exam 4 Flashcards
(154 cards)
1
Q
what is actin structurally similar to?
A
MreB
2
Q
actin filaments are the subunit of what?
A
microfilaments
3
Q
what is the subunit of microtubules?
A
alpha-beta tubulin dimer
4
Q
of the three cytoskeleton filaments which is the thinnest and thickest?
A
thinnest: microfilaments (7-9 nm)
thickest: microtubules (25 nm)
5
Q
why are vesicles not lost in the cytoskeleton as they move to their target?
A
due to the pathway already established by microfilaments and microtubules guiding vesicles from location to location
6
Q
why do certain cells keep their structural integrity?
A
membrane is very thin, cytoskeletal elements provide a framework for the cell from the inside
7
Q
in what way do G actin subunits come to form polarized F actin filaments?
A
in a reverse assemble
8
Q
what is the composition of an F actin filament?
A
it is composed of two proto filaments
9
Q
where is the actin nucleotide binding site located?
A
on the negative end of each proto filament
10
Q
which end is the growing end on a F actin filament?
A
the positive end
11
Q
compare and contrast where the majority of microfilaments might be located on an epithelial vs migrating cell
A
epithelial: at the apical surface
migrating: at the filopodium
12
Q
present on the positive end, the ATP binding cleft on every actin is oriented toward the same end of the filament (T/F)
A
FALSE, the ATP binding site is on the negative end not positive
13
Q
if we ran an actin experiment on top of a nucleotide such as ATP, what else would we need?
A
ions such as Mg2+, K+, Na+
14
Q
how long will one single turn for an F actin microfilament be?
A
36 nm
15
Q
what purpose does magnesium serve in the polymerization of G actin subunits?
A
it serves as a catalyst
16
Q
what is nucleation?
A
the formation of an actin nucleus by 3 G actin monomers
17
Q
during the 3 phases of in vitro G-actin polymerization what do we want to happen?
A
nucleation, we want to start the process of creating a microfilament structure
18
Q
the nucleation phase is concurrent with what?
A
the lag phase, the nucleation phase is thermodynamically unfavorable and thus occurs gradually
19
Q
decreasing the amount of G actin will eliminate the nucleation phase and allow for faster entry into elongation (T/F)
A
FALSE, less G actin concentration will decrease nucleation but will NOT allow for shortcut to elongation. this could only happen if we have an initial addition of actin filament/nuclei/seeds
20
Q
only in the steady state do we have
A
10x speed on the positive end and the treadmill dynamic
21
Q
what is the steady state necessary for?
A
to help maintain a certain level of length for optimal activity
22
Q
elongation phase differs from steady state in that elongation allows for rapid assembly on each end of the filament (T/F)
A
TRUE, steady state has rapid assembly only on + end compared to - end but elongation phase grows from both ends
23
Q
what is critical concentration?
A
the concentration necessary for polymerization
24
Q
an actin concentration below the Cc would still result in a slight polymerization (T/F)
A
FALSE, Cc is all or nothing, we either reach it and polymerize or we don’t
25
how are steady state and Cc related?
both have filament assembly as a result of G actin addition and G actin disassembly being balanced
26
the equation for mass is?
total actin concentration - Cc
27
what is the Cc on the + end of F actin during actin treadmilling?
0.12 uM
28
how do we get the value for the + end of F actin during actin treadmilling?
rate of disassembly/rate of assembly (1.4/12)
29
what is the Cc of the - end of F actin during actin treadmilling?
0.6 uM
30
ratio for Cc on - end of F actin?
0.8/1.3
31
as a result of the steady state ratio of assembly and disassembly, what type of regions come about?
short region of ATP-actin and regions of ADP-Pi-actin toward the + end and ADP-actin toward the - end
32
treadmilling cannot do work in vivo (T/F)
FALSE, it can do work in vivo
33
what are the 3 actin binding proteins?
cyclin 1 profilin
cyclin 2 cofilin
cyclin 3 thymosin beta 4
34
compare and contrast cofilin and profilin
both: initially bind to an ADP-G actin
profilin: binds to sterically block ATP-G actin assembly at the - end
cofilin: binds 2-ADP-G actin monomers to induce a twist
35
which actin binding protein will enhance overall depolymerization?
cofilin because it twists off chunks of the F actin filament and creates new negative ends
36
how does the cell overcome excess ATP-G actin when there is no longer a need for elongation?
the thymosin beta 4 cycle buffers ATP-G actin by sequestering it during high concentration and releasing it in low concentration
37
what is the purpose of capping proteins?
they block assembly and disassembly at filament ends
38
+ capping proteins like CapZ and Gelsolin act on the + end of the growing filament to limit growth there in their own unique way (T/F)
TRUE
39
+ capping proteins CapZ and Gelsolin are under the control of PI(4,5)P2
FALSE, Gelsolin is under control of Ca+ concentration
40
what is the purpose of Gelsolin activity?
helps regulate actin that has grown past optimal limit
41
what does tropomodulin bind to?
binds to the - end of actin filament and tropomyosin
42
what is unique about tropomodulin capping?
stabilizes the filament
43
Arp2/3 helps in long filament formation
FALSE, formin helps in long filament formation
44
unlike Arp2/3, formin has multiple subunits
TRUE, there is the FH1, FH2, and RBD subunits and domains
45
what is unique about the nucleation that takes place with formin when compared to G actin?
G actin nucleation involves 3 subunits while formin nucleation by FH2 requires 2
46
what does FH2 bind to?
profilin-ATP-G actin
47
what amino acid is FH1 rich in?
it is proline rich
48
what is the purpose of FH1?
it acts as a landing site for profilin-ATP-G actin
49
CapZ binding will bind to the positive end of the filament and stop growing only after nucleation has started (T/F)
FALSE, CapZ can only affect FH2 domain before nucleation has occurred
50
what causes a formin protein to enter the active state?
an active RHO GTP will cause RBD to bind and activate the formin
51
what would happen if a mutation disables RHO?
RHO would be in a permanent inactive state and thus never allow for RBD binding. this would prevent activation of formin and reduce long filament formation
52
what would happen in a RBD mutation?
will prevent activation of formin
53
what would happen in a FH1 mutation?
decrease in profilin-ATP-G actin availability for FH2
54
what would happen if the FH1 amino acid (proline) was switched?
this will change the FH1 domain and prevent its function
55
what would happen in a FH2 mutation?
nucleation will be prevented and not protect against CapZ protein if a filament does end up forming. overall filament formation would be prevented.
56
what would happen in a profilin mutation?
this will not allow for essential subunits to be present for actin formation as ATP exchange is necessary
57
how are ATP G actin subunits transferred to the Arp2/3?
via the use of NPF
58
during branch assembly where are the ATP binding sites?
on the Arp2/3
59
what are the subunits of NPF?
W: Wh2
C: connector
A: acidic
60
what side of a ATP G actin binds to the Wh2 domain of NPF?
+ end
61
after binding a ATP-G actin on its + smooth head on the WH2 domain, the NPF will go on to bind the + end of existing actins to initiate branch growth
FALSE, once NPF binds atp G actin it will go to bind itself to the - end of an existing actin
62
NPF uses the connector domain to bind to the Arp2/3 complex
FALSE, the acidic domain does this
63
what fungal alkaloid plays a similar role to CapZ?
cytochalsin D
64
what does the sponge toxin latrunculin do?
it binds and sequesters G actin monomers
65
what toxin will enhance nucleation by binding and stabilizing actin dimers?
jasplakinolide
66
CDC25 and Rho are different classes of proteins
FALSE, both are membrane-bound G proteins
67
what domain of the Wasp protein is regulated by PI(4,5)P2?
the basic domain B
68
how does actin attach end to end to mebranes?
laterally
69
what is Wiskott-Aldrich syndome?
a skin condition resulting in a low platelet count, immune deficiencies and Eczema
70
where are fimbrin proteins located?
in the microvilli, filopodia, and focal adhesions
71
what is the diff b/w fimbrin and alpha-actinin?
fimbrin has (N) actin filament binding domain and alpha-actinin has a Ca2+ binding domain
72
what cross-linking protein is responsible for muscular dystrophy?
dystrophin
73
what is unique of the filamin corss-linking?
creates a loss of 3D network with gel-like properties
74
what cross-linking protein is responsible for providing spoke and hub structure?
spectrin
75
dystrophin is important for linking what?
membrane protein to actin cortex in muscles
76
what is unique of the dystrophin terminus?
it has a C terminus
77
what cross-linking protein is typical of stress fibers and the muscle Z line?
alpha actinin
78
how do we keep the structural integrity of multiple actin that are side by side?
via actin cross-linking proteins such as fimbrin which has N actin filament binding domain
79
what is unique about the spacer sequences in spectrin?
they have an alpha and a beta
80
myosin specificity comes from their different heads while the tail domain is preserved (T/F)
FALSE, there is a common head and specific tail
81
how many peptides are in the head complex of myosin 2?
6 peptides
82
how are the 6 peptides on the head complex divided?
2 heavy chains and 2 pairs of light chains (2 regulatory and 2 essential)
83
where does chymotrypsin cleave?
near the end of the heavy chain and by the regulatory light chain
84
what are the products of chymotrypsin?
a heavy meromyosin and light meromyosin
85
papain cleavage cuts directly at the regulatory light chain and heavy chain intersection creating a HMM and LMM product (T/F)
FALSE, it creates a S1 and S2 product
86
rank the myosin classes from largest step size to smallest
V (36nm), I (10-14nm), II (8nm)
87
what myosin class is responsible for organelle transport?
myosin V
88
the most common myosin class is ___________ responsible for _____________
myosin II, contraction
89
class I myosin is responsible for membrane association and exocytosis
FALSE, endocytosis
90
what is unique about myosin VI (6)?
it is the only myosin with a - end directed motor
91
what happens when ATP is bound to myosin?
a conformational change occurs releasing S1 head from actin
92
cocked stage is achieved by
hydrolysis of ATP into ADP + Pi
93
only in the cocked state will the myosin head perform a power stroke
FALSE, power stroke is accomplished by Pi release once cocked myosin attaches to actin
94
what causes rigor mortis?
a lack of ATP allowing for temporary binding. similarly, death prevents cell from pushing out calcium forcing muscles to contract
95
what is defined as a sarcomere unit?
Z disk to Z disk
96
why are Z disks important?
they establish the ideal amount of actin needed for a muscle and will cap this length
97
in addition to its regulation of gelsolin, magnesium plays a role in the contraction of myosin head as the walk towards the + end during high concentration (T/F)?
FALSE, calcium ions play a role in muscle contraction
98
sarcomere hold myosin actin filaments since they are the largest subunit of a muscle (T/F)
FALSE, sarcomere is the smallest subunit
99
how does the body prevent excessive overstretching?
via titin connection between Z disk and M band
100
nebulin will perform a similar role to titin in that it binds to actin to prevent excessive overstretching (t/f)
FALSE, nebulin binds to actin to determine optimal length
101
resting muscle calcium concentration?
< 10e-7 M
102
contracting muscle calcium concentration?
> 10e-6 M
103
the sarcoplasmic reticulum plays a role in thin and thick filament calcium dependent regulatory mechanisms via its release of cytosol/sacroplasm calcium (t/f)
FALSE, only the thin filament is subject to this
104
how do we propagate a nerve impulse signal from the neuromuscular junction throughout the muscle?
signal is propagated via transverse tubules across the sarcolemma
105
the MLCK phosphorylates the essential light chains of the myosin to activate it (t/f)
FALSE, it phosphorylates the regulatory light chain
106
how is myosin kept inactive during low concentration levels?
via the MLCP
107
describe a calcium-independent mechanism that will activate myosin
Rho kinase will activate myosin 2 by inhibiting MLCP
108
how does class 5 play a role with budding yeast?
it aids in cargo movement or organelles and higher components from mother cell to budding child
109
what role does myosin II play in the nucleus?
it helps bind the ends of cytoplasmic microtubules to orient the nucleus in preparation for mitosis
110
what are the characteristics of folded state of myosin V?
without cargo to bind the tails of myosin V, it will bind to each other and inactivate the motor head domain
111
what is the lamelipodium?
a cytoskeleton protein actin projection that generates force for advancement of leading edge
112
how does the lamellipodium extend?
via an Arp2/3 dependent mechanism
113
what mediates the connection between actin filaments and ECM proteins?
integrin
114
where does the actin-myosin II dependent contractions occur in the cell?
at the rear of the cell
115
in order to continue moving the cell will have to recycle integrins at the rear via an exocytic cycle that will transport them to the front (T/F)
FALSE, it is an endocytic cycle
116
branching filament create a connective net-like structure that allows for a high amount of contractile force to be withstood thus create stress fibers (t/f)
FALSE, stress fibers are created from long filaments
117
stress fibers make up the content of the leading edge and advance cells moving forward (t/f)
FALSE, the leading edge is made up of branched Arp2/3 complex
118
due to their vital role in activating both long and branched filament complexes, Rho family of GTPase are always found in the plasma membrane (t/f)
FALSE, the Rho family are known as peripheral membrane proteins and are kept inactive and away from the membrane until a signal reaches a receptor calling them to action
119
Rho proteins are kept inactive via GAP (t/f)
FALSE, GAP makes RHO inactive but is kept inactive by GDI
120
GEF activation of Rho will uncover what?
uncover membrane binding domain allowing for its attachment to the plasma membrane
121
GEF will hydrolyze GTP onto Rho (t/f)
FALSE, GAP hydrolyzes but GEF only performs the exchange from GDP to GTP
122
WASp and WAVE are both what?
NPF
123
Cdc45 is a unique Rho GTPase in that
it has dual action of activating Arp2/3 branched filament formation (with WASp) and Par6 polarizing properties
124
Cdc and Rac use NPF to activate Arp2/3 complex to create filopodia (t/f)
FALSE, Rac creates lamellipodia
125
how is Rho-GTP activated?
activation by Rac GTP and LPA signal molecule
126
filopodia and lamellipodium formation are independent (t/f)
FALSE
127
why does active Rho inhibit Rac activation?
to ensure no leading edge structures form at the rear of the cell
128
what mutation indicates a peripheral membrane ruffle formation?
a dominate-active Rac
129
what mutation does a dominant active Cdc42 result in?
a spiky membrane due to abundant filopodia
130
what mutation does a dominant active Rho cause?
formation of abundant stress fibers
131
assembled tubulin hydrolyzes ______
GTP
132
what is unique about the assembly of alpha beta tubulin?
it is dynamically unstable and polarized
133
all microtubules nucleated from MTOC remain anchored at the + end (t/f)
FALSE, they remain anchored by the - ends
134
all cytoskeletal subunits are highly polarized (t/f)
FALSE, intermediate filaments are unpolarized
135
what is the difference between alpha and beta tubulin?
alpha is stuck with GTP and nonhydrolyzable/non-exchangeable. beta has a nucleotide binding region that is hydrolysable and exchangeable so it can house GDP or GTP
136
calcium increases the affinity of the beta subunit for GTP with respect to GDP (t/f)
FALSE, it is magnesium
137
describe the arrangement of protofilaments
they are staggered to ensure alpha tubulin units are contacted with neighboring alpha tubulin except at the seam where alpha is attached to beta
138
the cytoplasm has a doublet protofilament structure (t/f)
FALSE, it has a singlet structure
139
where would you find a double protofilament structure?
in cilia and flagella
140
the centrioles and basal bodies have what kind of protofilament structure?
triplet
141
microtubule assembly is dynamically unstable but why?
the dynamic instability depends on the presence or absence of GTP beta tubulin cap
142
compare and contrast rescue and catastrophe GTP beta tubulin
rescue: GTP tubulin addition is greater than rate of GTP hydrolysis
catastrophe: rate of GTP hydrolysis is greater than rate of GTP tubulin addition
143
where is the microtubule built up from?
from the gamma tubulin ring complex
144
what are the 3 roles of MAP?
- stability at C term
- polymerization
- gap between microtubules
145
_______________ MAP causes instability
phosphorylated
146
what is a contributing factor to Alzheimer's?
Tau aggregation due to hyperphosphorylation
147
kinesin 13 only binds to the + end (t/f)
FALSE, it prefers to bind to the + end but it will also bind to the -
148
which disassembly protein binds to curved positions of the proto filament?
Op13/stathmin
149
Op18/stathmin removes a dimer just like kinase 13 (t/f)
FALSE, it removes a pair of dimers
150
which kinesins perform a walking motion?
kinesins 1 and 2
151
what happens if dynamitin is overexpressed?
explosion of cell
152
what would a defective kinesin 2 result in?
accumulation of particles in the - end
153
when might tubulin and kinesin 13 be present?
during mitosis
154
mitosis has microtubule instability due to what?
inhibition of XMAP2
