Cell Organelles
Continuous……..
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Microtubules and microfilaments
The Cytoskeleton ‫الهيكل الخلوى‬
A network of fibres ‫ شبكة من االلياف‬that provide structural support
‫ تدعيم‬to the cell. The cytoskeleton also functions in cell
motility ‫ تحرك الخلية‬and regulation
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Pages 126 - 131
The Cytoskeleton ‫الهيكل الخلوى‬
• The cytoskeleton is a network of fibers
extending throughout ‫ تمتد عبر‬the cytoplasm.
• The cytoskeleton
organizes ‫يرتب‬
the structures
and activities of
the cell.
Fig. 7.20, 126
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Cytoskeleton
Microtubules
‫أنيبيبات دقيقة‬
Thick
‫سميكة‬
Responsible for cell
motility, and
separation of
chromosome during
cell division.
(Tubulin protein)
Microfilaments
‫ألياف دقيقة‬
Intermediate
filaments
‫ألياف متوسطة‬
Thin
Middle
‫رفيعة‬
‫متوسطة‬
Support cell
motility and
transport materials
within the cell.
Reinforcing the cell
shape and fixing
position of
organelles.
(Actin protein)
(Fibrous protein)
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Page 126 - 131
5
Page 127
The Cytoskeleton ‫الهيكل الخلوى‬
• The cytoskeleton provides mechanical support and maintains
shape of the cell.
• The cytoskeleton is dynamic, dismantling ‫ يتفكك‬in one part and
reassembling ‫ يتجمع‬in another to change cell shape.
• The cytoskeleton also plays a major role in cell motility ‫ حركة الخلية‬by
interacting with motor proteins ‫البروتين الحركى‬.
– In cilia and flagella motor
proteins pull components
of the cytoskeleton past
each other ‫عكس بعضهم‬.
– This is also true
in muscle cells.
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Fig. 7.21a, Page 126
The Cytoskeleton ‫الهيكل الخلوى‬
• Interactions of motor proteins and the cytoskeleton circulates
materials within the cell.
• The cytoskeleton may transmit mechanical signals that
rearrange the nucleoli and other structures.
• Motor molecules also
carry vesicles or organelles
to various destinations
w ‫ إلى أماكن مختلفة‬provided by the
cytoskeleton.
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Fig. 7.21b, Page 126
Organelle
Motor
Protein
P
Microtubule
Energy
Microtubules functions as tracks ‫ قضيب‬that guide motor
proteins carrying organelles to their destination ‫المكان المستهدف‬.
They move chromosomes during cell division
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• In many cells, microtubules grow out from a centrosome
‫ الجسم المركزى‬near the nucleus.
• In animal cells, the centrosome has a pair of centrioles,
each with 9 triplets of microtubules ‫تسعة مجموعات كل منها مكون من ثالثة أنيبيبات‬
(9 + 0 pattern) arranged in a ring ‫ ُمرتبة دائريا‬.
• During cell division the
centrioles replicate ‫تتضاعف‬.
Fig. 7.22, Page 128
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Cilia and Flagella
• Microtubules are the central structural supports both
cilia ‫ األهداب‬and flagella ‫األسواط‬.
– Both can move unicellular and small multicellular organisms by
propelling water outside the organism.
• Cilia usually occur in large numbers on the cell surface.
• Flagella usually occur in just one or a few per cell.
• Cilia move more like oars ‫ مجادبف‬with alternating power
and recovery strokes.
• Flagella have an undulatory movement ‫حركة تموجية‬.
• So, They differ in their beating pattern ‫أسلوب الحركة‬.
Fig. 7.23, Page 129
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cilia
flagellum
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Both cilia and flagella have the same ultrastructure ‫التركيب الدقيق‬.
Both have a core ‫ مركز‬of microtubules sheathed by the plasma
membrane.
 9-doublets (9 + 2 pattern) ‫ تسعة مجموعات كل منها مكون من أنيبيبتان‬of
microtubules arranged around a pair at the center.
Flexible “wheels” of proteins connect outer doublets to each other
and to the core.
The outer doublets are
also connected by motor
proteins.
The structure of cilium
and flagellum is identical
to that of centriole.
Fig. 7.24
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• Cilia and flagella are formed of arms of a motor
protein (dynein ‫)بروتين الداينين‬.
– Dynein arms alternately
grab, move, and release
the outer microtubules.
– Protein cross-links limit
sliding and the force is
expressed as bending ‫إلتواء‬.
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Fig. 7.25
Thus, many prokaryotes are motile ‫متحركة‬
About half of all prokaryotes are capable
of directional movement ‫الحركة الموجهة‬
by the following:1.
By the flagella ‫األســواط‬, scattered ‫مبعثرة‬
over the entire surface, is the most
common ‫ شائعة‬method of movement.
2.
By two or more filaments ‫ألياف‬.
3.
By threads ‫ خيوط‬that anchors ‫ تربط‬the cells to the substratum
‫السطح الذى تعيش عليه‬.
By cilia ‫ أهداب‬that differ from flagella in beating pattern
4.
Page 529
Fig. 27.7, Page 530
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7- Cell membrane
• The plasma
membrane
functions as a
selective barrier
‫ حاجز إختيارى‬that
allows passage
of oxygen,
nutrients, and
wastes for the
whole volume of
the cell.
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Fig. 7.6, Page 113, and Fig. 7.29 Page 133
Cell membrane
Composed of lipids (phospholipids) and proteins
Lipid layer contains hydrophilic and hydrophobic regions
Carbohydrate chains
Hydrophilic ‫ُمحب للماء‬
Phospholipid
Hydrophobic ‫كاره للماء‬
Proteins
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Fig. 7.6 Page 113, and Fig. 7.29 Page 138
Comparison between Prokaryotes and Eukaryotes
Term
Prokaryotes
Eukaryotes
Size
1-10 µm in diameter
10-100 µm in diameter
Cell wall
Existed
In plant cell (not animal cell)
nucleus
No nuclear envelope but
Nucleoid
True nucleus exists with
nuclear envelope
DNA
As fibre in the nucleoid
As Chromatin (DNA and
region (plasmids in some cases) protein)
Specialized
Most of them are absent
Organells
All are existed
Cell
division
Meiotic and/or Mitotic
By Binary Fission
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