Cytoskeleton

Question 1

What are the functions of the cytoskeleton?

Answer 1

Cell movement
Cell division
Muscle contraction
Vesicle transport and location of organelles
Endocytosis
Maintenance of cell shape.

Question 2

What are the 3 components of the cytoskeleton?

Answer 2

Actin filaments- made up of actin.

Intermediate fibres- fibrous proteins organised into tough, ropelike structures

Microtubules- long, hollow cylinders made up of tubulin. consists of alpha and beta tubulin.

Question 3

Give the structure of actin?

Answer 3

Structural polarity(plus and minus end)

Thinner, more flexible and shorter than microtubules.

Enriched underneath plasma membrane, although found throughout cytoplasm.

Rarely occur in isolation

Question 4

List the steps in the function of actin? ACTIN TREADMILLING

Answer 4

1. Actin monomers in the cytosol carry ATP
2. ATP is hydrolysed to ADP soon after assembly into a growing actin filament
3. Binding between ADP-bound monomers is weak meaning there is more chance of depolymerisation
4. Actin monomers are added to fast growing (+) end and fall off shrinking (–) end .

Question 5

How does the cell use actin to protude?

Answer 5

Myosin motor proteins undergo a conformational change to help pull actin filaments towards the centre of the cell(retrograde actin flow)

The cell makes use of coupling between the ECM and the actin filament to protrude

Question 6

Describe the structure of myosin?

Answer 6

Head domain (conserved) – binds actin and ATP
Tail domain (varies) – determines the specificity of the myosin

Question 7

What is the function of different myosin classes?

Answer 7

I= vesicle transport
II= Contraction
V= Organelle transport

Question 8

Give two examples of actin-binding proteins?

Answer 8

ERM, Muscle tropomyosin(muscle contraction)

Question 9

Give two examples of actin nucleators?

Answer 9

Arp2/3 complex- branched actin(molecular switch in cell)

Formins- linear actin

Question 10

What are the main 4 actin-based structures found in the cell?

Answer 10

Leading edge(lamellipodium).(for cell migration)

Cell cortex(for stability)

Filopodia(for sensing external environment)

Stress fibres.(for mechanotransduction)

Question 11

Give a summary of microtubules…

Answer 11

Tubulin heterodimers (αβ) stack on top of one another in long, straight protofilaments 13 parallel protofilaments form a rigid, hollow tube called a microtubule.

Long and relatively stiff. Microtubules have structural polarity (plus and minus end). Slow-growing minus end and fast-growing plus end
Microtubules are 25 nm in diameter. Cytoskeletal component that is mainly responsible for transporting and positioning membrane-enclosed organelles and for guiding the intracellular transport of various cytoplasmic macromolecules.

Provide structural support to cilia and flagella.
Make up the mitotic spindle – the machine for separating duplicated chromosomes.

Question 12

What does GTP stand for?

Answer 12

GTP = guanosine triphosphate

Question 13

How is the dynamic instability of microtubules controlled?

Answer 13

GTP hydrolysis.
When addition is faster is than GTP hydrolysis then a cap is formed which stabilising the microtubule for growth.

Question 14

What does a centrosome consist of?

Answer 14

pair of centrioles surrounded by matrix proteins.

The (-) end remains embedded in y-tubulin rings.

The (+) end points outwards towards the cell periphery.

Question 15

Where does tubulin polymerise from?

Answer 15

nucleation sites on a centrosome.

Question 16

What are the two microtubule motor proteins?

Answer 16

kinesins- move towards (+) end

Dyneins- move towards the (-) end of a microtubule.

Question 17

What is the arrangement of microtubules?

Answer 17

Microtubules in a cilium or flagellum are arranged in a “9+2” array.

Question 18

What does the movement of dynein cause?

Answer 18

Cilia and flagella bend.

Question 19

Give a summary of intermediate fibres…

Answer 19

Intermediate filaments, approximately 10 nm in diameter, are tough and durable components of the cytoskeleton found in the cytoplasm and nucleus.

They do not interact with motor proteins and serve various functions, including supporting the nuclear membrane, forming structural barriers like skin and nails, and helping cells withstand mechanical stress while providing structural integrity to tissues.

Question 20

Describe the assembly of intermediate fibres?

Answer 20

1. Two monomers form a parallel dimer (coiled-coil)
2. Two dimers from a staggered, anti-parallel tetramer. Polarity is lost.
3. Tetramers align end-to-end and laterally to form a protofilament
4. Pairs of protofilaments associate laterally to form a protofibril
5. Eight protofibrils wind up to form a rope-like 10 nm-thick intermediate filament

Question 21

What are the key features of intermediate fibres?

Answer 21

No structural polarity
High tensile strength

Question 22

Relate the class of intermediate fibre to its function.

Answer 22

I&II=Tissue strength and integrity in epithelial cells.

III= Sarcomere, organisation, integrity.

IV= Axon organisation in neurons.

V= Nuclear structure and organisation.

Question 23

What are the classes of intermediate filaments?

Answer 23

Intermediate filaments are divided into four main classes: keratin filaments, vimentin and vimentin-related filaments, neurofilaments and nuclear lamins.

Question 24

What is the LINC complex?

Answer 24

it links cytoplasmic cytoskeletal components to the nuclear lamina – plays an important role in mechanotransduction

Question 25

What does the LINC complex consist of?

Answer 25

The LINC complex consists of SUN and KASH proteins.

Question 26

How do intermediate fibres affect the nuclear envelope?

Answer 26

Intermediate filaments support and strengthen the nuclear envelope.

Question 27

Give two examples of diseases associated with the cytoskeleton?

Answer 27

Kartagener’s syndrome (non-motile sperm) – caused by defects in ciliary dynein. Metastasis – caused by changes in the regulation of the actin cytoskeleton.