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BISC 372 > 1.2 Microtubules and Microtubule Motors > Flashcards

1.2 Microtubules and Microtubule Motors Flashcards

1
Q

What are the functions of microtubules (4)?

A
  1. help determine cell shape
  2. involved in cell motility
  3. intracellular transport of organelles
  4. chromosome separation during mitosis
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2
Q

What structural features do microtubules have (3)?

A
  1. Rigid, hollow structures,. approximately 25nm in diameter
  2. More complex structure than actin filaments
  3. They are dynamic structures
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3
Q

What are the subunits of microtubules?

A

tubulin

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4
Q

Tubulin is a heterodimer of [ ] and [ ], held together by [ ].

A
  1. alpha-tubulin
  2. beta-tubulin
  3. non-covalent bonds
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5
Q

[ ] is bound to each of the two monomers.

A

GTP

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6
Q

GTP bound by alpha-tubulin is [ ] hydrolyzed or exchanged.

A

never

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7
Q

[ ] may be bound to GTP or GDP

A

beta-tubulin

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8
Q

There are six isoforms of [ ] found in mammalian cells, an seven forms of [ ].

A
  1. beta-tubulin
  2. alpha-tubulin
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9
Q

What are the characteristics of protofilament (2)?

A
  1. Each is comprised of alphabeta heterodimers, stacked head to tail
  2. has polarity, with the alpha subunit on the plus end
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10
Q

Each microtubule is made up of [ ] parallel protofilaments.

A

13

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11
Q

Like subunits of adjacent protofilaments make [ ] connections with each other:
* alpha subunits interact with an [ ] of the adjacent protofilament.
* beta subunits interact with a [ ] of the adjacent protofilament.

A
  1. lateral
  2. alpha
  3. beta
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12
Q
  • There is a [ ] contact between like subunits of neighboring protofilaments.
  • The contact results in a [ ] in the microtubule structure.
A
  1. Staggered
  2. helical lattice
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13
Q

Subunits in the microtubule causes microtubule to be very [ ] (actin is much more [ ]).

A
  1. rigid
  2. flexibile
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14
Q

Subunit additions and losses occur almost exclusively at the [ ]:
1. Plus end (beta) [ ] at a greater rate than the minus end (alpha).

A
  1. ends of the filament
  2. grows and shrinks
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15
Q

Microtubule dynamics are similar to actin dynamics, with the exception that it involves specifically [ ].

A

GTP

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16
Q

GTP hydrolysis only occurs within the [ ] subunit.

A

beta-tubulin subunit

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17
Q

When [ ] subunits in the microtubule filament hydrolyze GTP, it is converted into the [ ] of the filament.

A
  1. beta-tubulin
  2. D-form
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18
Q

When T form converts to D form, the [ ] free energy change of GTP hydrolysis shifts:
* the tubulin subunits in the D form have a more [ ] free energy change of dissociation than those in the T form.
* this means that the dissociation of subunits in the [ ] form is more favorable that those in the [ ] form

A
  1. negative free energy change
  2. negative
  3. D form
  4. T form
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19
Q

The critical concentraton of the [ ] form is greater than the Cc of the [ ] form.

A
  • D form
  • T form
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20
Q

Under physiological conditions, D form tends to [ ], while T form [ ]

A
  1. depolymerizes
  2. polymerizes
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21
Q

What is dynamic instability?

A

rapid conversion between the growing and shrinking states at a uniform tubulin concentration

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22
Q

What is catastrophe?

A

growing into shrinking

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23
Q

What is rescue?

A

shrinking into growing

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24
Q

Why does ATP hydrolysis in actin filaments cause treadmilling, but dynamic instability in microtubules?

A

tubulin subunits have relatively low affinity for each other, with a very high koff/kon

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25
When GTP is hydrolyzed at the filament end, it is quicker to [ ].
depolymerize
26
Nucleation in intracellular location is known as the [ ].
microtubule-organizing center (MTOC)
27
Spontaneous nucleation requires high concentration of [ ] and help from other factors such as [ ].
1. tubulin subunits 2. gamma-Tubulin
28
Nucleation often depends on [ ].
gamme-tubulin ring complex (gamma-TuRC)
29
[ ] bind to gamma-tubulin.
Two accessory proteins
30
[ ] of gamma-tubulin molcules forms with help of other proteins.
spiral ring
31
What is a centrosome?
the name of a single, well-defined MTOC found in many animal cells, next to the nucleus. Located adjacent to the nucleus
32
Each centrosome recruits [ ] gamma-TuRC.
50
33
Microtubules are nuclueated at their [ ] ends, to allow for growth/shrinkage from their [ ] ends, extending out into [ ].
1. minus ends 2. plus ends 3. three-dimensions
34
Centrosome is [ ] essential for nucleation. Many gamma-TuRC are found in the [ ].
1. not 2. cytoplasm
35
Cytoplasmic arrangement of microtubules vary by [ ].
cell type
36
Yeasts nucleate at a small MTOC called [ ] embedded in nuclear envelope.
spindle pole body
37
[ ] lack centrosomes and nucleate all over [ ] and [ ] (underlies plasma membrane).
1. higher plants 2. nuclear envelope 3. cell cortex
38
[ ] and [ ] of neurons, for example, need microtubules to create their structures.
1. axons 2. dendrites
39
What are microtubule-associated proteins (MAPs)?
a collective term that refers to proteins that bind to microtubules
40
What are the functions of MAPs (2)?
1. can stabilize microtibules to help prevent disassembly 2. some mediate the connection of microtubules to cell structures
41
MAPs typically bind to microtubules through [ ] interactions. * alpha-tubulin and beta-tubulin have [ ] rich with [ ] and [ ] acid residues and give the surface of microtubules are a net [ ] charge. * many MAPs have a net [ ] charge.
1. electrostatic 2. C-terminal tails 3. aspartic 4. glutamic 5. negative 6. positive
42
Activity and localization of MAPs can be regulated through [ ]. [ ] disrupts electrostatic interactions.
1. kinase activity 2. phosphorylation
43
MAPS can recruit other proteins to aid in [ ] of the microtubule cytoskeleton.
organization
44
What is augmin?
a protein that binds to microtubules and recruits gamma-TuRC. This nucleates a new microtubule from a branch point
45
What are the MAPs and microtubule dynamics (3)?
1. plus end-binding proteins 2. tubulin sequestering proteins 3. microtubule severing proteins
46
[ ] ends are usually stabilized and inert. [ ] end is dynamic.
1. minus ends 2. plus ends
47
Many proteins bind to the plus end and influence dynamics. Collectively called [ ].
plus end-binding proteins
48
What is the function of plus end-binding proteins?
influence the rate of catastrophes or rescues
49
What is the function of kinesin-13?
bind to ends of filaments and pry them apart. This lowers the threshold for transition to catastrophe, promoting the shrinking stage
50
What is the function of XMAP215?
a protein that facilitates growth. Does this by delivering subunits to the plus end.
51
The cell sequesters [ ]. This is to maintain [ ].
1. unpolymerized tubulin subunits 2. a level of available subunits near the Cc.
52
What is the function of stathmin?
binds to two tubulin heterodimers, making them unavailable for polymerization
53
Stathmin activity can be inhibited via [ ].
phosphorylation
54
What is severing?
a mechanism used to destabilize microtubules
55
Severing proteins must break the longitudinal bond across [ ] protofilaments.
all 13
56
What is the function of Katanin?
uses ATP hydrolysis to extract tubulin subunits from the microtubule wall. This leads to destabilization and breakage. Also releases microtubules from MTOCs
57
How do severing proteins play a role in microtubule stabilization?
extracted subunits are likely to be GDP-bound. New GTP bound subunits can replace those that were extracted
58
If replacement of extracted subunits with GTP-bound heterodimers occurs [ ] severing is complete, a new stable [ ] end is available for growth
1. before 2. plus end
59
What are the major classes of motor proteins (2)?
1. kinesins 2. dyneins
60
What are the major functions of motor proteins (3)?
1. move organelles and macromolecules within the cell 2. slide microtubules relative to one another. Used to generate specific arrangements 3. regulate microtubule dynamics
61
What are kinesins?
large group of proteins with a motor domain at the N-terminus of the heavy chain
62
Most kinesins contain two [ ] that dimerize through a coiled coil.
heavy chains
63
Kinesins "walk" towards the [ ] of the filament.
plus end
64
Kinesins with a [ ] at the C-terminus "walk" towards the minus end of the filament.
motor domain
65
[ ] has a central motor domain, and doesn't walk at all.
Kinesin-13
66
Some kinesins may be [ ] or [ ].
monomers or tetramers
67
Some kinesin motors may use a [ ] or [ ] to link a membrane-enclosed organelle.
1. light chain 2. adaptor protein
68
Some kinesins use a [ ] to facilitate crosslinking/sliding of two microtubules.
second microtubule binding domain
69
What are Dyneins?
a family of minus-end directed microtubule motors.
70
Dyneins are composed of either [ ] heavy chains, each including a [ ].
1. one, two, or three 2. motor domain
71
Heavy chains are associated with a variable number of [ ].
light chains, light-intermediate chains, or intermediate chains
72
As for myosin and kinesins, dyneins couple [ ] to filament binding, unbinding, and conformational change.
ATP hydrolysis
73
Cilia and flagella are composed of [ ].
microtubules and dyneins
74
Flagella allow for cells to [ ] through a liquid environment.
swim
75
Cilia produce [ ] motion. The beating can propel [ ], or can be used to move [ ].
1. whip-like 2. a single cell through a medium 3. fluid over the surface of a group of cells
76
Both microtubule-polymerizing and microtubule-depolymerizing drugs preferntially [ ].
kill dividing cells
77
Mitotic spindle function is dependent on properly functioning [ ].
microtubule dynamics
78
What is taxol?
a microtubule-polymerizing drug that is sometimes used to treat breast and lung cancers

BISC 372 (7 decks)

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