Exam 3 Flashcards
1
Q
Actin filaments underlie the plasma membrane and provide…
A
strength and shape to the lipid bilayer
2
Q
3 types of transient structures formed by actin
A
- lamellipodia & filopodia
- contractile ring
- growth cones
3
Q
actin filaments form _ when stabalized by _
A
form stiff and relatively permanent structures when stabilized by actin binding proteins
4
Q
_ increase the surface area of intenstinal epithelial cells
A
microvilli
5
Q
actin filament subunits
describe structure
A
Globular actin (G-Actin) assemble head-to-tail to form protofilaments (F-actin) and F actin twist around each other to form actin filament
6
Q
F-actin _ to form actin filaments
A
twist around each other in a right handed helix
7
Q
each G actin has a _
A
binding site for ATP
8
Q
actin filaments are similar to microtubles because they are
5 things
A
- found in all eukaryotes
- polar
- dynamic unless cap
- nucleation is rate limiting step
- filament grow more rapidly at plus end
9
Q
barbed end is the _ while pointed is the _
A
plus end, minus end
10
Q
latrunculin
A
binds actin monomers and
results in filament depolymerization
11
Q
phalloidin
A
binds to and stabilizes actin filaments, causing a net increase in polymerization
12
Q
Subunits bound to thymosin…
A
can’t add to either end of a filament, or hydrolyze/exchange their bound nucleotide
no addition to filament
12
Q
Subunits bound to thymosin…
A
can’t add to either end of a filament, or hydrolyze/exchange their bound nucleotide
no addition to filament
13
Q
profilin
A
Profilin binds to the end of a subunit which would normally add to the minus end of a filament, leaving exposed the site on the monomer that binds to the plus ends of filaments
14
Q
Thymosin and profilin…
A
cannot bind to the same actin monomer at the same time
compete for binding
15
Q
Activation of a small amount of profilin…
A
can produce rapid filament assembly
1. Profilin binds to monomers which are transiently released by thymosin
2. Profilin-bound monomers are then added to the plus ends of actin filaments
3. Once bound to a filament, the profilin is released and recycled for further rounds of filament elongation
16
Q
two ways how profilin is regulated
A
- profilin phosphorylation
- profilin binding to inosol phospholipids
17
Q
Arp 2/3 complex do what
A
nucleates the assembly of branched networks of actin filaments
18
Q
Arp 2/3 steps
A
- in absense of activating factor, Arp 2 & 3 are held together by accessory proteins in a conformation that prevents nucleation
- activating factor binds to the complex & conformational change
- Arp2/3 nucleation by binding to minus end of the actin filament
19
Q
Arp 2/3 complex is formed from
A
two actin related proteins (ARPs)
20
Q
Arp 2/3 complex is most efficient at nucleating filament growth when ___ resulting in the formation of
A
it is attached to the side of a preexisting actin filament at a 70 angle,
branched actin networks
21
Q
formins
do what
A
nucleate the growth of straight, unbranched filaments which can be crosslinked by accessory proteins
* each formin subunit binds one actin monomer
* as filament grows, formin remain on plus end
* remains attached even as new protofilaments are added
22
Q
Nucleation of actin filaments often occus at _ resulting in _
A
occurs at or near the plasma membrane, resulting in a high density of actin filaments at the cell periphery.
23
Q
cell cortex
A
actin rich region just benath the plasma membrane
24
microvilli and filopodia
spiky projections formed from parallel bundles of
actin filaments
25
lamellipodia
flat protrusive veils that help move cells over solid substrates
26
tropomyosin
a. Elongated protein which binds simultaneously to six or seven adjacent subunits
b. Prevents interaction of actin filament with other proteins (e.g. myosin motors)
c. Important component of muscle sarcomeres
27
capping proteins...
bind to the ends of actin filaments to slow the rate of filament growth and depolymerization
28
gelsolin...
severs actin filaments
29
after severing, gelsolin...
remains attached to the actin filament and caps the new plus ends
30
gelsolin is activated by
high levels of cytosolic Ca
31
gelosin proteins structure
1. one domain that binds to an exposed region on filament
2. second domain binds to a region that is normally hidden
32
how is it proposed that gelsolin molecules work
they bind to surface of a filament and wait until the hidden binding site is exposed because of a temp flunctuation
the insertation of second domail - breakage
33
cofilin _ by _
| does what and how
* destabilized actin filaments
* it binds along the length of an actin filament and forces the filament to twist more tight
* this weakens contacts between actin subunit and makes the filament brittle
* severed ends undergo rapid deploymerization
34
cofilin preferentially binds _
ADP containing actin filaments, so older filaments
35
Bundling proteins
Proteins which cross-link unbranched actin filaments into parallel arrays
36
alpha actinin is a
bundling protein which produces loosely packed bundles of oppositely polarized actin filaments, leaving sufficient space for addition of myosin 2
37
alpha actinin are found in
stress fibers and contractile bundles
38
fimbrin
Bundling protein which promote the formation of tightly-packed, non-contractile actin filament bundles
39
fimbrin bundles _ myosin 2
exclude
| tightly packed
40
Gel-like networks are formed from
branched filaments nucleated by Arp 2/3 complexes
41
gel forming proteins have
long, bent linkages between actin binding domains, resulting in formation of 3d actin gels
42
filamin
Gel-forming protein which cross-links actin filaments at right angles to promote the formation of web-like networks with the consistency of highly viscous gels; these proteins are necessary for the formation of the lamellipodia used by cells to crawl across a solid surface
43
filamin is necessary for
the formation of the lamellipodia used by cells to crawl across a solid surface
44
spectrin structure
long flexible composed of two alpha and two beta subunits with actin binding sites
45
spectrin forms
2d network under plasma membrane of red blood cells
46
spectrin molecules are held together by
a protein complex whhich includes short actin filaments
47
the heavy chains of myosin motors
contain globular head domains which control filament binding specificity, and hydrolyze ATP to provide the energy for movement.
48
c-termini of heavy chain of myosin
* form long coiled tails
* bind to cargo and other myosin heavy chains to make dimers
49
what allows mysosin to bind to other cargo
tail sequences being diverse
50
_ is very important to construction and function of stereocilia
myosin
51
mutations in myosin are known to cause
deafness
52
the motor activity of myosin is localized to
S1 fragment
53
S1 fragment
Myosin motor domains released by digestion of thick filaments with chymotrypsin and papain; motor activity is localized to this fragment
54
S1 fragment
Myosin motor domains released by digestion of thick filaments with chymotrypsin and papain; motor activity is localized to this fragment
55
how does myosin 2 move along actin
1. first the myosin is in rigor (no nucleotide and head attached to filament)
2. ATP binding = release of filament
3. hydrolysis displaces the head, moves the lever arm forward
4. head binds to new site, lever & head back to normal position, causes power stroke bc rest of myosin pulled forward
5. back to rigor conformation
56
atp causes changes in _ in myosis
actin binding affinity
57
ATP binding causes myosin motor head to
release actin
58
myosin 2 functions in
* cytokinesis
* cell locomotion
* muscle contraction
59
myosin 2 forms dimmers by
alpha helical tail domains of two heavy chains wrap around each other to form coiled tail of dimer
60
myosin two dimers form
striated muscle cells as bipolar thick filaments
* coiled coil bundle with other coils
* heads are oreintated opposite direction at the two ends
61
all the muscle types depend on
ATP driving sliding of arrays of actin filaments against arrays of myosin 2 filaments
62
all the muscle types depend on
ATP driving sliding of arrays of actin filaments against arrays of myosin 2 filaments
63
skeletal muscle is in charge of
voluntary movement
64
smooth muscle in charge of
involuntary contraction of gut walls
65
skeletal muscles are formed by _ and consist of _
formed by fusion of myoblasts and cytoplasm is filled with myofibrils
66
myofibrils are composed of
repeating contractile units called sarcomeres
67
sarcomeres contain
| general
overlapping arrays of thin (actin) and thick (myosin 2) filaments
68
a bands of sarcomeres
span the length of the thick myosin filaments, contains overlapping thin filaments
69
m lines of sarcomeres
link thick filaments into hexagonal lattices
70
I band sarcomeres
the potions of thin filaments that do not overlap thin filaments
71
z discs sarcomeres
cap plus ends and bundle thin filaments, boundry of sacromeres
72
the uniformity and stability of sarcomeres is due to
| general
accessory proteins
73
_ stabalizes plus ends of thin falments in sarcomeres
CapZ
74
tropomodulin
stabilizes minus ends of thin filaments of sarcomere
75
nebulin
determines length of thin filaments of sarcomere
76
titan
positions thick filaments of sarcomere midway between z discs
* acts like a spring, unfolds when muscle is stretched
77
thick filaments of sarcomeres are arranged in
a hexagonal latttice
78
sarcomeres muscle contraction what happens and how
* bipolar myosin thick filaments walk towards plus ends of sets of actin thin filaments with opposite polarity
* thick and thin filaments slide past each other
* sarcomeres shorten as the overlap of the thick and thin filaments increases
79
t-tubules
* folds of the plasma membrane that extend inwards and surround each myofibril
* convey action potentials down into the cell
80
sarcoplasmic reticulum
storage site for intracellular Ca in muscle cells
* surround myofibrils
81
when t tubule is depolarized...
* voltage gated Ca channels in t tubules open and CA in cell
* This triggeres opening of Ca release channels in sarcoplasmic reticulum, more Ca in cytosol
* contraction
* transient increase: ATP dependent Ca pumps in SR membrane return Ca levels to normal
82
tropomysin does what
prevents myosin from binding to thin filaments
83
how does troponin complex work
* in resting muscle, tropomyosin molecules bind alon actin filaments and mask myosin binding sites
* when Ca cytosol up, troponin C binds Ca and troponin I release its hold on actin
* tropomyosin shifts its position, causing myosin binding sites to be exposed
84
regulation of smooth muscle contraction process
* activation of cell surface receptors triffers release of Ca from sarcoplasmic reticulum
* Ca binds to calmodulin
* calmodulin binds to myosin light chain kinase (MLCK)
* MLCK phsophorylates regulatory myosin light chain
* smooth msucle contracts
85
contraction causes smooth muscle cells to _ in length
decrease
86
in non muscle contractile cells, myosin 2
* present in inactive bent conformation
* ATP phsophorylation by MLCK causes active state
* activate state is extended and allows formation of bipolar myosin thick filaments
87
filopodia are
| structure
bundles of parallel actin filaments
88
Lamellipodia are
| structure
sheets of cross linked actin filaments
89
invadopodia secret
matrix degrading proteases
90
_ are used to study lemellipodia
keratocytes
91
actin polymerization occurs at the
leading edge
92
newly formed filaments at the leading edge contain mostly _ while the rear end contains _
ATP- actin, ADP-actin
93
cofilin
preferentially binds to filaments containing ADP-actin, deplymerizing the actin filaments at the rear of the network
94
what does actin networks rely on to move forward
treadmilling
95
focal contacts serve as _, allowing
anchors for the leading edge, allowing the cell ot generate traction on the substratum and move forward
96
focal adhesions are formed
between actin skeleton and components of the ECM
97
activation of Cdc42
triggers actin polymerization and bundling to form filopodia
98
activation of Rac
promotes actin polymerization at the cell periphery, leading to lamellipodia
99
activation of Rho triggers
formation of stress fibers and the clustering of integrins and associated proteins to form adhesions
100
how does Cdc42 work
Cdc42-GTP binds to open, active form of WASp, active WASp bind to Arp 2/3 and increase its nucleating activity
101
Rac-GTP activates
WASp and PAK which leads to brached actin web in lamellipodia
102
Rac-GTP inhibits
MLCK and MHC which causes less stress fiber formation
103
PAK inhibits
MHC and MLCK which decreases myosin activity and less stress fiber formation
104
Rho--GTP pathway
* activates formins -> actin bundle growth
* activates Rock which activates MLC(P) and LIM and inhibits MLC phosphatase
* MLC(P) increases myosin activity
* LIM inhibits cofilin
* overall everything leads to more stress fibers and integrin clustering and focal adhesion formation
105
binding of a chemoattractant leads to the
activation of Rac at the leading edge and Rho at the trailing edge
106
Rho and Rac activation
inhibites each other
107
Intermediate Filaments are most prominent
in cells subjected to mechanical stress
| ropelike -> good for stretch but dont break
107
Intermediate Filaments are most prominent
in cells subjected to mechanical stress
| ropelike -> good for stretch but dont break
108
IF main function is to
enable cells to withstand stretching
109
IL monomers are
long fibrous proteins which form coiled coil dimers
110
IF monomers are _
| structure
alpha helical rods with heptad repeats
111
why are coiled coils of IF so stable
monomers have 7 repeats in which first and fourth AA are nonpolar
* non polar stripes align and form hydrophobic interactions between two alpha helix monomers, polar side chains exposed
112
soluable subunits of IF
* tetramers
* two dimers align side by side in an antiparllel straggered formation to form non po;ar tetramers
* tetramers interaction end to end to form protofilament
113
IFs are formed from
8 protofilaments packed together and twisted around each other
114
cross sections of IFs contain
8 tratramers, 16 dimers and 32 alpha helices
115
IF are non polarized bc
half of the dimers point in opposite directions
116
strength of IFs comes from
lateral, hydrophobic interactions between protofilaments
117
keratin filaments are bundles by proteins to form
apical layer of epidermis
118
mutations in keratin cause
skin blistering diseases
119
neurofilaments are a type of
IFs
120
desmin is a type of
IF expressed in muscle cells
121
desmin is a type of
IF expressed in muscle cells
122
desmin forms
a scaffold around the Z disc of the sarcomere
123
nuclear lamins
forms a 2d network which gives nucleus shape and stability
124
nculear lamins provide
anchoring sites for chromatin and nuclear pores
125
A-type lamins finction
as scaffolds for proteins that control transcription, chromatin organization and signal transduction
126
laminopathies are associated with _ and are due to _
mutations in lamin A and may be due to weakening of the nuclear envelope
| cause premature aging
127
laminopathies are associated with _ and are due to _
mutations in lamin A and may be due to weakening of the nuclear envelope
| cause premature aging
128
plakins
link IF networks to the rest of the cytoskeleton
129
SUN proteins bind
nuclear lamina or chromosomes
| located in inner nuclear membrane
130
located in outer nuclear membrane KASH proteins bind
actin filaments, microtubles and IFs
131
in the perinuclear space,
SUN proteins bind to KASH proteins, thus linking the nucleus to the cytoskeleton
132
cytoskeleton being linked ot nuclear interior is important for
movement of chromosomes
133
during muscle contraction, the A band
styas constant
134
during muscle contraction, the I band
moves towards the center of the sarcomere and increases its overlap and decreases in length
135
during muscle contraction, the H band
H band becomes shorter in length as its overlap with other components increases.
136
during muscle contraction, the Z discs
come closer together
137
during muscle contraction, the M line
remains in the center
138
during muscle contraction, the M line
remains in the center
139
during muscle contraction, titan
is stretched
140
Why is it important for Rac to be activated at the leading edge, and Rho at the trailing edge?
* Rac responsible for protusion and attachement
* Rac results in lamellipodia which importnat for protrusion
* Rho required for traction because stress fiber formation
141
Proteins which bind to actin subunits and prevent their incorporation into filaments.
thymosin
142
Membrane folds which convey electrical signals to the myofibrils of muscle cells.
t tubules
143
Membrane folds which convey electrical signals to the myofibrils of muscle cells.
t tubules
144
The cytoskeletal filament that is not polarized.
intermediate
145
Gel-forming protein which cross-links actin filaments at right angles to promote the formation of web-like networks with the consistency of highly viscous gels.
filamen
146
The class of intermediate filaments expressed in epithelial cells.
keratins
147
Formins promote
the formation of unbranched actin filaments.
148
Region of the sarcomere where the plus ends of thin filaments are capped by CapZ and bundled by α-actinin.
z disc
149
Flat, sheet-like protrusions formed by actin networks at the leading edge of migrating cells.
lamellipodia
150
Monomeric GTPase which promotes the formation of stress fibers via the activation of formin proteins and myosin-II filament assembly.
rho-GTP
151
chemotaxis
Movement of a cell in the direction of a diffusible chemical gradient.
152
The _ surface of skin, known as the stratum corneum, is composed of the...
apical, remnants of dead skin cells and the network of filaggrin-bundled keratin filaments that were contained within those cells.
153
S1 fragments are
myosin motor domains isolated by the enzymatic digestion of thick filaments.
