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Molecules to Cells - Biochemistry > Lecture 4. The Cytoskeleton II - Tubulin > Flashcards

Lecture 4. The Cytoskeleton II - Tubulin Flashcards

1
Q

What are microtubules ?

A

A network of filaments that generally extend from the centrosome, near the centre of the cell out to the periphery of the cytoplasm

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2
Q

What are the role of microtubules ?

A

To organise the cytoplasm

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3
Q

What are microtubules made up of ?

A

Repeating units of tubulin dimers.

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4
Q

What is a dimer ?

A

Composed of alpha and beta tubulin which form a non-covalently bound protofilament structure

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5
Q

Do protofilaments have structural polarity ?

A

Yes

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6
Q

Explain protofilaments structural polarity ?

A

The beta tubulin is exposed at the plus end and the alpha tubulin is exposed at the minus end

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7
Q

How many protofilaments stack against each other to form a lumen

A

13 parallel protofilaments

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8
Q

Are microtubules more rigid and straighter than actin filaments ?

A

Yes

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9
Q

How does microtubule nucleation occur ?

A

Via the gamma tubulin ring complex (Y TuRC)

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10
Q

Where does microtubule nucleation occur ?

A

At the microtubule organising centre (MTOC)

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11
Q

Does the nucleation step of polymerisation occur spontaneously ?

A

No

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12
Q

Why does the nucleation step of polymerisation not occur spontaneously ?

A

It involves the association of 13 protofilaments

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13
Q

What is the gamma tubulin ring composed of ?

A

Gamma tubulin

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14
Q

What does the gamma tubulin ring serve as ?

A

An initiation or nucleation site

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15
Q

What is the function of the tubulin dimers in microtubule nucleation ?

A

They associate with the gamma tubulin ring complex in a specific orientation, which results in the minus end of the microtubule being bound to this gamma tubulin ring complex, with the plus end growing outwards into the cell

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16
Q

What is the centrosome ?

A

The microtubule organising centre (MTOC) located near the centre of the animal cell

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17
Q

What is the centrosome composed of ?

A

A pair of centrioles surrounded by a fibrous matrix and contains up to hundreds of gamma tubulin ring complexes on its surface.

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18
Q

What is the function of the hundreds of gamma tubulin ring complexes on the surface of the centrosome ?

A

To allow the growth of hundreds of microtubules from the centrosome structure.

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19
Q

What is the function of the microtubules extending out to the cell periphery ?

A

Creates a series of tracks upon which organelles, vesicles and other cell components can be transported

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20
Q

What is dynamic instability ?

A

The distinctive growth pattern microtubules display after they have been nucleated

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21
Q

What does the term catastrophe mean ?

A

Rapid shrinkage phase

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22
Q

What is the distinctive growth pattern ?

A

A repeated sequence of rapid microtubule growth out from the centrosome followed by a rapid shrinkage phase

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23
Q

What is responsible for the distinctive growth pattern ?

A

The hydrolysis of GTP bound tubulin

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24
Q

Where initially is GTP bound tubulin incorporated ?

A

Into the growing microtubule

25
Q

When is the GTP tubulin hydrolysed and by what ?

A

GTP tubulin is hydrolysed by GDP tubulin shortly after its incorporation into the microtubule.

26
Q

What does the GDP bound tubulin have less of an affinity for ?

A

The other tubulin dimers inside the microtubule

27
Q

How is the GTP cap formed ?

A

When polymerisation is rapidly proceeding the GTP bound tubulin dimers are being incorporated into the microtubule at a faster rate than that of the hydrolysis of GTP to GDP forming a GTP cap

28
Q

What happens when the rate of microtubule growth slows to below the rate of GTP hydrolysis ?

A

The GTP tubulin subunits within the GTP cap will be hydrolysed to GDP tubulin, which dissociates from the microtubule.

29
Q

Why does depolymerisation continue at a catastrophic rate ?

A

The GTP cap is hydrolysed to GDP tubulin and the rest of the microtubule is composed of GDP tubulin

30
Q

What happens when GDP tubulin dimers are released from the microtubule into the cytosol ?

A

They exchange their bound GDP for GTP favouring the rescue phase and the reformation of the GTP cap

31
Q

What is dynamic instability the main pathway of ?

A

Microtubule turnover in cells

32
Q

What is an advantage of dynamic instability ?

A

The microtubules are very adaptable cytoskeletal filaments that can rapidly reorganise to different locations within the cell

33
Q

What does GTP hydrolysis do ?

A

Controls the growth of microtubules

34
Q

The dynamic properties of microtubules are essential for what functions ?

A

Allowing them to search intracellular space and quickly find their targets, regardless of location

35
Q

What can the growing or shrinking of microtubules generate ?

A

They can generate force and be used to move vesicles and other subcellular organelles around the cell

36
Q

What does the EB1 protein do ?

A

Binds to the GTP tubulin cap at the growing ends of the microtubules

37
Q

What is the function of microtubules during mitosis ?

A

Form spindle

38
Q

What do differentiated cells do to microtubules ?

A

They suppress microtubule dynamic instability

39
Q

How are microtubule dynamic instability suppressed in differentiated cells ?

A

They use microtubule binding proteins to stabilise filaments.

40
Q

What is the function of stabilised filaments in differentiated cells ?

A

Maintain organisation of cell

41
Q

How do microtubules form spindle during mitosis ?

A

Microtubules become more dynamic enabling them to disassemble rapidly and reassemble into mitotic spindle

42
Q

What organises the interior of the cell ?

A

Microtubules and their motor protein

43
Q

What facilitates the transport of proteins, organelles and vesicles along microtubules ?

A

Specialised microtubule binding motor proteins

44
Q

How do specialised microtubule binding proteins travel and carry their cargo ?

A

They use energy from ATP hydrolysis

45
Q

What are the two motor protein families that move along the cytoplasmic microtubules ?

A
  1. Kinesins

2. Dyneins

46
Q

What are kinesins ?

A

These move towards the plus end of the microtubule and away from the centrosome. Carry binding site in tail region

47
Q

What are dyneins ?

A

Move towards the minus end or towards the centrosome

48
Q

What are the two types of dyneins and their functions ?

A
  1. Cytoplasmic dyneins - vesicle trafficking and golgi localisation.
  2. Axonemal dyneins/cilliary dyneins - sliding movements of microtubules that drive ciliary and flagella beating
49
Q

What are kinesins structurally similar to ?

A

Myosin

50
Q

What do kinesins have roles in ?

A

Cell division

51
Q

What are flagella and cilia built from ?

A

Axonemal dyneins and microtubules

52
Q

Where are flagella found ?

A

Sperm and many protozoa

53
Q

What enables flagella movement ?

A

The wavelike motion

54
Q

Where would you find cilia

A

They line the respiratory tract and the oviduct

55
Q

What type of motion do cilia have ?

A

Whiplike motion

56
Q

What happens in isolated doublet microtubules ?

A

Dynein produced microtubule sliding

57
Q

In normal flagellum what causes microtubule bending ?

A

Dynein

58
Q

What are basal bodies ?

A

They are the root of cilia and flagella. Modified centriole

59
Q

What are basal bodies composed of ?

A

9 fused triplet microtubules in a cartwheel

Molecules to Cells - Biochemistry (17 decks)

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