Bio Final Lecture 32 – Flashcards
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Microtubules are typically _______ in diameter.
25 nm
10-12 nm
25 mm
35 nm
7 nm
answer
25 nm
question
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
answer
dimers, oligomers, protofilaments, sheets of protofilaments, closing of microtubule, elongating microtubule
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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
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cytokinesis of animal cells
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Which stage of microtubule assembly is the stage in which nucleation occurs?
sheets of protofilaments
closing of microtubules
oligomers
dimers
elongation
answer
oligomers
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Tubulin may assemble and disassemble simultaneously in a process known as
dynamic instability.
treadmilling.
microtubule organizing.
MAP motoring.
actin-regulated assembly.
answer
treadmilling.
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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
answer
25 nm; 30 nm
question
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.
answer
are made up of 13 linear protofilaments.
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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
answer
the concentration of tubulin dimers at which assembly is balanced with disassembly.
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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.
answer
describes the alternating cycles of growth and shrinkage in microtubules.
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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
answer
centrosome
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microtubules are composed of
answer
tubulin dimers
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tubulin dimers are
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composed of a-tubulin (minus end) and b-tubulin (plus end)
polymerized from head to tail to form filaments
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microtubules grow
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faster at the plus end then the minus end
from the MTOC
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MTOC
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microtubule organizing center
in plant and animal cells, contains centrosome
has limited number of nucleation and anchorage sites, has most during prophase and prometaphase
where minus end is anchored
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microtubules
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provide stability and are involved in movement, help cell resist compression forces, provide structural framework for organelles
are necessary, without them ER would collapse and golgi would disappear
used in mitosis and meiosis
can 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
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centrosome
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has 2 perpendicular centrioles which are bundles of microtubules
has pericentriolar matrix where microtubules originate from
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cytoplasmic microtubules
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loosely organized, dynamic
visualized with fluorescence microscopy
in animal cells: maintain axons, extend nerve cells, maintain polarized shape of migrating cells from inside the cytoplasm
in plant cells: govern orientation of cellulose microfibrils deposited during growth of cell wall
both: 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
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axonemal microtubules
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highly organized, stable
associated with movement: cilia, flagella, basal bodies where these appendages attach
make up central shaft (axoneme) of cilia and flagella
first to be discovered and studied
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protofilaments
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13 of these are arranged side by side to for MT
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tubulin
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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)
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nucleation
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the aggregation of tubulin dimers into clusters called oligomers which serve as nuclei from which new MTs can grow
significant concentration of tubulin dimers, GTP, and Mg2+ needed to occur
known as lag phase, which takes a long time
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elongation
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the polymerization of microtubules
happens quickly until point when free tubulin becomes limiting
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plateau phase
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when MT assembly and disassembly are balanced
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critical concentration
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the concentration of tubulin heterodimers when rate of assembly and disassembly of MTs are the same
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plus end
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rapidly growing end with power critical concentration
b-tubulin
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minus end
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slower growing end with higher critical concentration
sometimes attached to the centrosome so doesn't polymerize at all
a-tubulin
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treadmilling
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when the plus end polymerizes while the minutes end depolymerizes
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antimitotic drugs
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disrupt the mitotic spindle of dividing cells, blocking the further proves of mitosis
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colchicine
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binds to tubulin monomers and inhibits their assembly and fosters the disassembly of existing MTs
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vinblastine/vincristine
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cause tubulin to aggregate in cell
used in anticancer drugs
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nocodazole
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synthetic compound that acts like colchicine but with more easily reversible results
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taxol
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binds to microtubules and stabilizes them, causing much of free tubulin to become MTs, this locks cell in mitosis
used in breast cancer drugs
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dynamic instability model
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microtubules have GTP cap
when 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
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catastrophe
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more likely at plus end
rapid depolymerization of MTs
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centrioles
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form basal bodies (MTOC for cilia and flagella)
in nonaffiliated cells, centrioles recruit pericentriolar material
without centrioles, animal cells can still divide bc chromosomes can organize MTs to some extent
higher plant cells don't need centrioles to have MTOCs
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rescue
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the switch from rapid depolymerization to polymerization
occurs when tubulin concentration is high enough
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G-TuRC
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G-tubulin ring complexes formed by G-tubulin and GRiPs (gamma tubulin ring proteins)
seen at bases of MTs around centrosome
nucleate the assembly of new MTs away from centrosome
