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Cell Organelles
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1
5)- Peroxisomes:
generate and degrade H2O2 in performing various metabolic functions
• Peroxisomes contain enzymes that transfer hydrogen from various
substrates to oxygen
– An intermediate product of this process
is hydrogen peroxide (H2O2), a poison,
but the peroxisome has another enzyme
that converts H2O2 to water.
– Some peroxisomes break fatty acids down
to smaller molecules that are transported to
mitochondria for fuel.
– Others detoxify alcohol and other harmful
compounds. Thus, it exists extensively in
the liver cells
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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
A-Microtubules & filaments
Microtubules
Thick
‫سميكة‬
Responsible for cell
motility, and
separation of
chromosome during
cell division.
(Tubulin protein)
Microfilaments
Intermediate
filaments
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
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Page 127
The Cytoskeleton ‫الهيكل الخلوى‬
Cytoskeleton provide structural support to the cell, and
also functions in cell motility and regulation
• The cytoskeleton provides mechanical support and maintains
shape of the cell.
• The cytoskeleton is dynamic, dismantling in one part and
reassembling in another to change cell shape.
• The cytoskeleton also plays a major role in cell motility by
interacting with motor proteins.
– In cilia and flagella motor
proteins pull components
of the cytoskeleton past
each other.
– This is also true
in muscle cells.
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Fig. 7.21a, Page 126
The Cytoskeleton ‫الهيكل الخلوى‬
Cytoskeleton provide structural support to the cell, and
also functions in cell motility and regulation
• 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
near the nucleus.
• In animal cells, the centrosome has a pair of centrioles,
each with nine triplets of microtubules arranged in a ring.
• During cell division the
centrioles replicate.
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
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 ‫خيوط‬.
3.
By threads ‫ خيوط‬that anchors ‫ تربط‬the cells to the substratum
‫السطح الذى تعيش عليه‬.
Page 529
Fig. 27.7, Page 530
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•
In uniform environment ‫بيئة متجانسة‬, a flagellated cell may wander
randomly.
•
In a heterogenous environment ‫بيئة مختلطة‬, many prokaryotes
are capable of taxis ‫حركة موجهة‬, movement toward or away from
a stimulus ‫عامل مؤثر‬. There are two kinds of taxis:
1.
Chemotaxis, ‫ حركة موجهة تحت تأثير كيميائى‬: movement toward the
source (positive chemotaxis) or away (negative
chemotaxis).
2.
Phototaxis ‫ حركة موجهة تحت تأثير ضوئى‬: movement toward the
source of light (negative or positive).
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7- Cell membrane
• The plasma
membrane
functions as a
selective barrier
that 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 um in diameter
10-100 um 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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