Cytoskeleton Lecture

8/12/2019 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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Cytoskeleton Lecture

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