Cytoskeleton

Question 1

What is the role of the cytoskeleton?

Answer 1

Strength and support to cell
Cell shape changes
Cell movement
Cell contraction
Wound healing
Cell division
Interaction with other cells

Question 2

What are the three types of cytoskeletal filament?

Answer 2

Intermediate filaments, microtubules, actin microfilaments

Question 3

What are the main proteins of intermediate filaments?

Answer 3

Actin, vimentin and lamin

Question 4

What is the key role of intermediate filaments?

Answer 4

Provide tensile strength, by tethering cells to other cells.

Question 5

How do desmosomes work?

Answer 5

Connect cells to each other via intermediate filaments. Spread the stress points on a cell to minimise damage due to mechanical strength.

Question 6

How are intermediate filaments made?

Answer 6

Monomers of protein subunits bind to form dimers, which bind together to form staggered tetramers, which can pack together end to end. Tetramers packed together form 8 strands that twist together in a helical array.

Question 7

What is the elastic limit?

Answer 7

The maximum extent to which connected cells can stretch without permanent alteration to size or shape.

Question 8

Where are keratin intermediate filaments found?

Answer 8

Epithelial - skin, tongue, gut, nails, hair.

Question 9

Where are vimentin intermediate filaments found?

Answer 9

In connective tissue, muscle and neuroglial cells.

Question 10

Where are lamin intermediate filaments found?

Answer 10

In the nucleus.

Question 11

What happens in epidermolysis bullosa?

Answer 11

Mutations of keratin cause weak intermediate filaments, so blistering of skin occurs

Question 12

What happens in pemphigus?

Answer 12

Autoimmune condition where body’s own antibodies attack desmosomes, so contact is lost between epithelial cells and skin becomes unglued.

Question 13

How do lamins strengthen the nucleus?

Answer 13

They line the inner face of the nuclear envelope and provide attachment sites for DNA binding chromatin. They disassemble each time the cell divides.

Question 14

What happens in progeria?

Answer 14

Premature ageing disease, due to mutation in nuclear lamin A. Causes an unstable nuclear envelope, so lower capacity for tissue repair. Results in ageing, wrinkled skin, kidney failure, CV disease.

Question 15

What are microtubules made of?

Answer 15

The protein tubulin.

Question 16

What are microtubules anchored to?

Answer 16

The centrosome.

Question 17

What are the roles of microtubules?

Answer 17

Involved in cell division, anchoring organelles and intracellular transport.

Question 18

How are microtubules structured?

Answer 18

Made up of tubulin, which form dimers. Dimers combine to form a protofilament, that has polarity. 13 protofilaments combine to form a microtubule.

Grows from an organising centre, such as centrosome, spindle pore or basal body of cilium.

Question 19

How does centrosome allow microtubule growth?

Answer 19

Centrosome has gamma tubulin rings, which serve as a start site for microtubule growth. Minus end of each tubule is embedded into the centrosome, and growth occurs toward the plus end.

Question 20

How do microtubules have dynamic instability?

Answer 20

They can both grow and shrink. If growing microtubule does not attach to something in the cell, it shrinks. If microtubule attached to something in the cell, it forms a stable link with the centrosome.

Question 21

How is dynamic instability of microtubules regulated?

Answer 21

Regulated by G proteins. Tubulin are G proteins which bind to GTP - tubulin GTP forms growing microtubule. When GTP is hydrolysed to GDP, the tubule detaches and the microtubule shrinks.

Question 22

How can microtubules create polarisation of the cell?

Answer 22

They bind to capping proteins at the positive end of their filaments, and depending on the direction of growth this can lead to polarisation of the cell.

Question 23

What are cilia and flagella made of?

Answer 23

Microtubules

Question 24

Why do cancer drugs target microtubules?

Answer 24

As microtubules are involved in cell division - e.g. taxol prevents microtubules shrinking

Question 25

What are the roles of actin filaments?

Answer 25

Filaments involved in cell movement and shape, cell crawling, phagocytosis and cell division

Question 26

How is the stability of actin regulated?

Answer 26

With ATP/ADP. Actin grows with addition of an actin monomer, that causes hydrolysis of ATP. ADP remains trapped in the filament until the actin monomer dissociates from the filament.

Question 27

How does cell crawling work?

Answer 27

Actin polymerisation at the leading end of the cell pushes the cell forward, to form a new actin cortex region. Cell becomes anchored and contraction of rear end of cell draws the cell forward.

Question 28

Where is most actin in a cell concentrated?

Answer 28

Under the plasma membrane in the cell cortex. Links to proteins such as spectrum and ankyrin.