Cytoskeleton

Question 1

What are the primary components of the cytoskeleton?

Answer 1

Microtubules

Intermediate Filaments

Microfilaments (actin)

Question 2

What protein monomers make up microtubules?

Answer 2

alpha and beta tubulin dimers

Question 3

What does it mean that microtubules display dynamic instability?

Answer 3

Microtubules go through phases of elongation that exhaust available tubulin dimers and results in depolymerization of the tubule from the - end. The newly released GDP-tubulin dimers from the - end bind new GTP and repolymerize.

Question 4

Kinesins and dyneins are motors for what skeletal structure?

Answer 4

Microtubules

Question 5

In which direction do the motor proteins of microtubules move?

Answer 5

Kinesins - towards the + end

Dyneins - towards the - end

Question 6

What structures are formed from microtubules?

Answer 6

Cilia & flagella

Question 7

What is the motor protein for actin? Which direction does it move?

Answer 7

Myosin - towards the + end

Question 8

From what structures does microtubule formation begin?

Answer 8

Microtubule Organizing Centers (MTOCs)

Question 9

Centrosomes are the sites of microtubule formation during mitosis. Which end of the microtubule extends towards the sister chromatids?

Answer 9

+ end

Question 10

What enables the cilia to move substances?

Answer 10

Dynein arms attached to the inner and outer portion of the microtubule

Question 11

What structures form the contractile ring during anaphase?

Answer 11

Actin & myosin

Question 12

What protein sequesters and regulates the actin monomer pool?

Answer 12

Profilin

Question 13

Stereocilia and microvilli are made from what cytoplasmic component?

Answer 13

Actin

Question 14

At which end do actin monomers polymerize?

Answer 14

+ end / barbed-end

ATP-actin monomers

Question 15

The - end / pointed end of actin is the site of what?

Answer 15

Depolymerization → ADP+Actin

Question 16

What proteins facilitate membrane movement through actin branching?

Answer 16

WASP.Scar & Arp⅔

(This process is highjacked by Listeria to drive intracellular motility)

Question 17

How do intermediate filaments differ from actin and microtubules in terms of function?

Answer 17

Intermediate filaments are not dynamic and are strong. They are typically used for stable cell structures

Question 18

Describe the polymerization of intermediated filaments. How does the structure differ from actin and microtubules?

Answer 18

Monomers coil together to form dimers. Dimers coil in a staggered formation to form a tetramer. Eight tetramers form an intermediate filament. The structure is polar (no +/- end) and energetically stable (does not require ATP), unlike actin and microtubules.

Question 19

What are the major classes of intermediate filaments and where can they be found?

Answer 19

• Keratins - epithelial cells
• Vimentin - cells derived from embryonic mesenchyme (fibroblasts, osteoblasts, endothelial cells, vascular smooth muscle)
• Desmin - striated and smooth muscle
• Neurofilaments - neurons
• Lamins - ubiquitously expressed

Question 20

How does the energy source for microtubule and actin polymerization differ?

Answer 20

Microtubules - GTP

Actin - ATP

Question 21

What subunits makeup actin?

Answer 21

G-actin monomers

Question 22

What drugs are used to target microtubules?

Answer 22

Colchicine

Vinblastine & vincristine

Maytansine

Taxol

Question 23

What drug prevents depolymerization of microtubules?

Answer 23

Taxol

Question 24

What drugs prevent microtubule polymerization?

Answer 24

Colchicine, vinblastine & vincristine, Maytansine