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BIO130 > Week 10 - Filament Formation and Motor Proteins > Flashcards

Week 10 - Filament Formation and Motor Proteins Flashcards

1
Q

What is Kinesin and what does it do?

A

A motor protein that walks along microtubules to carry vesicles.

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2
Q

What are the 2 types of Axonal Vesicular Transport?

A
  1. Dynein movement

2. Kinesin movement

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3
Q

What direction does Kinesin move in?

A

Moves towards the axon terminus/ microtubule PLUS end (Beta-tubulin).

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4
Q

What direction does Dynein move in?

A

Moves towards the cell body/microtubule MINUS end (alpha-tubulin).

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5
Q

How are some organelles transported?

A

Via microtubule walking of motor proteins.

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6
Q

What organelle is closer to the PLUS end of the microtubule?

A

The endoplasmic reticulum.

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7
Q

What organelle is closer to the MINUS end of the microtubule?

A

The Golgi apparatus.

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8
Q

Which motor protein walks from the Golgi apparatus to the ER?

A

Kinesin; walks towards PLUS end.

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9
Q

Which motor protein walks from the ER to the Golgi apparatus?

A

Dynein; walks towards MINUS end.

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10
Q

The Golgi apparatus is different from the centrosome, but still an example of what?

A

Example of a MTOC.

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11
Q

What 3 things are microfilaments/actin filaments involved in?

A
  1. Cell motility (crawling)
  2. Contractile activity
  3. Cytokinesis
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12
Q

What are actin filaments made of?

A

Actin monomers; helical filaments (2 protofilaments twisted in a helix)

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13
Q

What motor protein acts on actin filaments?

A

Myosin.

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14
Q

Are actin filaments polar?

A

Yes; due to the regular orientation of actin monomers in each protofilament.

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15
Q

Free actin monomers are bound to what?

A

Bound to ATP; at the centre of the protein.

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16
Q

Actin is an ATPase that hydrolyzes what?

A

Hydrolyzes ATP; ADP remains bound

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17
Q

Growth of actin filaments is faster at which end?

A

Faster at the plus end.

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18
Q

Actin filaments have what kind of cap?

A

An ATP cap.

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19
Q

Actin filaments are polar; what is at both ends?

A

One end has N and C terminus, the other end doesn’t.

20
Q

What is at the plus end of an actin filament?

A

The plus end of an actin monomer has an N and C termini.

21
Q

What is at the minus end of an actin filament?

A

No terminus.

22
Q

What happens when all actin monomers are d-form at the cap?

A

Disassembly of the monomer occurs when all ATP is hydrolyzed to ADP.

23
Q

Differences in Microtubules and Actin Filaments?

A

Microtubules Actin-
Filaments

-heterodimers -monomers
-GTP or GDP -ATP or ADP
-GTP cap -ATP cap
-T and D-form -T and D-form
heterodimers monomers
-13 parallel -2 protofilaments protofilaments twisted
forming hollow around each
cylinder other -dynein/kinesin -myosin

24
Q

3 steps of actin polymerization in vitro?

A
  1. Nucleation (everything monomers)
  2. Elongation (growth phase)
  3. Steady state (equilibrium phase)
25
Q

What is the Critical concentration during actin polymerization in vitro?

A

CC: Critical concentration

  • not everything in the filament
  • to keep this requires a continual supply of actin bound to ATP
  • monomers coming on/off (filament doesn’t change in length)
26
Q

Which end of actin filaments has a higher affinity for actin monomers?

A

The plus end.

27
Q

Although actin filaments look stable, there is a constant exchange of what?

A

There is a constant exchange of monomers art the ends.

28
Q

What is actin filament tread-milling?

A

As there is a constant exchange of actin monomers, a pulse of labelled actin monomers will “move down” or “treadmill” an actin filament; until all monomers are eventually replaced.

29
Q

What proteins are involved in actin filament assembly?

A
  1. Profilin: inhibits nucleation, speeds elongation

2. Cofilin; accelerated disassembly.

30
Q

What is the structure of Myosin?

A
  • 2 heavy and 4 light chains
  • tails of the 2 heavy chains are organized in a coiled-coil
  • 2 heads associated with 2 light chains each (4 total)
  • ATP hydrolyzed at myosin head.
31
Q

Which Myosin activity on actin filaments causes muscles to contract?

A

Mysoin II motor activity.

32
Q

When a muscle contracts, what is Myosin II doing?

A

Myosin II shortens and pulls actin filaments closer together (stretches them) to contract muscle fibres.

33
Q

What are common mechanisms of all motor proteins?

A
  • they all couple ATP hydrolysis with conformational changes to generate force
  • all move in a specific direction along filaments with polarity.
34
Q

What do Intermediate Filaments provide?

A

Structural support.

35
Q

Intermediate filaments have 3 propeties…

A
  1. Tough
  2. Flexible
  3. Extensible; unlike actin and microtubules, they ARE elastic!
36
Q

Intermediate filament are not found where?

A
  • NOT in plant cells

- not in ALL animal cells

37
Q

Intermediate filaments are prominent in what kind of cells?

A

Cells subjected to mechanicla stress; i.e. epithelial calls (keratin), neurons (neurofilament proteins), muscle cells (desmin).

38
Q

What is the structure of an Intermediate Filament?

A

A coiled-coild dimer forms a STAGGERED antiparallel tetramer.

39
Q

Are intermediate proteins polar?

A

NO; there is no filament polarity. Despite it’s monomer starting with polarity, after dimers form and come together to form a tetramer, polarity is lost.

40
Q

Do intermediate filaments have motor proteins?

A

No; motor proteins require polarity.

41
Q

Intermediate filaments pack together into what structure?

A

Pack into rope-like filaments.

42
Q

Where are Keratin Filaments anchored in epithelial cells?

A

Anchored at the sites of cell to cell contact by desmosomes; held by mechanical strength.

43
Q

Keratin filaments from neighbouring cells anchor at the cell boundary but do not do what?

A

They anchor at the cell boundary but DO NOT cross boundaries.

44
Q

Keratin filaments can also anchor to what?

A

Can also anchor to hemi-desmosomes.

45
Q

Where are hemi-desmosomes anchored?

A

Anchored to the extracellular matrix (ECM).

BIO130 (12 decks)

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