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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
Q

When GTP is hydrolyzed at the filament end, it is quicker to [ ].

A

depolymerize

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26
Q

Nucleation in intracellular location is known as the [ ].

A

microtubule-organizing center (MTOC)

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27
Q

Spontaneous nucleation requires high concentration of [ ] and help from other factors such as [ ].

A
  1. tubulin subunits
  2. gamma-Tubulin
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28
Q

Nucleation often depends on [ ].

A

gamme-tubulin ring complex (gamma-TuRC)

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29
Q

[ ] bind to gamma-tubulin.

A

Two accessory proteins

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30
Q

[ ] of gamma-tubulin molcules forms with help of other proteins.

A

spiral ring

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31
Q

What is a centrosome?

A

the name of a single, well-defined MTOC found in many animal cells, next to the nucleus. Located adjacent to the nucleus

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32
Q

Each centrosome recruits [ ] gamma-TuRC.

33
Q

Microtubules are nuclueated at their [ ] ends, to allow for growth/shrinkage from their [ ] ends, extending out into [ ].

A
  1. minus ends
  2. plus ends
  3. three-dimensions
34
Q

Centrosome is [ ] essential for nucleation. Many gamma-TuRC are found in the [ ].

A
  1. not
  2. cytoplasm
35
Q

Cytoplasmic arrangement of microtubules vary by [ ].

36
Q

Yeasts nucleate at a small MTOC called [ ] embedded in nuclear envelope.

A

spindle pole body

37
Q

[ ] lack centrosomes and nucleate all over [ ] and [ ] (underlies plasma membrane).

A
  1. higher plants
  2. nuclear envelope
  3. cell cortex
38
Q

[ ] and [ ] of neurons, for example, need microtubules to create their structures.

A
  1. axons
  2. dendrites
39
Q

What are microtubule-associated proteins (MAPs)?

A

a collective term that refers to proteins that bind to microtubules

40
Q

What are the functions of MAPs (2)?

A
  1. can stabilize microtibules to help prevent disassembly
  2. some mediate the connection of microtubules to cell structures
41
Q

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.

A
  1. electrostatic
  2. C-terminal tails
  3. aspartic
  4. glutamic
  5. negative
  6. positive
42
Q

Activity and localization of MAPs can be regulated through [ ]. [ ] disrupts electrostatic interactions.

A
  1. kinase activity
  2. phosphorylation
43
Q

MAPS can recruit other proteins to aid in [ ] of the microtubule cytoskeleton.

A

organization

44
Q

What is augmin?

A

a protein that binds to microtubules and recruits gamma-TuRC. This nucleates a new microtubule from a branch point

45
Q

What are the MAPs and microtubule dynamics (3)?

A
  1. plus end-binding proteins
  2. tubulin sequestering proteins
  3. microtubule severing proteins
46
Q

[ ] ends are usually stabilized and inert. [ ] end is dynamic.

A
  1. minus ends
  2. plus ends
47
Q

Many proteins bind to the plus end and influence dynamics. Collectively called [ ].

A

plus end-binding proteins

48
Q

What is the function of plus end-binding proteins?

A

influence the rate of catastrophes or rescues

49
Q

What is the function of kinesin-13?

A

bind to ends of filaments and pry them apart. This lowers the threshold for transition to catastrophe, promoting the shrinking stage

50
Q

What is the function of XMAP215?

A

a protein that facilitates growth. Does this by delivering subunits to the plus end.

51
Q

The cell sequesters [ ]. This is to maintain [ ].

A
  1. unpolymerized tubulin subunits
  2. a level of available subunits near the Cc.
52
Q

What is the function of stathmin?

A

binds to two tubulin heterodimers, making them unavailable for polymerization

53
Q

Stathmin activity can be inhibited via [ ].

A

phosphorylation

54
Q

What is severing?

A

a mechanism used to destabilize microtubules

55
Q

Severing proteins must break the longitudinal bond across [ ] protofilaments.

56
Q

What is the function of Katanin?

A

uses ATP hydrolysis to extract tubulin subunits from the microtubule wall. This leads to destabilization and breakage. Also releases microtubules from MTOCs

57
Q

How do severing proteins play a role in microtubule stabilization?

A

extracted subunits are likely to be GDP-bound. New GTP bound subunits can replace those that were extracted

58
Q

If replacement of extracted subunits with GTP-bound heterodimers occurs [ ] severing is complete, a new stable [ ] end is available for growth

A
  1. before
  2. plus end
59
Q

What are the major classes of motor proteins (2)?

A
  1. kinesins
  2. dyneins
60
Q

What are the major functions of motor proteins (3)?

A
  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
Q

What are kinesins?

A

large group of proteins with a motor domain at the N-terminus of the heavy chain

62
Q

Most kinesins contain two [ ] that dimerize through a coiled coil.

A

heavy chains

63
Q

Kinesins “walk” towards the [ ] of the filament.

64
Q

Kinesins with a [ ] at the C-terminus “walk” towards the minus end of the filament.

A

motor domain

65
Q

[ ] has a central motor domain, and doesn’t walk at all.

A

Kinesin-13

66
Q

Some kinesins may be [ ] or [ ].

A

monomers or tetramers

67
Q

Some kinesin motors may use a [ ] or [ ] to link a membrane-enclosed organelle.

A
  1. light chain
  2. adaptor protein
68
Q

Some kinesins use a [ ] to facilitate crosslinking/sliding of two microtubules.

A

second microtubule binding domain

69
Q

What are Dyneins?

A

a family of minus-end directed microtubule motors.

70
Q

Dyneins are composed of either [ ] heavy chains, each including a [ ].

A
  1. one, two, or three
  2. motor domain
71
Q

Heavy chains are associated with a variable number of [ ].

A

light chains, light-intermediate chains, or intermediate chains

72
Q

As for myosin and kinesins, dyneins couple [ ] to filament binding, unbinding, and conformational change.

A

ATP hydrolysis

73
Q

Cilia and flagella are composed of [ ].

A

microtubules and dyneins

74
Q

Flagella allow for cells to [ ] through a liquid environment.

75
Q

Cilia produce [ ] motion. The beating can propel [ ], or can be used to move [ ].

A
  1. whip-like
  2. a single cell through a medium
  3. fluid over the surface of a group of cells
76
Q

Both microtubule-polymerizing and microtubule-depolymerizing drugs preferntially [ ].

A

kill dividing cells

77
Q

Mitotic spindle function is dependent on properly functioning [ ].

A

microtubule dynamics

78
Q

What is taxol?

A

a microtubule-polymerizing drug that is sometimes used to treat breast and lung cancers

BISC 372 (7 decks)

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