Lecture 3 - Intermediate Filaments and Microtubules. Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Out of the three types of filaments, which two show the most overlap?

A

Microfilaments and intermediate filaments.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

5 types of IF proteins?

A

Keratins (I are acidic & II are basic), Vimentin (III), Neuronal IF proteins (IV) and Lamins (V).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Keratins (types I and II).

A
  • They are found in the outer epithelia. Prominent in skin, hair and nails.
  • Heterodimers - always found in pairs, one acidic and one basic.
  • Red keratin staining used for their identification.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Vimentin (type III).

A
  • Widely distributed in many different cells.

- Supports cell membranes + keeps organelles correctly positioned.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Neuronal IF proteins (type IV).

A
  • Role in neurotransmission –> they determine the diameter of the axon, which in turn determines the speed of conduction.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Lamins (type V).

A
  • Support the inner nuclear membrane –> determine the structure of the nucleus.
  • Play a role in the organisation of different types of chromatin.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

IF proteins share a general structure. Describe this.

A

They have a globular head and a globular tail (N- and C- termini) with a long alpha helical region inbetween.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How do IF filaments assemble?

A
  1. 2 IF monomers wrap around each other to form parallel dimers.
  2. 2 parallel dimers then go head to tail = antiparallel tetramer.
  3. 2 antiparallel tetramers stack end-on-end = protofilaments.
  4. 2 protofilaments come together to form a protofibril.
  5. 4 protofibrils wrap around each other to form the 10nm IF fibre.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Where is the majority of sequence diversity found between IF proteins?

A

N- and C- termini globular domains. The alpha helical region is highly conserved.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Give an example of a heteropolymer.

A

Keratins - will always be Type I and Type II.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What determines which proteins become homopolymers and which become heteropolymers?

A

Spacer sequences in the alpha helical domain.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

There is one key difference in the formation of IF fibres in comparison to the formation of MTs and MFs. What is this?

A

Does not require ATP/GTP.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Keratins and the epidermis.

A

The skin has several layers of cells. First layer = skin stem cells in the basal epidermal layer. As they differentiate they change keratin expression.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Name two diseases associated with IFs.

A

Bilstering disease - epidermolysis bullosa simplex (EBS).

Hutchinson Gilford Progeria

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Blistering disease - Epidermolysis Bullosa Simplex.

A

Caused by mutations in the N- and C- termini. Protofilaments cannot form. The basal epidermis cannot adhere properly; epidermis and dermis separate easily.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Hutchinson’s Gilford Progeria.

A

Caused by mutations in the LMNA gene. It is a premature ageing disease that produces an abnormal form of Lamin A.

17
Q

Which type of tubulin binds GTP reversibly?

A

Beta tubulin. Can hydrolyse GTP for GDP. Alpha tubulin binds GTP irreversibly.

18
Q

Assembly of MTs?

A
  1. Tubulin dimers come together in a head-to-tail manner; protofilament formation.
  2. Protofilaments come together laterally. Form a sheet that curves to form the 25nm tube.
  3. Have a (+) end and a (-) end. Beta tubulin is found at the (+) end.
  4. If the rate of addition is greater than the rate of hydrolysation then a GTP cap will form.
  5. Assembly is concentration dependent - must be above Cc for addition at both ends (greater at the (+) end).
  6. Once pool is depleted = depolymerisation = greater at the (-) end due to GTP cap.
19
Q

What does MTOC stand for? Where are they located?

A

Microtubule Organising Centre. Just outside the nucleus.

20
Q

Main functions of the MTOC?

A

They direct the organisation of MTs, the movement of vesicles and the orientation of organelles.

21
Q

In animal cells, what is the MTOC called?

A

The centrioles.

22
Q

Cells with flagellar have an additional MTOC. Name this structure and explain its function.

A

Basal body. Organises MTs in the flagellar so they can generate the force for movement.

23
Q

Name the two motor proteins that associate with the MTs for vesicular transport.

A

Kinesins and dyneins (for MFs it is Type I and V myosins).

24
Q

Kinesins and dyneins perform movement in opposite directions. Explain this.

A

Kinesins –> movement AWAY from the MTOC –> Anterograde transport.
Dyneins –> movement towards the MTOC –> Retrograde transport.

25
Q

MTs and MFs are located in different areas of a cell. How can a single cargo access all areas?

A

Carry both kinesin and myosin motors, which can be switched.