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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
together profilin and cofilin ______ treadmilling in vitro
enhance
26
what is thymosin B4?
actin monomer sequestering protien
27
how does thymosin B4 function?
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
name the 3 actin binding proteins?
profilin, coffilin and thymosin B
29
what is the rate limiting step of actin filament assembly?
formation of initial actin nucleus
30
what do capping proteins do?
prevent continual growth and dissasembly in uncontrolled environment
31
what are the two classes of capping proteins? (describe each)
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
what are actin nucleating proteins controlled by?
signal transduction pathways
33
what is the purpose of the FH2 domain?
protects the + end from being immediately capped by end capping proteins such as CapZ
34
how must the arp2/3 complex be activated?
by nucleation promoting factor (NPF) and associate with side of existing actin
35
NPF has a WCA, domain what is this?
WH2 binds actin, C connector, A acidic
36
if a - end of a microfilament is fixed in the cell, objects bound to the + end ___ across the cell
ride
37
filament grow at their __ end until capped by ______
+, capZ
38
how does listeria use actin polymerization to move?
ActA bacterial cell surface protein functions like NPF to activate Arp2/3 complex, VASP protein enhances rate of motility
39
how does VASP enhance the rate of motility in listeria?
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
how is clathrin mediated?
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
what are 3 ways toxins can affect actin?
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
during attachment of microfilaments to membrane, what does ankyrin molecules do?
link spectrin tetramer to band 3 integral membrane protein
43
during attachment of microfilaments to membrane, what does band 4.1 do?
links hub actin filaments and spectrin ends to glycoprotein
44
during attachment of microfilaments to membrane, what does ezrin do?
activated by phosphorylation, links actin filaments laterally to microvillar plasma membrane, indirect attachment through EBP50 or direct attachment to cytoplasmic regions
45
myosins move along ____ filaments
actin
46
where were myosins first discovered?
skeletal muscle
47
what is the structure of myosin II?
6 polypeptide units, two identical heavy chains, two identical light chains
48
what does limited proteolytic cleavage of myosin II do?
generates tail fragments LMM S2 and S1
49
what is the general myosin structure?
all have head and neck domain
50
_____ domain of myosin defines what is moved
tail
51
what are the 3 classes of myosins and where do they move?
I, II , V they move toward the + end of actin filaments
52
describe myosin I
only single headed myosin, one heavy chain with head and neck domain, encoded by 8 human myosin genes
53
describe myosin V
two head domains, six light chains per neck, encoded by 3 myosin genes
54
how does myosin move?
using the cross bridge cycle for coupling ATP hydrolysis to each force producing step along actin filament
55
myosin V bound cargo is best studied in _______
yeast
56
myosin V bound cargo transports vesicles and organelles along______
microtubules
57
how does myosin V release cargo?
inactive state where head and tail domain bind
58
how does myosin V transport organelles and secretory vesicles in yeast?
along actin filaments nucleated by formins into the bud before cell division
59
myosin V bound cargo binds the ends of cytoplasmic microtubules to orient the nucleus in preparation for _______
mitosis
60
what are the 4 steps of locomotion?
extension, adhesion, translocation, de adhesion and endocytic recycling
61
during locomotion extension occurs with______ adhesion occurs with _______ translocation occurs with ________ and de adhesion occurs with ______ _______
Arp2/3, integrin, myosinII, endocytic recycling

Cells: Form and Function (6 decks)

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