Question 1

Microtubules are typically _______ in diameter. 25 nm 10-12 nm 25 mm 35 nm 7 nm

Accepted Answer

25 nm

Question 2

According to the current model, which of the following is the correct sequence of microtubule assembly?  dimers, oligomers, sheets of protofilaments, protofilaments, closing of microtubule, elongating microtubule dimers, sheets of protofilaments, closing of microtubule, oligomers, protofilaments, elongating microtubule dimers, oligomers, protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule, dimers, oligomers dimers, oligomers, protofilaments, elongating microtubule, sheets of protofilaments, closing of microtubule

Accepted Answer

dimers, oligomers, protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule

Question 3

Which of the following is not a cellular activity associated with microtubules? maintenance of axons maintenance of cell shape cytokinesis of animal cells axonemal structure formation of mitotic spindle

Accepted Answer

cytokinesis of animal cells

Question 4

Which stage of microtubule assembly is the stage in which nucleation occurs?  sheets of protofilaments closing of microtubules oligomers dimers elongation

Accepted Answer

oligomers

Question 5

Tubulin may assemble and disassemble simultaneously in a process known as  dynamic instability. treadmilling. microtubule organizing. MAP motoring. actin-regulated assembly.

Accepted Answer

treadmilling.

Question 6

Microtubules have an inner diameter of ________ and an outer diameter of ________.  15 mm; 25 mm 8 nm; 12 nm 25 nm; 30 nm 15 nm; 25 nm 7 mm; 14 mm

Accepted Answer

25 nm; 30 nm

Question 7

Which one of the following statements about microtubules is correct?Microtubules: are static structures within a cell. are made up of tubulin heterotetramers. require ATP hydrolysis for growth. are made up of 13 linear protofilaments. are symmetrical rather than polar structures.

Accepted Answer

are made up of 13 linear protofilaments.

Question 8

Critical concentration is  the concentration of tubulin dimers at which assembly is balanced with disassembly. the concentration of tubulin dimers at which assembly occurs primarily. the concentration of G-actin in most muscle cells. required before nucleation can occur. both choices A and D

Accepted Answer

the concentration of tubulin dimers at which assembly is balanced with disassembly.

Question 9

Which one of the following statements about dynamic instability of microtubules is correct? Dynamic instability: describes the behavior of the stock market in economics. describes the alternating cycles of growth and shrinkage in microtubules. was first shown by Watson and Crick in 1952. describes the growth of microtubules when the concentration of GTP-bound tubulin is low. describes the frequent cleavage of microtubules near the middle of its length.

Accepted Answer

describes the alternating cycles of growth and shrinkage in microtubules.

Question 10

The minus (-) ends of microtubules are often anchored at the ________________ , such that the dynamics associated with microtubules is at the plus (+) ends.  centriole centrosome plasma membrane centromere mitochondrial outer membrane

Accepted Answer

centrosome

Question 11

microtubules are composed of

Accepted Answer

tubulin dimers

Question 12

tubulin dimers are

Accepted Answer

composed of a-tubulin (minus end) and b-tubulin (plus end)polymerized from head to tail to form filaments

Question 13

microtubules grow

Accepted Answer

faster at the plus end then the minus endfrom the MTOC

Question 14

MTOC

Accepted Answer

microtubule organizing center in plant and animal cells, contains centrosomehas limited number of nucleation and anchorage sites, has most during prophase and prometaphasewhere minus end is anchored

Question 15

microtubules

Accepted Answer

provide stability and are involved in movement, help cell resist compression forces, provide structural framework for organellesare necessary, without them ER would collapse and golgi would disappearused in mitosis and meiosiscan form as singlets (1 MT made of 13 protofilaments)can form doubles (13 protofilament A tubule, 10-11 protofilament B tubule) in cilia and flagella can form triplets (13 protofilament A tubule, 10-11 protofilament B and C tubule) in basal bodies and centrioles

Question 16

centrosome

Accepted Answer

has 2 perpendicular centrioles which are bundles of microtubules has pericentriolar matrix where microtubules originate from

Question 17

cytoplasmic microtubules

Accepted Answer

loosely organized, dynamicvisualized with fluorescence microscopy in animal cells: maintain axons, extend nerve cells, maintain polarized shape of migrating cells from inside the cytoplasmin plant cells: govern orientation of cellulose microfibrils deposited during growth of cell wallboth: form mitotic and meiotic spindles used to move chromosomes, contribute to movement and distribution of vesicles and other organelles by providing a system of fibers

Question 18

axonemal microtubules

Accepted Answer

highly organized, stableassociated with movement: cilia, flagella, basal bodies where these appendages attachmake up central shaft (axoneme) of cilia and flagellafirst to be discovered and studied

Question 19

protofilaments

Accepted Answer

13 of these are arranged side by side to for MT

Question 20

tubulin

Accepted Answer

both b and a tubulin have GTP binding site, domain for colchicine to bind, and C-terminus that interacts with proteins (MAPs)can be different isoforms (interact with different proteins)can be chemically modified (acetylated tubular forms more stable MTs than non-acetylated tubulin)

Question 21

nucleation

Accepted Answer

the aggregation of tubulin dimers into clusters called oligomers which serve as nuclei from which new MTs can growsignificant concentration of tubulin dimers, GTP, and Mg2+ needed to occurknown as lag phase, which takes a long time

Question 22

elongation

Accepted Answer

the polymerization of microtubuleshappens quickly until point when free tubulin becomes limiting

Question 23

plateau phase

Accepted Answer

when MT assembly and disassembly are balanced

Question 24

critical concentration

Accepted Answer

the concentration of tubulin heterodimers when rate of assembly and disassembly of MTs are the same

Question 25

plus end

Accepted Answer

rapidly growing end with power critical concentrationb-tubulin

Question 26

minus end

Accepted Answer

slower growing end with higher critical concentrationsometimes attached to the centrosome so doesn't polymerize at alla-tubulin

Question 27

treadmilling

Accepted Answer

when the plus end polymerizes while the minutes end depolymerizes

Question 28

antimitotic drugs

Accepted Answer

disrupt the mitotic spindle of dividing cells, blocking the further proves of mitosis

Question 29

colchicine

Accepted Answer

binds to tubulin monomers and inhibits their assembly and fosters the disassembly of existing MTs

Question 30

vinblastine/vincristine

Accepted Answer

cause tubulin to aggregate in cellused in anticancer drugs

Question 31

nocodazole

Accepted Answer

synthetic compound that acts like colchicine but with more easily reversible results

Question 32

taxol

Accepted Answer

binds to microtubules and stabilizes them, causing much of free tubulin to become MTs, this locks cell in mitosisused in breast cancer drugs

Question 33

dynamic instability model

Accepted Answer

microtubules have GTP capwhen tubulin concentration gets low, microtubule catastrophe occurs and GTP cap disappears and microtubules begin to depolymerize. once tubulin concentrations get high, microtubule rescue occurs and microtubule can polymerize again

Question 34

catastrophe

Accepted Answer

more likely at plus endrapid depolymerization of MTs

Question 35

centrioles

Accepted Answer

form basal bodies (MTOC for cilia and flagella)in nonaffiliated cells, centrioles recruit pericentriolar materialwithout centrioles, animal cells can still divide bc chromosomes can organize MTs to some extenthigher plant cells don't need centrioles to have MTOCs

Question 36

rescue

Accepted Answer

the switch from rapid depolymerization to polymerizationoccurs when tubulin concentration is high enough

Question 37

G-TuRC

Accepted Answer

G-tubulin ring complexes formed by G-tubulin and GRiPs (gamma tubulin ring proteins) seen at bases of MTs around centrosomenucleate the assembly of new MTs away from centrosome

Bio Final Lecture 32

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