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BC3003: Introduction to Cell Biology & Biomembranes > Microtubules > Flashcards

Microtubules Flashcards

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1
Q

What are Microtubules?

A

Polymers of Tubulin

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2
Q

What is Tubulin?

A

A dimer of two subunits, α and β tubulin

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3
Q

What energy source do α and β tubulin bind?

A

GTP

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4
Q

Which form of Tubulin is GTP hydrolysed in?

A

β tubulin

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5
Q

What is the diameter of Microtubules?

A

25nm

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6
Q

What are Microtubules formed from?

A

13 protofilaments

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7
Q

What do Microtubule protofilaments consist of?

A

Tubulin dimers aligned end-to-end

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8
Q

What is the polarity of Protofilaments in a Microtubule in regards to Tubulin?

A
  • α-tubulin at (-) end
  • β-tubulin at (+) end
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9
Q

TRUE OR FALSE:
Critical concentration for addition of αβ tubulin dimers is the same for both ends of the microtubule?

A

False.
Critical concentration is DIFFERENT for both ends

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10
Q

TRUE OR FALSE:
At steady state, there is net ADDITION of tubulin at the (+) end and net LOSS at the (-) of the Microtubule?

A

True

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11
Q

What is Dynamic Instability in Microtubules?

A

Switching of the (+) end between growing and shrinking states

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12
Q

Where are DOUBLET microtubules found?

A
  • Cilia
  • Flagella
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13
Q

Where are TRIPLET microtubules found?

A
  • Basal bodies
  • Centrioles
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14
Q

How are Microtubules nucleated?

A

By structures called Microtubule-Organising Centres (MTOCs)

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15
Q

What is the MTOC of Interphase cells?

A

Centrosome

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16
Q

What is a Centrosome?

A

A pair of centrioles arranged orthogonally surrounded by the pericentriolar material

17
Q

What is a Centriole?

A

A cylinder composed of nine sets of triplet microtubules

18
Q

What is the function of Microtubule Associated Proteins (MAPs)?

A

Stabilise and organise and destabilise microtubules

19
Q

Where do Microtubule Associated Proteins (MAPs) bind?

A

Bind to sides and ends of microtubules

20
Q

What are TWO examples of Microtubule Associated Proteins (MAPs)?

A

Tau & MAP2

21
Q

Where is MAP2 found?

A

Only in dendrites

22
Q

Where is Tau found?

A

In axons (and dendrites)

23
Q

How is microtubule binding of Tau regulated?

A

Phosphorylation

24
Q

What does hyperphosphorylation of Tau cause?

A

Pathogenic role in Alzheimer’s disease

25
Q

What is the function of Microtubules in cells?

A

Intracellular transport system
* motor proteins carrying cargo move along them

26
Q

Which end of Microtubules do Kinesins move towards?

A

Towards the (+) end

27
Q

Which end of Microtubules do Dyneins move towards?

A

Towards the (-) end

28
Q

What is the molecular weight of Kinesin?

A

380 kDa

29
Q

What is the structure of Kinesin?

A
  • Dimeric
  • Motor domains (which binds microtubules)
  • Long “stalk” and a “tail”
30
Q

What is an example of Microtubule-based transport?

A

Vesicular and Organelle Transport
* aggregation and dispersion of pigement granules in skin cells

31
Q

What is the orientation of microtubules in axons?

A

Unipolar

32
Q

Which motor protein is involved in Anterograde transport in axonal transport?

A

Kinesin

33
Q

Which motor protein is involved in Retrograde transport in axonal transport?

A

Dynein

34
Q

Where do Cilia and Flagella arise from?

A

Arise from a basal body Microtubule Organising Centres (MTOCs)

35
Q

Which motor protein is involved in the movement of motile Cilia and Flagella?

A

Dyneins

36
Q

Which motor proteins are required for the formation and maintenance of Cilia and Flagella?

A

Kinesins

37
Q

Where are Kinetochores located during Mitosis?

A

At the centromere of the chromosome centromere

38
Q

What is the function of Kinetochores in Mitosis?

A

“Capture” and stabilise microtubules

BC3003: Introduction to Cell Biology & Biomembranes (15 decks)

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