Lecture 17

Question 1

What are the Three types of cytoskeletal filaments:?

Answer 1

A) Microtubules
B) Microfilaments/Actin filaments
C) Intermediate filaments

Question 2

What are functions of the cytoskeleton?

Answer 2

Structural role
Motility
Cell division
Signaling

Question 3

What are actin filaments?

Answer 3

Semifelxible, polar

Question 4

What are Intermediate filaments?

Answer 4

Flexible, non-polar

Question 5

What are Microtubules?

Answer 5

stiff, polar

Question 6

What is the role of microtubules?

Answer 6

Maintains cell shape
Building block of spindle aparatus
Intracellular transport (railway track)
Motility (cilia, flagella)

Question 7

What is a microtubule unit?

Answer 7

heterodimer of alpha and beta tubuline

Question 8

How do microtubules grow?

Answer 8

Bind GTP at beta end (plus end) and hydrolyze to GDP

Question 9

What are the three phases of Microtubule self assembly?

Answer 9

Lag phase -> slow groth
growth phase (exponential growth)
plateau phase (growth is balanced)

Question 10

What happens to microtubules if GTP is depleted?

Answer 10

They dissapear rapidly

Question 11

What does Tau do to microtubules?

Answer 11

Stabilizes the microtubules -> alzheimers Tau- microtubules shrinkage)

Question 12

How is the centrosome organized?

Answer 12

consists of two centriols with pericentriolar material (PCM)

Question 13

What are functions of cilia?

Answer 13

signaling function (antenna)
flow of fluid
cellular motility

Question 14

What is the centrosome duplication cycle?

Answer 14

Centrosomes are assembled (duplicated) once per cell cycle
During mitosis the two centrosomes form the poles of the mitotic spindle , which segregates the chromosomes

Question 15

Name an MT stabilizing and destabilizing drug

Answer 15

Stabilizing: Taxol: depletes free tubulin subunits
Destabilizing: Nocodazole: inhibits MT assembly

Question 16

What are actin filaments?

Answer 16

2 filaments twisted around each other

Question 17

What is a F-actin unit?

Answer 17

globular protein that binds ATP/ADP (ATP hydrolozing activity)

Question 18

Whats special about actin comapred to MT?

Answer 18

The also polymerize to filaments but they dont spontaneously destabilize (polymerization depends on free actin conc.)

Question 19

The concentration of G-actin in the cell is 100 x greater than the critical concentration. But 40% of actin in cells
is unpolymerized. Why ?

Answer 19

Regulatory Proteins:binding actin (polymerization only occures at specific places)
Sequestration and Storage: for rapid actin polymerization (motility…)

Question 20

Cells assemble actin polymers and move faster than they can produce actin. How do they do this?

Answer 20

Actin polymerization generates force and together they multiply that force.
Treadmilling:Assembly at + end and dissassembly at - end -> recycles actin monomers for movement

Question 21

How Actin Cytoskeleton Generates Force?

Answer 21

Actin polymerization generates force, like a molecular motor. Single actin filament can generate about 5 – 10 pN force. Branched actin filament cooperate and force is 300 nN.