1

The Cell OrganellesThe Cell OrganellesThe Cell OrganellesThe Cell Organelles

عضيــات الخليـــــــــةعضيــات

الخليـــــــــة

2

• The nucleus contains most of the genes in an The nucleus contains most of the genes in an eukaryotic cell.eukaryotic cell.

• The nucleus is separated from the cytoplasm by a The nucleus is separated from the cytoplasm by a double membrane double membrane مزدوج مزدوج غشاء ..called called nuclear membranenuclear membrane غشاء

• The The nuclear membranenuclear membrane contains contains porespores ثقوبثقوب that allow that allow large macromolecules and particles to pass through.large macromolecules and particles to pass through.

• The nuclear membrane The nuclear membrane النووى النووى الغالف is maintaining the is maintaining the الغالفshape of the nucleusshape of the nucleus

1. The nucleus:1. The nucleus: Contains the cell’s genetic libraryContains the cell’s genetic library الـچينى الـچينى المحتوى المحتوى

3

Fig. 7.9, Page 116

4

• Within the nucleus, the DNA and associated proteins are organized into fibrous material, chromatinchromatin.

• In a normal cell they appear as diffuse mass.

• However when the cell prepares to divide, the chromatin fibers coil up .to be seen as separate structures, chromosomeschromosomes تلتف

• Each eukaryotic species has a characteristic number of chromosomes الكروموسومات من �ز م"َم يٍـ .رقم

- A typical human cell has 46 chromosomes, but sex cells (eggs and sperm) have only 23 chromosomes.

• Nucleolus is a dark region involved in production of ribosomes.

• The nucleus directs protein synthesis by synthesizing messenger RNA (mRNA).

– The mRNA travels to the cytoplasm and combines with ribosomes to translate its genetic message into the primary structure of a specific polypeptide.

5

• Ribosomes contain rRNA and protein.

• A ribosome is composed of two subunits وحدتين that combine تتحد to carry out protein synthesis.

2. Ribosomes :Build a cell’s proteins2. Ribosomes :Build a cell’s proteins

Fig. 7.10, Page 117

مرتبطة

حرة

6

• In the In the nucleolusnucleolus, ribosomal RNA (, ribosomal RNA (rRNArRNA) is synthesized ) is synthesized and assembled with and assembled with proteinsproteins from the cytoplasm to form from the cytoplasm to form ribosomal subunitsribosomal subunits..

• The subunits pass from the nuclear pores to the The subunits pass from the nuclear pores to the cytoplasm where they combine to form cytoplasm where they combine to form ribosomesribosomes..

• Cell types that synthesize large quantities of proteins Cell types that synthesize large quantities of proteins (e.g., pancreas) have large numbers of ribosomes(e.g., pancreas) have large numbers of ribosomes..

• Ribosomes are 2 types:-Ribosomes are 2 types:-

1.1. Free ribosomesFree ribosomes are suspended معلق in the cytosol and synthesize proteins that function within the cytosol.

2. Bound ribosomes are attached to بٍـ the outside of ملتصقthe endoplasmic reticulum.

– These synthesize proteins that are either included into membranes or for export from the cell.

B- Eukaryotic CellB- Eukaryotic Cell

3- The Endomembrane System3- The Endomembrane System

a)a) The The endoplasmic reticulumendoplasmic reticulum اإلندوبالزمية اإلندوبالزمية الشبكة manufacturers manufacturers الشبكة

membranes and performs many other biosynthetic membranes and performs many other biosynthetic

functionsfunctions

b)b) The The Golgi apparatusGolgi apparatus جولٍـچٍـى جولٍـچٍـى جهاز finishes, sorts, and ships finishes, sorts, and shipsجهاز

cell productscell products

c)c) The The LysosomesLysosomes اليسوزوماتاليسوزوماتare digestive compartmentsare digestive compartments

d)d) The The VacuolesVacuoles الفجواتالفجواتhave diverse functions in cell have diverse functions in cell

maintenancemaintenance

9Fig. 7.11, Page 119

A)- The endoplasmic reticulum manufacturers membranes A)- The endoplasmic reticulum manufacturers membranes and performs many other biosynthetic functionsand performs many other biosynthetic functions

• The ERER includes membranous tubules

• There are two types of ERER

that differ in structure and function.

1.1. Smooth ERSmooth ER looks smooth because it lacks ribosomes.

2.2. Rough ERRough ER looks rough because ribosomes (bound ribosomes) are attached to the outside, including the outside of the nuclear envelope.

• The smooth ER:The smooth ER: الناعمة اإلندوبالزمية الشبكة - It is rich in enzymes and plays a role in metabolic

processes.

- Its enzymes synthesize lipids دهون (oils, phospholipids, and steroids) including the sex hormones الهرمونات الهرمونات

.الجنسيةالجنسية - Extensive بكثرة بكثرة توجد األثر in the liver, it helps detoxify توجد األثر إبطال إبطال

السامالسام

drugs الَمخدراتالَمخدرات and poisons السَمومالسَموم

• The rough ER:The rough ER: الخشنة اإلندوبالزمية الشبكة - is especially abundant متوفرةمتوفرة in those cells that

secrete proteins as it contains ribosomes.

- These secretory proteins are packaged in transport vesicles that carry them to their next stage.

11

• Many transport vesicles ناقلة from the ER travel to the أوعيةGolgi apparatus for modification تطوير of their contents.

• The Golgi is a center of manufacturing تصنيع, warehousing تغليف, sorting تُـج هيز ( packaging), and shipping نقل materals to outside the cell.

• The Golgi apparatus is especially extensive in cells specialized for secretionspecialized for secretion إفرازية .خاليا

• The Golgi also manufactures pectin and polysaccharides.

B)- The B)- The Golgi apparatus:Golgi apparatus: finishes, sorts finishes, sorts تُـج هزتُـج هز, and ships , and ships تنقلتنقل cell productscell products

12Fig. 7.12, Page 120

وعاء ناقل

13

• The lysosomelysosome is a membrane-bounded sac of enzymes that digests macromolecules.

C)- Lysosomes C)- Lysosomes الَم"حللة الَم"حللة األجسام are digestive are digestive األجسامcomponentscomponents

Fig. 7.13a, Page 121

Lysosomal enzymes Lysosomal enzymes work best at work best at pH = 5pH = 5 ( (acidicacidic).).

The The lysosomal enzymeslysosomal enzymes are synthesized by are synthesized by rough rough ERER and then and then transferred to transferred to إلى إلى تنقل ..the the GolgiGolgi then to then to lysosomeslysosomes تنقل

Function of Lysozomal enzymesFunction of Lysozomal enzymes

1) They hydrolyse يحللproteins, fats, polysaccharides, and nucleic

acids.

2) Can destroy the cell by autodigestion (autophagy) الذاتى الذاتى الهضم .الهضم

3) Can fuse with food vacuoles الغذائية الغذائية الفحجوة to digest food, (when a الفحجوة

food item is brought into the cell by phagocytosis).

4) Can also fuse with another organelle or part of the cytosol. This

process of autophagy called recyclingrecycling which renews the cell

Lysozomal enzymesLysozomal enzymes

15

Fig. 7.14, Page 122

16

• Vesicles أوعٍـية and vacuoles فجوات are membrane-bound sacs أكياس with varied functions.

1.1. Food vacuolesFood vacuoles, from phagocytosis, fuse with lysosomes.

2.2. Contractile vacuolesContractile vacuoles, found in freshwater protists, pump excess water out of the cell.

3.3. Central vacuolesCentral vacuoles are found in many mature plant cells.

D)- Vacuoles الفجوات: Have diverse functions وظائف

الخلية in cell maintenance متنوعة على للحفاظ

17Figs. 7.15 & 166, Page 123

الفجوة الَمركذية

خلية نباتية

خلية حيوانية

18

• The membrane surrounding the central vacuole, the tonoplast, is selective النفازية in its transport of إختيارىmaterials into the central vacuole.

• The functions of the central vacuole include storing proteins or inorganic ions, depositing metabolic byproducts الثانوية األيض نواتج األصباغ storing pigments ,ترسيب

.تخزين

• It also increases internal surface of the cell.

A)- PeroxisomesA)- Peroxisomes

contain enzymes that transfer hydrogen from various substrates to contain enzymes that transfer hydrogen from various substrates to oxygenoxygen

Functions of peroxisomesFunctions of peroxisomes

1- Hydrogen peroxide (H(H22OO22) is a poison, but the peroxisome has enzyme

that converts H2O2 to water.

2- Some peroxisomes break fatty acids down to smaller molecules that are transported to mitochondria for fuel الطاقة الطاقة إلنتاج .إلنتاج

3- They detoxify ال̀سَمى الَمفعول alcohol and يبطلother harmful compounds. Thus, it exists

extensively in the liver cellsliver cells

Other Membranous Organelles

20

• Mitochondria and chloroplasts are the organelles that convert energy to

forms that cells can use for work.

• MitochondriaMitochondria are the sites of cellular respiration, generating جa ATPATP from تُـنت

the catabolism هدم of sugars, fats, and other fuels طاقة in the مصادر

presence of oxygen.

• ChloroplastsChloroplasts, found in plants and eukaryotic algae طحالب, are the site of

photosynthesis.

- They convert solar energy الشَمسية الطاقة to chemical energy and تحول

synthesize new organic compounds from CO2 and H2O.

• Mitochondria and chloroplasts are not part of the endomembrane system.

• Almost all eukaryotic cells have mitochondria.

• Mitochondria and chloroplasts are mobile and move around the cell along

tracks in the cytoskeleton.

B)- MitochondriaMitochondria: : MitochondriaMitochondria and and chloroplastschloroplasts are the main are the main energy transformers of cellsenergy transformers of cells

• MitochondriaMitochondria have a smooth outer membrane and a highly folded inner membrane forming cristae نتوءاتنتوءات.

• The inner membrane encloses the mitochondrial matrixmitochondrial matrix, a fluid-filled space with DNA, ribosomes, and enzymes.

Fig. 7.17, Page 124

22

• The chloroplastThe chloroplast produces sugar via photosynthesis.– Chloroplasts gain their color from high levels of the green

pigment chlorophyllchlorophyll.• Chloroplasts measure about 2 microns x 5 microns and are found in

leaves and other green structures of plants and in eukaryotic algae.

Fig. 7.18, Page 125

23

• The processes in the chloroplast are separated from the cytosol by two membranes.

• Inside the innermost membrane is a fluid-filled space, the stroma, in which float membranous sacs, the thylakoids.

– The stroma contains DNA, ribosomes, and enzymes for part of photosynthesis.

– The thylakoids, flattened sacs, are stacked into grana and are critical for converting light to chemical energy.

24

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 7.18