose)
Raffinose can be hydrolyzed to D-galactose and sucrose by the enzyme α-galactosidase (α-GAL), an enzyme not found in the human digestive tract.
α-GAL also hydrolyzes other α-galactosides such as stachyose, verbascose, and galactinol, if present. The enzyme does not cleave β-linked galactose, as in lactose.
raffinose
stachyose (2 galactoses, glucose and fructose)
verbascose (3 galactoses, glucose and fructose)
Polysaccharides or glycansPolysaccharides or glycans
homoglycans (starch, cellulose, glycogen, inulin)
heteroglycans (mucopolysaccharides)
characteristics: polymers (MW from 200,000) White and amorphous products (glassy) not sweet not reducing; do not give the typical aldose or ketose
reactions) form colloidal solutions or suspensions
Homoglycans
StarchStarch
most common storage polysaccharide in plants
composed of 10 – 30% a-amylose and 70-90% amylopectin depending on the source
the chains are of varying length, having molecular weights from several thousands to half a million
Amylose and amylopectin are the 2 forms of starch. Amylopectinis a highly branched structure, with branches occurring every 12to 30 residues
Amylose and amylopectin, the polysaccharides of starch
amylopectinStrands of amylopectin form double helical
structures with each other or with amylose strands
Salivary amylase : Salivary amylase : αα (1-4) endoglycosidase (1-4) endoglycosidase
GGG G
G
G G G 1-4 linkG
GGG 1-6 link
GG
G
GG G G G G
GG
G
G G
G
maltose
G
GG
isomaltose
amylase
maltotriose
G
G
G
G
Limit dextrins
DextrinsDextrins
produced by the partial hydrolysis of starch along with maltose and glucose
used as mucilages (glues)
also used in infant formulas (prevent the curdling of milk in baby’s stomach)
CelluloseCellulose
Polymer of β-D-glucose attached β) linkages
Yields glucose upon complete hydrolysis
Partial hydrolysis yields cellobiose
Most abundant of all carbohydrates Cotton flax: 97-99% cellulose Wood: ~ 50% cellulose
The structure of cellulose(linear, unbranched homopolysaccharide)
Structure of cellulose
GlycogenGlycogenalso known as animal starch
stored in muscle and liver
present in cells as granules (high MW)
contains both a(1,4) links and a(1,6) branches at every 8 to 12 glucose unit
complete hydrolysis yields glucose
hydrolyzed by both a and b-amylases and by glycogen phosphorylase
InulinInulin
β-(1,2) linked fructofuranoses
linear only; no branching
lower molecular weight than starch
hydrolysis yields fructose
sources include onions, garlic, dandelions and jerusalem artichokes
used as diagnostic agent for the evaluation of glomerular filtration rate (renal function test)
Jerusalem artichokes
ChitinChitin
Chitin is the second most abundant carbohydrate polymer
Present in the cell wall of fungi and in the exoskeletons of crustaceans, insects and spiders
Chitin is used commercially in coatings (extends the shelf life of fruits and meats)
Heteropolysacharides
Glycosaminoglycans Glycosaminoglycans (Mucopolysacharides)(Mucopolysacharides)
they are the polysaccharide chains of proteoglycansthey are linked to the protein core via a serine or
threonine (O-linked)the chains are linear (unbranched)the glycosaminoglycan chains are long (over 100
monosaccharides)they are composed of repeating disaccharides
GlycosaminoglycansInvolved in a variety of extracellular functions; chondroitinis found in tendons, cartilage and other connective tissues
Glycosaminoglycans
A characteristic of glycosaminoglycans is the presenceof acidic functionalities (carboxylate and/or sulfates)
Glycosaminoglycans
Proteoglycans are glycosaminoglycan-containing macromolecules of the cell surface and extracellular matrix
Proteoglycan structure
Some proteoglycans can form proteoglycan aggregates
Proteoglycan aggregate of the extracellular matrix
Aggrecan interacts strongly with collagen in the extracellular
matrix of cartilage, contributingto the development and tensile
strength of this connective tissue
Proteoglycans are a family of glycoproteins whose carbohydrate moieties are predominantly glycosaminoglycans
structures are quite diverse as are sizes examples: versican, serglycin, decorin, syndecan
Functions: - modulate cell growth processes - provide flexibility and resiliency to cartilage
Hyaluronate:material used to cement the cells into a tissue
Interactions between cells and the extracellular matrix
Cross-linked meshwork that gives the whole
extracellular matrix strengthand resilience
Bacterial cell wallBacterial cell wall
provide strength and rigidity for the organism
consists of a polypeptide-polysaccharide known as petidoglycan or murein
determines the Gram staining characteristic of the bacteria
Structure of peptidoglycan
Structure of peptidoglycan
Cell wall of Gram-positive bacteria
Gram-negative bacteria
Cross-section of the cellwall of a gram-negativeorganism such as E.coli
Lipopolysaccharide (LPS) coats theouter membrane of Gram-negativebacteria.
the lipid portion of the LPS is embedded in the outer membrane and is linked to a complex polysaccharide
Lipopolysaccharide
Glycoproteins (Mucoprotins)Glycoproteins (Mucoprotins)
Usually done as a post-translational process
Proteins can contain either O-linked oligosaccharides or N-linked oligosaccharides
Serine or threonine O-linked saccharides
Aspargine N-linked glycoproteins
Roles of oligosaccharides in recognition and adhesion at the cell surface
Complex structure (branching, stereoisomerism)
•Hexasaccharid: 1.05*1012, hexapeptide: 4096, hexanucleotide: 6.4*107
Clone, Expresion, PCR-amplification
Sequencing
synthesis
Lectins are glycoproteins that recognize and bind to specific oligosaccharides.
Recognition/binding of CHO moieties of glycoproteins, glycolipids & proteoglycans by animal lectins is a factor in:
cell-cell recognition adhesion of cells to the extracellular matrix recognition of disease-causing microorganisms initiation and control of inflammation.
Lectins
Glycome:
Glycomics:
•to describe the complete rang of oligosaccharide sequences that can be found in a cell type, organ or organism
•study of glycome by glycoarray
Glycoarray
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