Actin+Microtubules

Question 1

What are the 3 main parts of the cytoskeleton?

Answer 1

Actin, Microtubules and Intermediate tubules

Question 2

What is the function of the cytoskeleton?

Answer 2

Gives the cell its shape
Capacity to move or alter its shape
Organisation of organelles
Transport of organelles
Cell Division 
Chromosomes organisation and movement

Question 3

What is the actins function?

Answer 3

In the plasma membrane of animal cells to give strength and shape to the thin lipid bilayer

Question 4

What is the function of the intermediate tubules?

Answer 4

Lines the inner face of the nuclear envelope protecting DNA like a cage

Question 5

What is the function of the microtubules ?

Answer 5

Determines position of membrane bound organelles Rearrange themselves to form bipolar mitotic spindle during cell division to from cilia

Question 6

What is the abundance of the parts of the cytoskeleton?

Answer 6

In order of decreasing abundance, Microfilaments, Intermediate filaments then microtubules

Question 7

What is the 4th part of the Cytoskeleton, and its function?

Answer 7

Accessory Protein interacts w/ CS to regulate + link filaments together. Essential for controlled assembly of CS filaments at certain locations

Question 8

What are the 3 parts of the cytoskeleton made from?

Answer 8

Microfilaments and microtubules are made from subunits that can rapidly assemble and dissemble

Intermediate filaments are made of more stable fibrous protein subunits

Question 9

What is the structure of the Actin?

What domains, polymers did it have?

Answer 9

4 domains with a central cleft where divalent cation Mg2+ and nucleotide bind Helical Polymers
Flexible structure with 8nm diameter

Question 10

Mammals have how many types of actin?

Answer 10

6 types
Alpha only in muscle
Beta found with gamma

Question 11

Lower Eukaryotes like Yeast have how many actin genes?

Answer 11

One

Question 12

What is the relationship between G- actin and F-actin?

Answer 12

G-actin have 1 Ca2+ and non-covalently bound ATP

G-actin is polymerised to F-actin

Question 13

What is the shape of the actin monomer?

What is the shape/structure of the microfilament?

Answer 13

Actin monomer is pear shaped

Microfilament is polar with a plus/barbed and minus/pointed end

Question 14

What is the difference between barbed/pointed ends?

Answer 14

Barbed end grows faster and its easier for subunits to add. Pointed end requires conformational change in change in subunits

Question 15

What is the structure of the actin filament?

Answer 15

2 strands of F-actin which are twisted with 13.5 molecules per repeat 36nm
Right handed heliex

Question 16

What is the rate determining step in actin formation?

Answer 16

Nucleation

Question 17

Describe nucleation of actin polymerisation

Answer 17

Arp2 and Arp3 cannot polymerise but an ARP2/3 complex acts as a primer for the polymerisation and bind MF together

Question 18

How is actin polymerisation regulated?

Answer 18

Profilin and thymosin modulate micro filament synthesis

Question 19

How is the length of the actin micro filaments regulated?

Answer 19

Ca2+ binding to gelsolin causes cleaving of the mf
This gelosin/microfilament complex can act as a primer for cell elongation
Gelsolin is freed by PIP2 producing free + ends for rapid cell elongation

Question 20

How are the subunits in microtubules bound?

Answer 20

By covalent bonds to form a 100kDa hetrodimer/ polymerising subunit.

Question 21

What is the structure of the microtubules?

Answer 21

Tubular structure either Alpha or Beta Tublin
Alpha- GTP bound that doesnt hydrolyse
Beta- GTP may be bound so is exchangeable

Question 22

What is the Major Microtuble Organising Centre (MTOC) of animal cells?

Answer 22

In the centrosome

In the cytoplasm near the nucleus

Question 23

Describe microtuble complex of proteins

Answer 23

Mix of proteins including the gamma-tubule ring complex that nucleates the microtuble growwth.
Matrix is organised by pair of centriloes with acessory proteins .

Question 24

What drives polymerisation of the microtubules?

Answer 24

GTP hydrolysis

Question 25

What drives depolymerisation in the microtubules?

Answer 25

Release of tubulin dimers

Question 26

How is elongation in microtubules reduced?

Answer 26

Stathmin binds 2 alpha/beta tubulin dimers to reduce the elongation

Question 27

Define Dynamic Instability

Answer 27

Rapid transition between the growing state to the shrinking state of the microtubules

Question 28

What is Catastrophe in relation to microtubules?

Answer 28

Growing to shrinking state

Question 29

What is Rescue in relation to microtubule?

Answer 29

Shrinking to growing state

Question 30

What allows the cross linkages of microtubles and mediate interactions with other cellular compartments?

Answer 30

Microtubles Associated Proteins (MAPs)