Scaffold of the cell

Question 1

What are the3 major types of protein filament in the cytoskeleton?

Answer 1

• actin microfilaments
• tubulin microfilaments
• intermediate filaments

Question 2

What are the roles of microtubules in cells?

Answer 2

• maintain cell shape
• swimming and surface movement of fluids
• formation of the mitotic spindle
• tracks for movement of vesicles organelles, proteins

Question 3

What is tubulin?

Answer 3

-a dimer made out of α and beta tubulin subunits

Question 4

What can each dimer of tubulin bind to?

Answer 4

2 GTP molecules

Question 5

What gives tubulin polarity?

Answer 5

the GTP on beta tubulin being hydrolysed

Question 6

How does the polymerisation of microtubulins occur?

Answer 6

1. tubulin monomers from dimers
2. the dimers polymerise into oligomers
3. oligomers grow into linear protonfilaments and Mts
4. MTS elongate reversibly by adding dimers. Dimers attach to both ends of Mts but preferably at + end

Question 7

what is an MTOC?

Answer 7

microtubule organising centre formed from enucleated microtubules

Question 8

How is the structure of microtubules?

Answer 8

13 Tubulin fillaments in a hollow ring

Plus end = Beta subunit
Minus end = Alpha subunit

Question 9

Describe the growth of MTs?

Answer 9

Have dynamic instability

microtubules may grow steadily and then shrink rapidly by loss of tubulin dimers from the + end

Question 10

What are the two classes of microtubule binding drugs?

Answer 10

tubulin dimer binding - Vinblastine

tubulin polymer binding - Taxol

Question 11

What does the action of the dimer binding microtubule drugs tend to be?

Answer 11

inhibit polymerisation

Question 12

What is an example of a polymer binding microtubule drug and what is its action?

Answer 12

• taxol

- favours polymerisation

Question 13

What are MT binding drugs used as?

Answer 13

• anti-mitotic agents

- anti-cancer agents

Question 14

What is taxol used to treat?

Answer 14

ovarian carcinomas and advanced breast carcinomas

Question 15

What is vinblastine/viscristine used to treat?

Answer 15

-Hodgkin’s disease
-lymphocytic lymphoma
histiocytic lymphoma
-advanced testicular cancer
-advanced breast cancer
-Kaposi’s sarcoma

Question 16

What are microtubule-associated proteins (MAPs)?

Answer 16

a family of proteins that bind to and stabilise microtubules

Question 17

What is the function of MAPs?

Answer 17

• MAPs binding speeds up polymerisation, facilitates MT assembly and stabilises the microtubules
• the other end projects outing will bind to vesicles, actin or other MTs

Question 18

What is MAP function regulated by?

Answer 18

phosphorylation

Question 19

What are some features of microtubules?

Answer 19

• thickest of cytoskeletal filaments
• 2 tubulin isoforms: alpha and beta
• GTP dependant assembly
• long hollow cylinders made up of 13 protofilaments
• dynamically unstable
• attach to microtubule organising centres
• ovement of organelles and vsicles, cell division

Question 20

What are the roles of actin filaments in cells?

Answer 20

• maintenance of cell shape
• cell movement of chemotaxis
• interaction of environment
• tracks for movement of vesicles, organelles, proteins etc

Question 21

What are the actin filament locations in cells?

Answer 21

• microvilli
• adhesion belt
• cell cortex
• filopodia
• lamellipodium
• stress fibres
• contractile ring

Question 22

What are the three types of actin?

Answer 22

α-actin
beta actin
gamma actin

Question 23

What can a monomer of actin bind to?

Answer 23

one molecule of ATP or one molecule of ADP

Question 24

How do the actin subunits arrange themselves?

Answer 24

the subunits are polar and assemble head to tail with one another

Question 25

What are the stages of actin polymerisation in vitro?

Answer 25

1. nucleation (lag phase) actin subunits form oligomers
2. elongation (growth phase) actin filaments grow
3. steady state (equilibrium phase) actin filament with subunits coming on and off

Question 26

What drugs work on actin and how do they work?

Answer 26

Phalloidin (stabilises F-actin by locking adjacent subunits together which kills the cell)

Cytochalasin (binds the barbed end of F-actin and prevents polymerisation)

Latrunculin (binds to actin monomers and prevents them from being added onto filaments)

Question 27

What does actin polymerisation provide?

Answer 27

a force for cell movement

Question 28

How is actin arranged?

Answer 28

organised into many different patterns (2D and 3D patterns)

Question 29

How many actin isoforms are there and where are they found?

Answer 29

6
4 in muscle
2 in cytoskeleton

Question 30

What are the difference in mechanical properties of IFs, AFs and MTs?

Answer 30

• MTs are deformable but unable to withstand force
• actin filaments can withstand moderate force but are not easily deformed
• IF are able to withstand high forces and are highly deformable

Question 31

What are some features of IFs?

Answer 31

-intermediate in size
-nuclear filaments-lamins
-others specific to cell type
mechanical stability-twisted coils

Question 32

What is a key concept to remember about the cytoskeleton?

Answer 32

It is dynamic