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Microtubules and microfilamentsMicrotubules and microfilamentsThe CytoskeletonThe Cytoskeleton الهيكل الهيكلالخلوىالخلوى

A network of fibresA network of fibres االلياف من that provide rovide structural structural شبكةsupportsupport تدعيمتدعيم to the cell. The cytoskeleton also functions to the cell. The cytoskeleton also functions in in cell motilitycell motility الخلية الخلية تحرك and regulationand regulation تحرك

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• The The cytoskeletoncytoskeleton is a network of fibers is a network of fibers extending throughout extending throughout عبر عبر تمتد .the cytoplasm.the cytoplasm تمتد

• The cytoskeleton The cytoskeleton organizes organizes يرتبيرتب the structures the structures and activities of and activities of the cell.the cell.

The CytoskeletonThe Cytoskeleton الخلوى الخلوى الهيكل الهيكل

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• Microtubules are the central structural supports both cilia األهداب and flagella األسواط.– Both can move unicellular and small multicellular organisms by

propelling water outside the organism.

Fig. 7.23, Page 129

Cilia and FlagellaCilia and Flagella

• CiliaCilia usually occur in large numbers on the cell surface. usually occur in large numbers on the cell surface.

• FlagellaFlagella usually occur in just one or a few per cell. usually occur in just one or a few per cell.

• CiliaCilia move more like oars move more like oars مجادبفمجادبف with alternating power with alternating power

and recovery strokes.and recovery strokes.

• FlagellaFlagella have an undulatory movement have an undulatory movement تموجية تموجية حركة ..حركة

• So, They differ in their beating patternSo, They differ in their beating pattern الحركة الحركة أسلوب ..أسلوب

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ciliacilia

flagellumflagellum

5Fig. 7.24

Both Both ciliacilia and and flagellaflagella have the same ultrastructure have the same ultrastructure الدقيق الدقيق التركيب ..التركيبBoth have a core Both have a core مركزمركز of of microtubulesmicrotubules sheathed by the plasma sheathed by the plasma

membrane. membrane. 9-doublets (9-doublets (9 + 2 9 + 2 patternpattern)) أنيبيبتان من مكون منها كل مجموعات أنيبيبتان تسعة من مكون منها كل مجموعات of of تسعة

microtubules arranged around a pair at the center. microtubules arranged around a pair at the center.Flexible “wheels” of proteins connect outer doublets to each Flexible “wheels” of proteins connect outer doublets to each

other other

and to the core. and to the core.The outer doublets are The outer doublets are

also connected by motor also connected by motor

proteins. proteins.The structureThe structure of ciliumcilium

and flagellum is identical and flagellum is identical

to that of centriole. to that of centriole.

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• CiliaCilia and and flagellaflagella are formed of arms of a motor are formed of arms of a motor protein (protein (dynein dynein الداينينالداينين بروتينبروتين ))..

– Dynein arms alternately Dynein arms alternately grab, move, and release grab, move, and release the outer microtubules.the outer microtubules.

– Protein cross-links limit Protein cross-links limit sliding and the force is sliding and the force is expressed as bending expressed as bending إلتواءإلتواء..

Fig. 7.25

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About half of all prokaryotes are capable About half of all prokaryotes are capable of directional movement of directional movement الموجهة الموجهة الحركة الحركة by the following:-by the following:-

1.1. By the By the flagellaflagella األســواطاألســواط, scattered , scattered مبعثرةمبعثرة over the entire surface, is the most over the entire surface, is the most common common شائعةشائعة method of movement.method of movement.

2.2. By two or more By two or more filaments filaments أليافألياف..

3.3. By By threadsthreads خيوطخيوط that anchors that anchors تربطتربط the cells to the the cells to the substratum substratum تعيشعليه الذى تعيشعليه السطح الذى ..السطح

4.4. By By ciliacilia أهدابأهداب that differ from flagella in beating pattern that differ from flagella in beating pattern

Thus, many prokaryotes are motileThus, many prokaryotes are motile متحركةمتحركة

Fig. 27.7, Page 530

Page 529

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7- Cell membrane7- Cell membrane

Fig. 7.6, Page 113, and Fig. 7.29 Page 133

• The plasma The plasma

membrane membrane

functions as a functions as a

selective barrier selective barrier

إختيارى إختيارى حاجز that that حاجز

allows passage allows passage

of oxygen, of oxygen,

nutrients, and nutrients, and

wastes for the wastes for the

whole volume of whole volume of

the cell.the cell.

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Cell membraneCell membrane

Composed of lipids (phospholipids) and proteinsComposed of lipids (phospholipids) and proteins

Lipid layer contains Lipid layer contains hydrophilichydrophilic and and hydrophobichydrophobic regions regions

PhospholipidPhospholipid

HydrophilicHydrophilic م5حب م5حبللماءللماء

HydrophobicHydrophobic للماء للماء كاره كاره

ProteinsProteins

Carbohydrate chains

Fig. 7.6 Page 113, and Fig. 7.29 Page 138

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Term Prokaryotes EukaryotesSize 1-10 µm in diameter 10-100 µm in diameter

Cell wall Existed In plant cell (not animal cell)

nucleusNo nuclear envelope but Nucleoid

True nucleus exists with nuclear envelope

DNAAs fibre in the nucleoid region (plasmids in some cases)

As Chromatin (DNA and

protein)

Specialized Organells

Most of them are absent All are existed

Cell division

By Binary Fission Meiotic and/or Mitotic

Comparison between Prokaryotes and EukaryotesComparison between Prokaryotes and Eukaryotes