Cytoskeleton
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Transcript Cytoskeleton
Cytoskeleton
Means “cell skeleton”
Internal framework of cell
Has many functions
Anchoring cell organelles
Provide cell shape
Aids in cell motility
Response to environmental signals
Comprises
Microtubules
Microfilaments
Intermediate filaments
Microtubules
Hollow tubes made of the protein tubulin
Alternating dimers of a and b tubulin
Largest of cytoskeleton filaments
Is used for:
Maintenance of cell shape
Motility
Movement of organelles through cell
Flagella or cilia
Often involves motor molecule
Often originate from centrosome
Table 6-1a
10 µm
Column of tubulin dimers
25 nm
a
b
Tubulin dimer
Centrioles
Located in centrosome of animal cells
Occur in perpedicular pair
Have 9 triplets of microtubules
Facilitate microtubule assembly and
chromosome separation in some cells
Fig. 6-22
Centrosome
Microtubule
Centrioles
0.25 µm
Longitudinal section Microtubules Cross section
of one centriole
of the other centriole
Flagellum structure
Basal body links flagellum or cilia to cell surface
Basal body looks just like a centriole
9 +2 arrangement of microtubules
Radial spokes prevent dramatic sliding and only bending
Fig. 6-24
Outer microtubule
doublet
0.1 µm
Dynein proteins
Central
microtubule
Radial
spoke
Protein crosslinking outer
doublets
Microtubules
Plasma
membrane
(b) Cross section of
cilium
Basal body
0.5 µm
(a) Longitudinal
section of cilium
0.1 µm
Triplet
(c) Cross section of basal body
Plasma
membrane
Motor molecules
Interact with tubulin or actin
Are fixed at one end and
allowed to move freely at the
other end
Undulation-used for flagella
and cilia movement
Movement is directional
Two microtubules moving
relative to one another
Organelle movement is like a
ski lift tram or a monorail
Fig. 6-21
ATP
Vesicle
Receptor for
motor protein
Motor protein Microtubule
(ATP powered) of cytoskeleton
(a)
Microtubule
(b)
Vesicles
0.25 µm
Cell motility
Cell movement facilitated by flagella or cilia
Unlike in prokaryotes, eukaryotic flagella undulate
Cilia are small appendages and they move like a
swimmers arm-active stroke and return stroke
How cell movement works
Dynein is motor molecule that interacts with
tubulin
Dynein walks along one microtubule, while
bound to another
This results in bending
If no radial spokes or organelle coat, then
microtubules would walk out of cell
Fig. 6-25
Microtubule
doublets
ATP
Dynein
protein
(a) Effect of unrestrained dynein movement
ATP
Cross-linking proteins
inside outer doublets
Anchorage
in cell
(b) Effect of cross-linking proteins
1
3
2
(c) Wavelike motion
Microfilaments
Made of two intertwined strands of actin
Helps maintain cell shape
Actin rearrangements allow engulfment events
Psuedopod formation in ameoba
Promote cytoplasmic streaming in plants
Essential for muscle contraction
Used by invading bacteria to move around cell
Frequently being assembled and disassembled
within cell
Table 6-1b
10 µm
Actin subunit
7 nm
Microfilaments 2
Myosin interacts with actin to
cause contraction
Cytoplasmic streaming and
ameoboid motion are similar
Cortical cytoplasm around the
perimiter of cell contains
perpendicular actin (wind fence)
Streaming portion has parallel
actin which facilitates cytoplasm
movement
Plant cell wall prevents
amoeboid movement of plant cell
Intermediate Filaments
Resemble cable in structure
Are made of protein subunits
Help maintain cell shape
Are durable and not assembled and
disassembled as other cytoskeleton
components
May help maintain organelle position
Table 6-1c
5 µm
Keratin proteins
Fibrous subunit (keratins
coiled together)
8–12 nm