The cytoskeleton

Question 1

What are the main functions of the cytoskeleton?

Answer 1

Keeps the cell shape
Cell movement
Providing mechanical strength
Chromosome separation

Question 2

Why is the cytoskeleton dynamic?

Answer 2

There are a lot of monomers which are NOT covalently bonded and this makes it easier to disassemble.

Question 3

What is the function of accessory proteins in the cytoskeleton?

Answer 3

Regulate site and rate of filament formation, de and polymerisation and function.

Question 4

What is the structure of intermediate filaments?

Answer 4

Rope like fibres. 8 tetramers twisted into rope like filament.

Question 5

What is the function of intermediate filaments?

Answer 5

Maintain cell structure and provide tensile strength

Question 6

What are the functions of cytoplasmic intermediate filaments?

Answer 6

Keratins found in epithelial cells which are hard, waterproof and resist abrasions. Vimentins found in muscles which provide mechanical strength. Neurofilaments which strengthen the axon.

Question 7

What is the function of nuclear intermediate filaments?

Answer 7

Form nuclear lamins which stabilise the inner nuclear membrane of cells. Strengthen and provide attachment sites for chromatin in nuclear envelope.

Question 8

What are desmosomes?

Answer 8

Intercellular junctions which bind intermediate filaments to the plasma membrane.

Question 9

What is epithelial transmigration and what cytoplasmic intermediate filament is involved?

Answer 9

White blood cells having to leave the blood stream to combat infection. Vimentin allows the cell to squeeze out deform and then reform once it has crossed.

Question 10

What is the protein desmin?

Answer 10

It maintains muscle structural integrity and tethers to Z disk in muscles. It does NOT participate in contraction.

Question 11

What are some examples of intermediate filament binding proteins?

Answer 11

Fillagrin which binds keratin filaments into bundles. Plakins which keep the contact between desmosomes of epithelial cells.

Question 12

What is the structure of microtubules?

Answer 12

Long hollow cylinders made of tubulin.

Question 13

How many isoforms does tubulin have? Which isoforms form microtubules?

Answer 13

3, alpha, beta and gamma. Only alpha and beta together form microtubules.

Question 14

What are the main functions of microtubules?

Answer 14

Establish structure in interphase cells, involved in intracellular trafficking, coordinate migration of chromosomes, participate in motility via cilia/flagella.

Question 15

What is elongation and shrinkage of microtubules?

Answer 15

Elongation is addition of tubulin at the + end due to GTP and shrinkage is loss of tubulin at - end due to GDP.

Question 16

Why are microtubules dynamically unstable?

Answer 16

Total mass of polymerised tubulin remains constant. INDIVIDUAL microtubules are dynamic as they change depending on the cells needs.

Question 17

What are catastrophe and rescue?

Answer 17

Catastrophe is switching from growth to shrinkage. Rescue is the opposite.

Question 18

What is the centrosome?

Answer 18

The major microtubules-organising centre which is compromised of 2 centrioles. Structure is involved in process of cell division.

Question 19

What are MAPs?

Answer 19

Microtubule-associated proteins, function as cross-bridges connecting microtubules. They affect microtubules rigidity and assembly rate.

Question 20

What are motor proteins?

Answer 20

Enzymes which convert ATP hydrolysis into movement along cytoskeletal filaments. Some will move to + while others will move to - end.

Question 21

What is kinesis?

Answer 21

Motor protein which moves cargo to the + end. Involved in mitotic spindle dynamics.

Question 22

What is dyneins?

Answer 22

Motor protein which moves cargo to -. Involved in beating of cilia and flagella and involved in mitotic spindle dynamics.

Question 23

What is a part of the complex which facilitates carrying?

Answer 23

Vesicle, ankyrin, dynein, spectre and dynactin complex.

Question 24

What are the 2 classes of dynein and their functions?

Answer 24

Cytoplasmic dynein, carries cargo in cytoplasm and involved in mitotic spindle dynamics. Axonemal dyneins, in cilia and flagella.

Question 25

What is the motile axonome?

Answer 25

Foundation of flagella structure and function. Forms series of duplexes of microtubules and has a central singlet microtubules which controls how flagella moves.

Question 26

What is the structure of microfilaments?

Answer 26

Two-stranded helical polymers of actin, less rigid than microtubules. Found dispersed in the cell mostly concentrated at the cortex beneath plasma membrane.

Question 27

What are the functions of microfilaments?

Answer 27

Provide mechanical strength, form contractile ring, role in cell motility and migration and interact with myosin motors to provide muscle contraction.

Question 28

What are actin-binding proteins?

Answer 28

Proteins which govern actin architecture and function . e.g. tropomyosin.

Question 29

What happens when there is polymerisation at the front of the cell?

Answer 29

This pushes the cell forward and allows intracellular movement.

Question 30

What are ARP complexes?

Answer 30

Initiate nucleation of new actin filament which can mature. Nucleate filaments more efficiently when it is bound to side of pre existing filaments.

Question 31

How do we control the actin monomers?

Answer 31

Actin is not polymerised as it is bound to proteins like thymosin allowing them to become LOCKED and cannot associated with the ends.

Question 32

How do actin monomers escape thymosin?

Answer 32

Dependent on profilin which binds to part of actin opposite the ATP binding cleft. This can bind to the + end of actin filament.

Question 33

What is the role of tropomyosin?

Answer 33

Stabilizes by bidding to 7 adjacent actin subunits in one filament and prevents other proteins from binding to actin.

Question 34

What is cofilin?

Answer 34

Destabilizes the actin filaments by forcing it to twist.