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Cells: Form and Function > 18-19 > Flashcards

18-19 Flashcards

1
Q

cytoskeleton is fixed and not dynamic (t or f)

A

false

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2
Q

compare microfilaments and microtubules (3)

A

microfilaments: composed of actin, organized into functional bundles by actin binding proteins, may serve as tracks for ATP powered myosin motor proteins
microtubules: composed of tubulin, extend through the cell and provide organizational framework, may serve as tracks for ATP powered kinesins and dyneins, motor proteins

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3
Q

how are signals for arrangement detected during regulation of cytoskeleton function?

A

detected by cell surface receptors that activate signal transduction pathways

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4
Q

what happens in the absence of the signals for arrangement of cytoskeleton?

A

cells are not polarized

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5
Q

microfilament s have a _____ assembly

A

reversible

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6
Q

each actin molecule contains a ___ ion complexed with either ___ or _____

A

mg2+, ATP or ADP

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7
Q

actin exists in what two forms?

A

globular polymer and G actin filamentous polymer

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8
Q

actin is a ATPase meaning?

A

hydrolyzes ATP to ADP

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9
Q

beta actins are present where?

A

cell cortex

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10
Q

y actins are found where?

A

stress fibres

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11
Q

describe G actin

A

monomer separated into two lobes by a deep cleft, addition of cations mg2+, K+, Na+ induces filament formation

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12
Q

describe F actin

A

arranged in helical strands wound arround eachother, + end favoured for addition of subunits, - end favoured for subunit dissociation

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13
Q

does myosin s1 + actin bind microtubules?

A

no

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14
Q

actin binding proteins contribute to_______ and _______ of filaments

A

stability and dissasembly

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15
Q

what are the 3 stages of actin polymerization? (describe each one)

A
  1. nucleation phase: lag period where G actin subunits combine into an oligomer of 2-3 subunits
  2. elongation phase: short oligomer rapidly increases and grows at both ends, concentration of G actin decreases until equilibrium is reached between filaments and monomers
  3. steady state phase: rate of polymerization=rate of assembly , no net change in total length
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16
Q

what is critical concentration cc?

A

below which filaments cannot assemble, above what filaments can form

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17
Q

what is steady state?

A

concentration of monomeric actin remains at critical concentration, rate of assembly and dissociation equal

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18
Q

do actin filaments grow faster at the + or - end?

A

much faster at the + ends

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19
Q

describe actin treadmilling

A

above C+ subunits are added to the + end and net growth occurs, but below C+ subunits are lost from the - end and shrinkage occurs, when ATP G binds to + end, ATP is hydrolyzed to ADP and P actin undergoes a conformational change based on ATP vs ADP binding

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20
Q

actin tread milling is powered by?

A

ATP hydrolysis

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21
Q

what is the function of profilin?

A

to keep all free G actin in ATP bound state, can also bind proline rich proteins while binding actin, yeilds profiling atp actin complex

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22
Q

how does profilin function and what does it bind?

A

binds G actin on opposite side of the ATP binding cleft, when bound ADP G actin it opens the cleft and enhances loss of ADP

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23
Q

what is the function of coffilin?

A

binds ADP F actin

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24
Q

how does coffilin function?

A

binds two actin monomers and changes twist of filament, filament breaks with more - ends, can be dissasembled

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25
Q

together profilin and cofilin ______ treadmilling in vitro

A

enhance

26
Q

what is thymosin B4?

A

actin monomer sequestering protien

27
Q

how does thymosin B4 function?

A

holds excess actin monomers, lower unpolymerized actin concentration to prevent unwanted filamentation, binds ATP G actin so it can be added to either filament end

28
Q

name the 3 actin binding proteins?

A

profilin, coffilin and thymosin B

29
Q

what is the rate limiting step of actin filament assembly?

A

formation of initial actin nucleus

30
Q

what do capping proteins do?

A

prevent continual growth and dissasembly in uncontrolled environment

31
Q

what are the two classes of capping proteins? (describe each)

A
  1. CapZ ( binds + end, very high affinity, rapids caps, allow filament growth when needed by inhibition of other proteins)
  2. Tropomodulin (binds - end, inhibits assembly and disassembly, works with tropomyosin to stabilize filaments)
32
Q

what are actin nucleating proteins controlled by?

A

signal transduction pathways

33
Q

what is the purpose of the FH2 domain?

A

protects the + end from being immediately capped by end capping proteins such as CapZ

34
Q

how must the arp2/3 complex be activated?

A

by nucleation promoting factor (NPF) and associate with side of existing actin

35
Q

NPF has a WCA, domain what is this?

A

WH2 binds actin, C connector, A acidic

36
Q

if a - end of a microfilament is fixed in the cell, objects bound to the + end ___ across the cell

A

ride

37
Q

filament grow at their __ end until capped by ______

A

+, capZ

38
Q

how does listeria use actin polymerization to move?

A

ActA bacterial cell surface protein functions like NPF to activate Arp2/3 complex, VASP protein enhances rate of motility

39
Q

how does VASP enhance the rate of motility in listeria?

A
  1. proline rich region enhance polymerization by recruiting profilin ATP G actin , holds onto newly formed filament, protects the + end of filament from capping by cap Z
40
Q

how is clathrin mediated?

A

endocytosis assembly factors recruit NPFs that activate Arp2/3 complexes, burst of Arp2/3 dependent actin assembly drives internalized endocytic vesicles away from plasma membrane

41
Q

what are 3 ways toxins can affect actin?

A
  1. cytochalasin D from fungus blocks + end
  2. latrnculin from sponges sequesters G actin
  3. phalloidin from mushroom locks subunits together in filaments
  4. jasplakinolide from sponges enhance nucleation
    * may promote depolymerization of filaments
42
Q

during attachment of microfilaments to membrane, what does ankyrin molecules do?

A

link spectrin tetramer to band 3 integral membrane protein

43
Q

during attachment of microfilaments to membrane, what does band 4.1 do?

A

links hub actin filaments and spectrin ends to glycoprotein

44
Q

during attachment of microfilaments to membrane, what does ezrin do?

A

activated by phosphorylation, links actin filaments laterally to microvillar plasma membrane, indirect attachment through EBP50 or direct attachment to cytoplasmic regions

45
Q

myosins move along ____ filaments

A

actin

46
Q

where were myosins first discovered?

A

skeletal muscle

47
Q

what is the structure of myosin II?

A

6 polypeptide units, two identical heavy chains, two identical light chains

48
Q

what does limited proteolytic cleavage of myosin II do?

A

generates tail fragments LMM S2 and S1

49
Q

what is the general myosin structure?

A

all have head and neck domain

50
Q

_____ domain of myosin defines what is moved

A

tail

51
Q

what are the 3 classes of myosins and where do they move?

A

I, II , V they move toward the + end of actin filaments

52
Q

describe myosin I

A

only single headed myosin, one heavy chain with head and neck domain, encoded by 8 human myosin genes

53
Q

describe myosin V

A

two head domains, six light chains per neck, encoded by 3 myosin genes

54
Q

how does myosin move?

A

using the cross bridge cycle for coupling ATP hydrolysis to each force producing step along actin filament

55
Q

myosin V bound cargo is best studied in _______

A

yeast

56
Q

myosin V bound cargo transports vesicles and organelles along______

A

microtubules

57
Q

how does myosin V release cargo?

A

inactive state where head and tail domain bind

58
Q

how does myosin V transport organelles and secretory vesicles in yeast?

A

along actin filaments nucleated by formins into the bud before cell division

59
Q

myosin V bound cargo binds the ends of cytoplasmic microtubules to orient the nucleus in preparation for _______

A

mitosis

60
Q

what are the 4 steps of locomotion?

A

extension, adhesion, translocation, de adhesion and endocytic recycling

61
Q

during locomotion extension occurs with______ adhesion occurs with _______ translocation occurs with ________ and de adhesion occurs with ______ _______

A

Arp2/3, integrin, myosinII, endocytic recycling

Cells: Form and Function (6 decks)

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