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211: Cell Biology > 2. The Cytoskeleton > Flashcards

2. The Cytoskeleton Flashcards

1
Q

what is the basic component of microfilaments

A

actin

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2
Q

what comprises actin

A

G-actin assembles into F-actin (reversible process)

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3
Q

where does ATP bind on actin

A

at the (-) end

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4
Q

true or false:

actin is polarised

A

true

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5
Q

ATP binds to actin extending the chain, what’s the formula:

A

G-actin + ATP -> ADP-f-actin

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6
Q

where does growth occur on the actin chain

A

at the (+) end

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7
Q

define critical concentration

A

the concentration of free ATP-G-actin at which assembly/disassembly are equal at one of the ends

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8
Q

what happens if:
above critical concentration
below critical concentration

A
  • the end will grow

- the end will shrink

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9
Q

what are the units for critical concentration

A

micromolar

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10
Q

what is + end CC

A

0.12 micromolar

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11
Q

what is - end CC

A

0.6 micromolar

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12
Q

what is treadmilling

A

rate of disassembly at one end is equal to rate of assembly at the other end

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13
Q

what regulates assembly and disassembly

A

actin-binding proteins

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14
Q

name 3 actin-binding proteins

A

profilin , Cofilin, thymosin beta4

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15
Q

what does profilin do?

A

enhances exchange of ADP for ATP on G-actin

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16
Q

what does Cofilin do?

A

enhances loss of ADP-actin from the -end

= facilitates disassembly

17
Q

what does thymosin beta4 do?

A

binds G-actin, to provide a reserve for actin when its needed for assembly

18
Q

what do capping proteins do

A

bind to filament ends - preventing assembly and disassembly

19
Q

name 2 capping proteins

A

CapZ and tropomodulin

20
Q

what do CapZ and tropomodulin do

A

CapZ = binds to and stabilises the + end

tropomodulin = binds to and stabilises the - end

21
Q

what does phalloidin toxin do

A

binds to f-actin preventing disassembly, can be used to stain actin (immunolabelling).
found in death cap mushroom

22
Q

name 2 actin cross-linking proteins

A

fimbrin (supports microvilli)

dystrophin (muscle cell cortex)

23
Q

what is dystrophin, and what happens in Duchenne muscular dystrophy

A

dystrophin is an adaptor protein that binds actin to cell-adhesion molecule dystroglycan

DMD = mutation impairs muscle function and shortens lifespan.

24
Q

what is the function of myosin

A

myosin uses ATP to generate movement to transport cellular components along actin filaments

25
Q

how many different types of myosin in the human body

A

40

26
Q

what does mutation to myosin II cause

A

familial hypertrophic cardiomyopathy

27
Q

how can you differentiate different types of myosin

A

all have similar head regions, but different tail regions, allowing them to move different distances

28
Q

what are the main structural differences between myosin V and myosin II

A

myosin V has longer necks, myosin V has globular cargo binding domains at its tail.

myosin II proteins can assemble into bipolar filaments that have contractile functions

29
Q

what does the neck domain do in myosin V

A

acts as a lever arm for the conformational change used in the power stroke

30
Q

where is myosin II found

A

muscles

31
Q

what is the role of titin

A

holds myosin in position

32
Q

what is the role of nebulin

A

holds actin filaments in position

33
Q

what does tropomyosin do

A

blocks the myosin head from interacting with actin

34
Q

what happens when calcium ions are released from the SR

A

calcium ions interact with troponin to induce a conformation change to tropomyosin, removing it from the myosin binding site = contraction

35
Q

describe the steps involved in the myosin power stroke

A
  1. ATP binds to myosin head, releasing it from actin
  2. hydrolysis of ATP > ADP + Pi = myosin head rotates into cocked state
  3. myosin head binds actin filaments
  4. release of P and elastic energy straightens the myosin molecule = moving the actin filament left
  5. ADP released, ATP binds = myosin head released
36
Q

what proportion of total protein in a typical animal is actin

A

5%

37
Q

what other process is reliant on actin, give an example

A

cell crawling = cell pushes forward via actin polymerisation

e.g. neutrophils migrating towards bacteria

211: Cell Biology (20 decks)

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