AM - Cytoskeleton (2)

Question 1

What do microtubules consist of?

Answer 1

α-Tubulin and β-Tubulin subunits

Question 2

How are microtubules formed?

Answer 2

• The major Microtubule Organising Centre (MTOC) is the centrosome
• y-Tubulin ring complex of the centrosome synthesises microtubule growth

Question 3

How do polymerisation and depolymerisation occur in microtubules?

Answer 3

• Polymerisation is driven by GTP hydrolysis
• Depolymerisation occurs through the release of tubulin dimers

Question 4

How is microtubule assembly regulated?

Answer 4

• Stathmin binds 2 αβ-Tubulin dimers, reducing the free pool (reduces microtubule elongation)
• Polymerisation of free tubulin subunits is energetically favourable

Question 5

How are microtubules stabilised?

Answer 5

Microtubule Associated Proteins (MAPs) allow crosslinking of microtubules- providing stability

Question 6

What are intermediate filaments?

Answer 6

They are the most stable component of the cytoskeleton and perform a structural function

Question 7

How are intermediate filaments formed?

Answer 7

Fibrous polypeptides are believed to assemble side by side to give rise to a filament with high tensile strength

Question 8

Out of IFs, MTs and MFs which are conserved and which are variable?

Answer 8

Conserved- MFs and MTs
Variable- IFs

Question 9

What are the 2 major motor proteins involved in the movement along microtubules?

Answer 9

1. KINESINS (move toward the plus end)
2. DYNEINS (move toward the minus end)

Question 10

How are microtubules important in axons?

Answer 10

Provide tracks for the movement of vesicles

Question 11

How is the directionality of movement in microtubules and microfilaments achieved?

Answer 11

Polarity

Question 12

What are 2 characteristics of motor proteins?

Answer 12

1. Globular head region- engages and moves along the filament
2. Tail region- attaches cargo to the motor protein

Question 13

What acts as the motor protein on microfilaments?

Answer 13

MYOSIN

Question 14

What is the arrangement within Cilia?

Answer 14

9 + 2 arrangement

Question 15

How does the cilium move?

Answer 15

ATP-driven movement of dynein cause microtubules within cilium to slide against each other - causes cilium to bend

Question 16

What is the role of the cytoskeleton in cell division?

Answer 16

Important in the separation of chromosomes
- Spindle fibres and contractile ring are structures of the cytoskeleton

Question 17

What allows for the indirect interaction between actin and the membrane?

Answer 17

Actin Binding Proteins (ABPs)

Question 18

What are 3 ways of cytoskeletal interactions with the membrane?

Answer 18

1. ABPs
2. Signal activation of Ezrin-Radixin-Moesin (ERM) interaction with actin
3. Binding of the cytoskeleton to the extracellular matrix via integrin

Question 19

How do mutations in dystrophin result in disorders?

Answer 19

Muscle fibres are no longer strengthened or protected- muscle becomes weaker leading to Duchenne Muscular Dystrophy (DMD)

Question 20

How do mutations in sarcoglycans result in disorders?

Answer 20

Muscle fibres are no longer connected and sarcolemma is not protected by the joining of the cytoskeleton to the extracellular matrix - muscle lacks connection resulting in Limb-Girdle
Muscular Dystrophy (LGMD)

Question 21

How do mutations in laminin result in disorders?

Answer 21

Lack of interaction with receptors anchored in the plasma membrane of cells adjacent to the basement membrane- results in Congenital Muscular Dystrophy (CMD)