Quiz 8

Question 1

___________ are hollow tubes with walls consisting of heterodimers of α- and β- tubulin polymerized linearly into protofilaments.

Answer 1

Microtubules

Question 2

____________ are double-stranded polymers of G-actin monomers, which bind ATP.

Answer 2

Microfilaments.

Question 3

MF assembly within cells is regulated by the activity of _______________ and by the monomeric G proteins __________________.

Answer 3

Inositol phospholipids.

Rho, Rac, and Cdc42.

Question 4

_____________ are the most stable constituents of the cytoskeleton. They appear to play a structural or tension-bearing role within cells.

Answer 4

Intermediate filaments (IFs)

Question 5

____________ is a complex network of interconnected filaments and tubules that extends throughout the cytosol, from the nucleus to the inner surface of the plasma membrane.

Answer 5

Cytoskeleton.

Question 6

Microtubules are composed of the protein _________ and are about __________ in diameter.

Answer 6

Tubulin, 25 nm

Question 7

Microfilaments, with a diameter of about _________, are polymers of the protein __________.

Answer 7

7 nm, actin

Question 8

Intermediate filaments have diameters in the range of _____________ .

Answer 8

8–12 nm.

Question 9

What are the monomer subunits that make up microtubules?

Answer 9

α- and β- tubulin.

Question 10

What are the monomer subunits that make up microfilaments?

Answer 10

G-actin.

Question 11

What is the nucleotide substrate associated with microtubules?

Answer 11

GTP.

Question 12

What is the nucleotide substrate associated with microfilaments?

Answer 12

ATP.

Question 13

Originally identified in yeast, __________ are sometimes called “the fourth cytoskeleton.” They are closely associated with the contractile ring, a structure involved in the pinching off of daughter cells during cell division.

Answer 13

Septins.

Question 14

In animals, cross linked bundles of _____________ are required to maintain axons (specialized extension of nerve cells). They also form the mitotic and meiotic spindles that are essential for the movement of chromosomes during mitosis and meiosis.

Answer 14

Cytosolic MTs.

Question 15

_________________ includes the highly organized, stable microtubules found in subcellular structures specialized for cellular movement, including cilia, flagella, and the basal bodies to which these appendages are attached.

Answer 15

Axonemal MTs.

Question 16

Linear polymer of tubulin subunits; usually arranged in groups of 13 to form the wall of the microtubule.

Answer 16

Protofilament.

Question 17

Growth of microtubules by addition of tubulin heterodimers to either end.

Answer 17

Elongation.

Question 18

This is the microtubule assembly phase where, the mass of MTs increases to a point where the concentration of free tubulin becomes limiting and MT assembly is balanced by disassembly.

Answer 18

The plateau phase.

Question 19

This period reflects the relatively slow process of MT nucleation.

Answer 19

The Lag phase.

Question 20

The_________ phase of MT assembly, is the addition of tubulin dimers and it is relatively fast compared with nucleation.

Answer 20

Elongation.

Question 21

Concentration at which the rate of assembly of cytoskeletal protein subunits into a polymer is exactly balanced with the rate of disassembly.

Answer 21

Critical concentration.

Question 22

The rapidly growing end of the microtubules is called the ____________.

Answer 22

Plus end.

Question 23

The slower growing end of the microtubule is called the ______________.

Answer 23

Minus end.

Question 24

This model presumes two populations of microtubules, one growing in length by continued polymerization at plus ends and the other shrinking in length by plus-end depolymerization.

Answer 24

Dynamic Instability Model.

Question 25

This structure initiates microtubule assembly, the primary example being the centrosome.

Answer 25

Microtubule-organizing center.

Question 26

In the absence of these proteins, centrosomes can no longer nucleate MTs.

Answer 26

γ-TuRC.

Question 27

Is present in dendrites and causes the formation of looser bundles of MTs.

Answer 27

MAP2.

Question 28

This protein causes MTs to form tight bundles in axons.

Answer 28

Tau Protein.