Chapter 13

Question 1

three major structural elements of cytoskeleton

Answer 1

microtubules, microfilaments, intermediate filaments

Question 2

microtubules are composed of

Answer 2

tubulin, 25nm

Question 3

microfilaments are composed of

Answer 3

actin, 7nm

Question 4

intermediate filaments are composed of

Answer 4

subunits differ depending on cell type, 8-12 nm

Question 5

microfilaments are essential components of

Answer 5

muscle fibers, cilia, flagella

Question 6

cytosolic microtubules

Answer 6

loosely organized, dynamic, responsible for variety of cellular functions

Question 7

axonemal mircotubules

Answer 7

highly organized, stable, found in subcellular structures specialized for movement

Question 8

axoneme

Answer 8

central portion of cilium or flagellum

Question 9

protofilaments

Answer 9

longitudinal arrays of linear polymers around a hollow center

Question 10

protofilaments are a

Answer 10

heterodimer of the protein tubulin

Question 11

alpha and beta tubulin have

Answer 11

1. a GTP-binding domain at N-terminus
2. a domain in the middle colchicine (poison) can bind
3. a third domain at C-terminus that interacts with MT-associated proteins

Question 12

MT is a _____ structure

Answer 12

polarized

Question 13

tubulin isoforms

Answer 13

several closely related/nonidentical cal genes for alpha and beta tubulin subunits

Question 14

singlet MT

Answer 14

13 protofilaments, full microtubule

Question 15

double, triplet MT

Answer 15

one 13 protofilament center, one/two additional incomplete tubules with 10/11 protofilaments

Question 16

where are singlets found?

Answer 16

cytosolic microtubules

Question 17

where are doublets found?

Answer 17

cilia, flagella

Question 18

where are triplets found?

Answer 18

basal bodies, centrioles

Question 19

how are microtubules formed?

Answer 19

reversible polymerization of tubulin dimers

Question 20

oligomers

Answer 20

tubulin dimers in clusters

Question 21

nucleation

Answer 21

the formation of oligomers to begin the growth of microtubules

Question 22

elongation

Answer 22

addition of subunits at either end of an oligomer

Question 23

microtubule growth depends on

Answer 23

concentration of tubulin dimers

Question 24

critical concentration

Answer 24

heterodimer concentration at which MT assembly is exactly balanced with disassembly

Question 25

plus end

Answer 25

rapidly growing end of a mircotubule

Question 26

minus end

Answer 26

the more easily disassembled end

Question 27

colchicine

Answer 27

strongly inhibits incorporation of tubulin heterodimers into mircotubules

Question 28

dynamic instability model

Answer 28

growing MT have GTP bound to their beta subunits at their plus ends while shrinking MT have GDP instead

Question 29

GTP-cap

Answer 29

provides a stable MT tip to which further dimers can be added

Question 30

microtubule-organizing center (MTOC)

Answer 30

serves as a site at which MT assembly is initiated and acts as an anchor

Question 31

centrosome

Answer 31

MTOC for cell division

Question 32

gamma Tubulin

Answer 32

a form only found in centrosomes, implicated in MT nucleation

Question 33

gamma tubulin ring complexes

Answer 33

large ring shaped structures, at base of centrosome

Question 34

microtubule-associated proteins (MAPs)

Answer 34

bind at regular intervals along walls of MT, allowing interaction with other filaments and cellular structure

Question 35

+/- TIP proteins

Answer 35

associate with MT plus ends, stabilizing

Question 36

catastrophins

Answer 36

proteins that bind to heterodimers and promote the peeling and eventual loss of subunits

Question 37

MCAK

Answer 37

mitotic centromere associated kinesin, a catastrophin

Question 38

actin

Answer 38

an extremely abundant protein in virtually all eukaryotic cells

Question 39

G-actin

Answer 39

individual actin molecules

Question 40

F-actin

Answer 40

polymerized form of G-actin into microfilaments

Question 41

“pointed” end of microfilaments

Answer 41

minus end

Question 42

“barbed” end of microfilaments

Answer 42

plus end