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BIO130 > Week 10 - The Cytoskeleton and Microtubules > Flashcards

Week 10 - The Cytoskeleton and Microtubules Flashcards

1
Q

What are the 5 functions of the cytoskeleton?

A
  1. Provides structural support
  2. Positions organelles
  3. Directs vesicular transport
  4. Involved in locomotion
  5. Required for cell division
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2
Q

What are the 4 main structures of the cytoskeleton?

A
  1. Actin filaments
  2. Intermediate filaments
  3. Microtubules
  4. Motor proteins
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3
Q

What are the 3 types of filaments that form the cytoskeleton?

A
  1. Microfilaments (actin filaments)
  2. Intermediate filaments (intermediate filament proteins)
  3. Microtubules (Tubulin)
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4
Q

What is immunofluorescence and what is it used for?

A

It is a technique used to determine the location of proteins within the cell, not just the cytoskeleton.

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5
Q

How is immunofluorescence done?

A
  1. Antibody is used which binds to the protein of interest
  2. A second antibody binds to the first and is covalently tagged with a fluorescent molecule
  3. A fluorescence microscope is used to excite the fluorescent molecule and visualize the light emitted.
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6
Q

Why does the light microscope have a resolution limit?

A

Due to diffraction; it is based on the wavelength of light.

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7
Q

Why does the electron microscope have a higher resolution than the light microscope?

A

It uses electrons, which have a shorter wavelength than light; can therefore see clearer.

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8
Q

For cell motility and crawling, what must the actin filaments rapidly do?

A

They must rapidly disassemble and reassemble at the leading edge.

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9
Q

Most interphase microtubules radiate from what?

A

They radiate from one microtubule organizing centre.

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10
Q

What are microtubules reorganized to form in dividing cells?

A

Bipolar mitotic spindles.

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11
Q

A microtubule is made up of what?

A

13 protofilaments of tubulin in a hollow cylinder formation.

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12
Q

Microtubules are involved in what 5 things?

A
  1. Intracellular transport
  2. Structural support
  3. Cell organization
  4. Mitosis (mitotic spindle)
  5. Cell motility (flagella and cilia)
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13
Q

Microtubules are inextensible. Does this mean they don’t extend?

A

No, microtubules do grow and shrink. Inextensible means that they are not elastic.

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14
Q

Microtubules are made up of individual subunits of what 2 things?

A
  1. Alpha-tubulin

2. Beta-tubulin

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15
Q

Together, Alpha-tubulin, Beta-tubulin, and GTP form what?

A

A tubulin heterodimer.

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16
Q

Tubulin heterodimers bind together to form what?

A

Form a protofilament.

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17
Q

The regular arrangement of alpha and beta subunits give the microtubule what?

A

Polarity; Beta is a plus end and alpha is a minus end.

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18
Q

What is at the minus end of a microtubule?

A

An alpha-tubulin subunit.

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19
Q

What is at the plus end of a microtubule?

A

A beta-tubulin subunit.

20
Q

What happens to GTP is a heterodimer has been attached to a microtubule for a while?

A

GTP is cut to GDP; usually by the Beta-tubulin.

21
Q

How do GTP caps form on microtubules?

A

GTP caps form as new heterodimers (with uncut GTP) add onto the plus end (beta-tubulin).

22
Q

How is the plus end of a microtubule stabilized as to not lose heterodimers?

A

The minus end is stabilized by microtubule organizing centres (MTOCs).

23
Q

Where does all loss and addition occur on a microtubule?

A

At the plus end.

24
Q

What is an MTOC and what is it’s function?

A

Microtubule organizing centre; structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions:

  1. the organization of eukaryotic flagella and cilia
  2. the organization of the mitotic and meiotic spindle apparatus.
25
Q

What does an MTOC consist of?

A

Made up of a pair of centrioles at its centre, and is surrounded by pericentriolar material (PCM).

26
Q

What kind of bonds are between individual subunits of a protofilament?

A

All bonds are non-covalent.

27
Q

Where are the non-covalent bonds the strongest in a microtubule?

A

Within the heterodimers.

28
Q

A heterodimer just added to the end of a protofilament while be what form?

A

It will be t-form (microtubule t-form cap), as GTP has yet to be cut to GDP.

29
Q

In vitro microtubule growth is faster at which end?

A

At the plus (beta-tubulin) end.

30
Q

What form of free heterodimers are bound to GTP?

A

The T-form of heterodimers.

31
Q

What do tubulin subunits (as enzymes) hydrolyze?

A

Hydrolyze Guanosine triphosphate (GTP).

32
Q

How do D-form heterodimers occur?

A

After GTP is hydrolyzed, GDP gets trapped in the tubulin subunits and forms D-form heterodimers.

33
Q

The microtubule GTP cap stabilizes which end?

A

The plus end.

34
Q

What form of heterodimers make up the stabilizing cap?

A

T-form heterodimers (with GTP).

35
Q

Why does the GTP cap stabilize at the plus end?

A
  1. The plus end favours microtubule growth

2. dimers in t-form bind more strongly to other dimers in the tubule

36
Q

What does hydrolysis of bound GTP reduce in the subunits?

A

It reduces binding affinity.

37
Q

What is dynamic instability?

A

Dynamic instability is the stoppage of addition of new heterodimers to a microtubule; tubule closure, leads to catastrophe.

38
Q

What happens when both ends of a microtubule had hydrolyzed, d-form heterodimers?

A

The tubule is closed, and it leads to catastrophe as heterodimers start to subtract.

39
Q

Where are microtubules nucleated?

A

At the MTOC.

40
Q

The centrosome is an example of what?

A

A MTOC; nucleates the formation of microtubules.

41
Q

Plus ends of microtubules radiate where?

A

Radiate out towards the plasma membrane (PM).

42
Q

Microtubules are joined to MTOC’s at which end?

A

At their minus ends.

43
Q

What do gamma (y) tubulin do at the MTOC?

A

They are on the centrosome for stabilizing.

44
Q

What is a gamma-TuRC? (y-TuRC)

A

A complex of proteins that form a ring structure.

45
Q

How does gamma-TuRC bind to tubulin subunits?

A

y-tubulin binds the ring structure of y-TuRC to act as an attachment site for a/B-tubulin dimers.

46
Q

What do y-tubulin and y-TuRC form?

A

They form a stabilizing cap at the microtubule minus (alpha) end.

BIO130 (12 decks)

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