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Cell biology > week 7 > Flashcards

week 7 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

cell movement

A
  • involves polymerization and depolyemerization of actin
  • actin is responsible for cell shape and movement of organelles under the PM
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2
Q

actin functions

A
  • found in epithelial cells (in microvilli)
    -cortical actin cells
  • contratile belt structures
  • cell migration
  • actin involved in moving things inside the cell
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3
Q

actin structures

A
  • bundles in microvilli
  • networks and bundles cortical actin
  • form fillapodia, stress fibres
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4
Q

monomers of actin

A

G-actin

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5
Q

types of actin

A

alpha (muscle)
beta (cortex)
gamma (stress fibres)
- all are functionally the same

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6
Q

g actin

A

four domains
- atp binding cleft
- polarity bc unsymmetrical

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7
Q

polyermize G actin to make…

A

F actin

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8
Q

orientation of polymerization of g actin monomers

A

atp binding cleft points thhe same way , always located towards the negative end

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9
Q

which side polymerizes faster

A

the + end

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10
Q

double helix formation of actin filaments

A
  • loop of 36 nm, presents a g actin every 36 nm
  • g actin is polar, so f actin is therefore polar
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11
Q

myosin s1 experiments

A
  • the myosin s1 that coats the actin monomers, shows a pattern of arrowheads that always point towards the + end
  • this allows us to fid the - an + end
  • this also stabilizes anti (cannot depolyermize)
  • this can be used a a flagellar nucleus
  • u can get polymerization by actin monomers above a certain cocentration
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12
Q

above critical concentation

A

polymeriation

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13
Q

what does teh speed of poymernzation depend on

A

the presence of nuclei

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14
Q

actin monomers must be bound to ____ in order to polyemrize

A

atp
- will polymerzie and the hydrolysis of ATP after polymerization NOT BEFORE

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15
Q

critical concentration for + end

A

0.12

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16
Q

critical concentration for - end

A

0.8
- needs much more actin

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17
Q

above both critical concentration

A

polymrization

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18
Q

below both critical coentaration

A

depolyermize both sides

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19
Q

in between the critical concentrations

A
  • polymrerizaiton at + end for ex, and not at - end, meaning treadmilling, were ]
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20
Q

when does tread milling occur

A
  • when one side is growing only
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21
Q

what is C+ c?

A
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22
Q

how do we regulate large stores of actin/actin polymerization

A
  • thymosin
  • profilin
  • cofilin
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23
Q

thymosin

A

sequesters g actin, binds most of the g actin, removes from critical ceonctnreation so that it is not available for polymerizationn aymore
- sequesters actin and provides a reservoir

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24
Q

profilin

A

takes.g acting in the ads form to turn to g actin in atp form

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25
Q

cofilin

A
  • causes depolyemizaiton of actin filaments
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26
Q

actin capping proteins

A

cap z
tropomodulin

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27
Q

cap z

A
  • binds to + end
  • this end does not polyermize or depolymerize when presenttr
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28
Q

tropomodulin

A
  • binds to - end and does same thing as caps
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29
Q

where would capping proteins be found

A
  • ## in muscle fibres
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30
Q

cytochalasin:

A

depolyermizes actin filaments,

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31
Q

phalloidin

A

stabilizes actin filamentsactin

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32
Q

actin disrupting drugs

A

drugs that can be used to stabilize/destabiilize actin filaments

33
Q

formins

A

nucleating proteins
- regulate assembly of unbranched filaments by acting on the + end
- providing nuclei
- nucleating proteins allow polyermization to occur

34
Q

how is forming activated

A

by a protein called rho gtp

35
Q

where is rho gtp found

A

at the plasma membrane, can activate forming the in the gTP form, this is where polymerization willl cocur

36
Q

when can polymerization occur through formin

A

Forman activated by rhogtp, polymerization, if g actin is above vciritcal concentration and in atp form (profilin needed)

37
Q

arp23

A
  • mediates filament branching
  • allows actin to form branched filaments
38
Q

how does arp23 work

A

needs nucleation promoting factor such as WASp or WAVE

39
Q

how are WASP and WAVE activated

A

by cdc42 and Rac

40
Q

how does listeria use this mechanism

A
  • it has ACT protein that activates arp 23 to cause rapid branching that will allow it to burst through the PM
  • no need for cdc42 or rac
41
Q

what is a function of arp2/3 dependent actin assmebly (endocytosis)

A

in endocytosis actin polymerization can move membrane, one dnoytosis, the plasma membrane can be pulled into the cell to form a vesicle that is moving into teh ell. polymerizing pulls on the membrane (keep adding to positive end of actin)
- the vesicle moves deeper away from pm

42
Q

ARP2/3 function in [haogycotsisi

A
  • actin can pull a membrane inward, or push a membrane outward
43
Q

what sorts of structures can actin form

A

bundles or networks

44
Q

Fibrin and alpha actinin

A

cause bundling of parallel actin microfilaments

45
Q

how are RBCs supported

A

the biconcave shape is due to teh actin network that is holding the Plasma membrane of the RBC

46
Q

ankyrin

A

actin network binding proteins that support teh cell memrbane

47
Q

ezrin

A
  • bundles of actin
  • link the bundles to the Plasmam membrane using ezrin
48
Q

dystrophin

A
  • link plasma membrane of muscle cells so that dystrophin can pull when muscle contracts
49
Q

muscular dystrophy

A
  • repeated damage to muscle, leading to dysfunctional dystrophin
  • cannot regenerate muscle anymore
50
Q

myosin

A
  • actin’s motor protein
51
Q

what is the most abundant myosin

A

myosin 2

52
Q

myosin heavy chainchain

A
  • heavy chain with head, neck and tail
  • ehad binds actin, and uses atp to move to plus end by doing binding and atp hydrolysis
  • neck domain bends
  • tail domain attaches to cargo
53
Q

what is myosin composed of

A

heavy chain, and light chains\
- the head is an atpASE
- NECK BINDS LIGTH CHAIN
- tail binds cargo

54
Q

light chains of actin

A
  • involved in binding to teh neck region
55
Q

imporance of neck region in light chain

A
  • the neck region is involved in determining how fast myosin moves
  • it is regulated/faciliated by the binding of light chaisns to the neck region, regulates how fast or slow the myosin moves
56
Q

myosin classes

A

myosin 1, 2, 5

57
Q

myosin 1

A
  • heavy chain acts as a monomer does not form dimer
  • neck binds light chains to regulate meovement, tail binds to phospholipids in membranes
  • involved in endocytosis
  • hols actin at the plasma membrane and supports it
  • can hold on to membrane or just support
58
Q

myosin 2

A
  • is found in muscle, involve din muscle contraciton
  • forms structure with overlapping tails and heads found on either side
59
Q

myosin 5

A
  • dimer of two heavy chains
    involved in vesicular transport
  • the tail region has a variable domain
  • can bind to different types of vesicles
  • doesn’t use light cahins
  • transport vesicles towards the plus end of atin
  • long neck region and lots of light cahins
  • takes the longest steps bc long neck
  • can bind PM like myo 1 either for transport or just for support
60
Q

length of myosin 5 steps

A

72 nm

61
Q

what determines the rate of movement myosin 2

A

length of neck

62
Q

sliding-filament assay used to detect myosin powered movement

A
  • taking fragments of what needs to be studied from the myosin and digesting it in different ways
  • once added to glass cover slip, should stick to it
  • add flureoscently labelled actin, that can be visualized under fluorescent mciroscope
  • add different things to see what is required for movement (i.e. add ATP,
63
Q

what is the point of teh sliding filament assay

A

this is how we understand that the neck is important for velocity, which is regulated by the light chains. longer neck = faster velocity, since more light chains are allowed to bind.

64
Q

rigger state

A

myosin in ADP form is bound to actin, will not move until ATP is added.

65
Q

power stroke

A

myosin head pushes teh actin )-) end towards the left, now the Pi leaves
- atp binds, let go, hydrolysis, power stroke, back to rigorous state `

66
Q

sarcomere

A
  • distance between z discs, and in-between is teh a band and I band ( the a band is dense) and the I band (less dense
67
Q

z discs

A

hold the actin mcirofialemnts that are extending into the middle of teh sarcomere

68
Q

middle of sarcoma

A

myosin thick filaments,

69
Q

a band

A

two myosin heavy chains, thick filaments that have their heads between the actin microfilaments,

70
Q

what happens to the z discs/sarcomere during muscle contraction

A

-

71
Q

are the actin microfilaments stable

A
  • they must be stable
    (dont want actin and sarcomeres to depolymerize)
  • caps at plus end at z disc
  • tropomodulin caps the - ends
  • nebulin coating also helps in stability
  • titin
72
Q

titin

A

holds the myosin thick filaments in the centre.
- these molecules are squished when contractionn occurs
- relax, titin expands a bit wihich helps in pushing the sarcomere apart

73
Q

sarcolemma

A
  • plasma membrane surrounding a muscle cell
74
Q

transverse tubtules

A

projections of the memraben that reach deep into the cell
- they are in close contact with the SR

75
Q

SR

A

stores calcium
- surrounds sarcomeres

76
Q

voluntary muscle contraction leads to

A
  • nerve impulses, (electrical changes in PM)
  • the nerve impulse comes down, hits the pM, EXTENSION OF T TUBULE,
  • opening of calcium channels, release of Ca from Sr
  • this helps facilitate muscle contraction
77
Q

troponin and tropmyosin

A

coat actin in a way where biding nd inhibiting the myosin binding sites.

78
Q

how is movement of T and T triggered

A

by calcium release. opening of binding site, and myosin can take a step

79
Q
A

Cell biology (15 decks)

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