Cytoskeleton Lecture
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Transcript of Cytoskeleton Lecture
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Cytoskeleton
Dr Ashok Patel
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Further reading
Brooker: chapter 4.3, pages 73-76
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CELLS CAN:
Adopt a variety of shapes
Carry out co-ordinated movement
Organise many components in the cytoplasm
Interact mechanically with environment
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CYTOSKELETON
Highly dynamic structure that is constantly
reorganised as a cell changes shape, divides,and responds to its environment
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The interior of the cell is in constant motion andthe cytoskeleton provides the machinery for:
Intracellular movements such as the transportof organelles
The segregation of chromosomes into daughtercells at mitosis
Pinching apart of animal cells at cell division
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Cytoskeleton is also responsible for large-scalemovements such as crawling of cells along a
surface, contraction of muscle cells, and the
changes in cell shape that take place as anembryo grows
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Cell Movement
Some cells crawl!
Essential for inflammation, clotting, woundhealing, and the spread of cancer
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Cell Movement
Other cells have cilia.
Short cellular processes often arranged in rows.
In several tissues the beating of cilia is an
important process. The sensory cells of the
vertebrate ear also contain cilia.
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Cytoskeleton
Actin filaments (microfilaments)
Microtubules
Intermediate filaments
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Cytoskeleton
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Actin filament: made of two strands of fibrous protein actin
twisted together. Usually occur in bundles
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Microtubules: composed of tubulin protein subunits
arranged side by side to form a tube
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Intermediate filaments: composed of overlapping staggered
tetramers of protein
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Microtubules, the thickest fibers, are hollow rods
about 25 microns in diameter.
Microtubule fibers are constructed of the globular
protein, tubulin, and they grow or shrink as more
tubulin molecules are added or removed.
They move chromosomes during cell division.
Another function isas tracks that guide
motor proteins
carrying organelles
to their destination.
Fig. 7.21b
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In many cells, microtubules grow out from a
centrosome near the nucleus.
These microtubules resist compression to the cell.
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Fig. 7.22
In animal cells, the centrosome has a pair ofcentrioles, each with nine triplets ofmicrotubules arranged in a ring.
During cell division thecentrioles replicate.
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Microtubules are the central structural supports in
cilia and flagella.
Both can move unicellular and small multicellular
organisms by propelling water past the organism.
If these structures are anchored in a large
structure, they move fluid over a surface.
For example, cilia sweep mucus carrying trappeddebris from the lungs.
Fig. 7.2
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Actin filaments
Play a fundamental role in cell movement
Pseudopodia, cellular extensions, extend and
contract through the reversible assembly and
contraction of actin subunits
A contracting belt of microfilaments divides the
cytoplasm of animals cells during cell division
(cytokinesis)
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Cell migration
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Animation: cell_motility.swf
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intermediate in size at 8 - 12
nanometers, are specialized forbearing tension.
Intermediate filaments arebuilt from a diverse class of
subunits from a family ofproteins called keratins.
Intermediate filaments are morepermanent fixtures of thecytoskeleton than are the othertwo classes.
They reinforce cell shape and fixorganelle location.
Intermediate Filaments
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Besides the shape and movement of a cell,
the cytoskeleton provides a scaffold to hold
certain organelles and enzymes in defined
areas of the cytoplasm
Cytoskeleton organises the cells activities by
moving organelles and enzymes
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Energy requiring motor proteins calledIntracellular Molecular Motors are neededfor movement of organelles within the cell
Kinesin
Dynein
Movement in opposite directions
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Fig. 5.26 (TEArt)
Microtubule
Vesicle
Dynactincomplex Dynein
Otherassociated
proteins
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Fig. 6.5 (TEArt)Extracellular fluid
CarbohydrateGlycolipid
Transmembraneproteins
Glycoprotein
Peripheralprotein
Cholesterol
Filaments ofcytoskeleton
Cytoplasm
Extracellularmatrix protein
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The cytoskeleton is composed of:1. Microtubules and strong
prolactin filaments2. Intermediate filaments,
microtubules and actin
filaments
3. Endothelial filaments,
minitubules and actin
filaments
4. A matrix of intermediatefilaments covered with actin
5. Many dozens of filaments
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Which of the following is FALSE?1. Actin filaments are made of two
strands of actin twisted together
2. Microtubules are composed of
tubulin protein subunits
arranged to form a tube
3. Intermediate filaments is
composed of overlappingstaggered tetramers of protein
4. Actin filaments usually occur in
bundles
5. To increase strength actinfilaments are converted into
microtubules when needed by
the cell
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------- and ------- are intracellular motors
which help move organelles within the cell
1. Kinein and Dynesin
2. Kinesin and Dynein
3. Kinetin and Dysine4. Kinetic and Didedine
5. Kinin and Dinin
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