week 7 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
cofilin
- causes depolyemizaiton of actin filaments
26
actin capping proteins
cap z tropomodulin
27
cap z
- binds to + end - this end does not polyermize or depolymerize when presenttr
28
tropomodulin
- binds to - end and does same thing as caps
29
where would capping proteins be found
- in muscle fibres -
30
cytochalasin:
depolyermizes actin filaments,
31
phalloidin
stabilizes actin filamentsactin
32
actin disrupting drugs
drugs that can be used to stabilize/destabiilize actin filaments
33
formins
nucleating proteins - regulate assembly of unbranched filaments by acting on the + end - providing nuclei - nucleating proteins allow polyermization to occur
34
how is forming activated
by a protein called rho gtp
35
where is rho gtp found
at the plasma membrane, can activate forming the in the gTP form, this is where polymerization willl cocur
36
when can polymerization occur through formin
Forman activated by rhogtp, polymerization, if g actin is above vciritcal concentration and in atp form (profilin needed)
37
arp23
- mediates filament branching - allows actin to form branched filaments
38
how does arp23 work
needs nucleation promoting factor such as WASp or WAVE
39
how are WASP and WAVE activated
by cdc42 and Rac
40
how does listeria use this mechanism
- 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
what is a function of arp2/3 dependent actin assmebly (endocytosis)
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
ARP2/3 function in [haogycotsisi
- actin can pull a membrane inward, or push a membrane outward
43
what sorts of structures can actin form
bundles or networks
44
Fibrin and alpha actinin
cause bundling of parallel actin microfilaments
45
how are RBCs supported
the biconcave shape is due to teh actin network that is holding the Plasma membrane of the RBC
46
ankyrin
actin network binding proteins that support teh cell memrbane
47
ezrin
- bundles of actin - link the bundles to the Plasmam membrane using ezrin
48
dystrophin
- link plasma membrane of muscle cells so that dystrophin can pull when muscle contracts
49
muscular dystrophy
- repeated damage to muscle, leading to dysfunctional dystrophin - cannot regenerate muscle anymore
50
myosin
- actin's motor protein
51
what is the most abundant myosin
myosin 2
52
myosin heavy chainchain
- 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
what is myosin composed of
heavy chain, and light chains\ - the head is an atpASE - NECK BINDS LIGTH CHAIN - tail binds cargo
54
light chains of actin
- involved in binding to teh neck region
55
imporance of neck region in light chain
- 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
myosin classes
myosin 1, 2, 5
57
myosin 1
- 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
myosin 2
- is found in muscle, involve din muscle contraciton - forms structure with overlapping tails and heads found on either side
59
myosin 5
- 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
length of myosin 5 steps
72 nm
61
what determines the rate of movement myosin 2
length of neck
62
sliding-filament assay used to detect myosin powered movement
- 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
what is the point of teh sliding filament assay
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
rigger state
myosin in ADP form is bound to actin, will not move until ATP is added.
65
power stroke
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
sarcomere
- 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
z discs
hold the actin mcirofialemnts that are extending into the middle of teh sarcomere
68
middle of sarcoma
myosin thick filaments,
69
a band
two myosin heavy chains, thick filaments that have their heads between the actin microfilaments,
70
what happens to the z discs/sarcomere during muscle contraction
-
71
are the actin microfilaments stable
- 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
titin
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
sarcolemma
- plasma membrane surrounding a muscle cell
74
transverse tubtules
projections of the memraben that reach deep into the cell - they are in close contact with the SR
75
SR
stores calcium - surrounds sarcomeres
76
voluntary muscle contraction leads to
- 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
troponin and tropmyosin
coat actin in a way where biding nd inhibiting the myosin binding sites.
78
how is movement of T and T triggered
by calcium release. opening of binding site, and myosin can take a step
79