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Cellular and Molecular Biology > Final: Ch 17 Actin > Flashcards

Final: Ch 17 Actin Flashcards

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1
Q

microvilli

A

fingerlike projections that increase the area of the plasma membrane available for nutrient absorption

non-motile, made of actin

lining of digestive system

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2
Q

is the internal motile machinery of macrophages and other crawling cells always oriented int he direction they crawl?

A

yes

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3
Q

cell polarity

A

the ability of cells to generate functionally distinct regions

ex. cell division

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4
Q

cytoskeleton

A

a 3D filamentous protein network found in all eukaryotes

gives a cell shape, organization, and polarity

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5
Q

the cytoskeleton is composed of _ major filament systems

A

3

microfilaments, microtubules, intermediate filaments

the monomers undergo assembly and disassembly, allowing the cell to assemble or disassemble structures

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6
Q

microfilaments

A

polymers of the protein actin

can function on their own or serve as tracks for ATP powered myosin motor proteins

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7
Q

microfilaments are especially important in the….

A

organization of the cell membrane

gives shape to surface structures like microvilli

cell division

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8
Q

myosin motor proteins

A

provide a contractile function (like in muscle)

ferry cargo along microfilaments

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9
Q

microtubules

A

long tubes made of the protein tubulin

movement within the cell

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10
Q

function of microtubules

A

organizational framework for organelles

structural support for cilia and flagella

mitotic spindle

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11
Q

kinesins and dyneins

A

molecular motors that transport cargo along microtubules

powered by ATP hydrolysis

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12
Q

intermediate filaments

A

tissue specific filamentous structures

less dynamic, more structural

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13
Q

functions of intermediate filaments

A

structural support to nuclear membrane

structural integrity to cells in tissues

structural and barrier functions in skin, hair, and nails

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14
Q

to establish arrangements of the cytoskeleton, cells must sense ______, and interpret them

A

signals – cell-surface receptors detect and activate signal-transduction pathways

soluble factors bathing the cell

adjacent cells

ECM

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15
Q

how does cell motility work (microfilaments)

A

polymerization at the front of the cell

contractions at the back of the cell

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16
Q

macrophage (WBC) motility

A

move out of blood vessels and crawl through tissues to sites of infection

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17
Q

neural crest cell motility in embryos

A

from dorsal midline to development of the face

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18
Q

cell motility in neurons

A

growth cones at the ends of axons and dendrites move outward

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19
Q

chemotaxis definition

A

moving in response to external signals

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20
Q

microfilaments can assemble into a wide variety of _______ within a cell

A

structures

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21
Q

cell cortex

A

a less ordered network of microfilaments under the plasma membrane

support and organization

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22
Q

adherens belt

A

a contractile band on the outside of epithelial cells to form a seal between cells

made of microfilaments

associated with adherens junctions to provide strength

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23
Q

lamellipodium/leading edge

A

a network of microfilaments found in migrating cells at the front of the cell

may also have protruding bundles of microfilaments called filopodia

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24
Q

stress fiber

A

contractile microfilaments attached to the external substratum via focal adhesions/contacts

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25
macrophages use __________ ___________ during phagocytosis to engulf and internalize pathogens
contractile microfilaments
26
short bursts of ____ ________ assembly can power the movement of endocytic vesicles away from the plasma membrane
actin filament assembly
27
contractile ring
polymer of actin and non-muscle myosin connected to cell membrane constricts to form 2 daughter cells in the process of cytokinesis (late cell division)
28
actin
basic building block of microfilaments a protein that can reversibly assemble into a polarized filament with functionally different ends
29
actin-binding protein
assembles actin into various structures
30
what does the name microfilament mean
actin in its polymerized form with associated proteins
31
actin is _____, ______, and highly _______
ancient, abundant, highly conserved multiple actin genes in eukaryotes are related to a bacterial gene that evolved to have a role in bacterial cell-wall synthesis
32
_ types of actin isoform
3 alpha-actin beta-actin gamma-actin
33
what functions are associated with the 3 isoforms of actin
alpha-actin: contractile structures beta-actin: cell cortex and leading edge of motile cells gamma-actin: filaments in stress fibers
34
_-actin monomers assemble into long, helical _-actin polymers
G-actin, F-actin
35
G-actin
globular monomer
36
F-actin
filamentous polymer made of G-actin monomers
37
each actin molecule contains...
a Mg ion complexes with either ATP or ADP
38
the G-actin monomer is separated into to lobes by a deep ____
cleft base of the cleft contains the ATPase fold (Mg and ATP are bound here) floor of the cleft is a hinge
39
adding cations of a solution of G-actin does what
causes it to polymerize into F-actin filaments reversible (when concentration of ions is lowered)
40
F-actin has ______ and _______ polarity
structural, functional
41
all subunits in an actin filament are oriented....
the same way
42
polarity of an actin filament
one end differs from the other ( + ) end gets actin monomers added (grows) ( - ) end has actin monomers removed (loses)
43
what can be added to the ends of actin filaments to stabilize?
CAP proteins ex. actin in striated muscle (no treadmilling)
44
does addition of actin happen faster in the front or the back?
front ( + ) end
45
polymerization of G-actin to F-actin requires what
energy ATP --> ADP
46
myosin binds specifically to...
actin filaments
47
myosin S1
the actin-binding head domain of myosin
48
decorating experiment (w/ electron micrograph)
an excess of myosin S1 (binds actin heads) is mixed with actin filaments when all the actin subunits are bound by myosin, the filament appears "decorated" with arrowheads that all point toward one end of the filament
49
what have decorating experiments allowed researchers to determine
the polarity of actin filaments in vitro and in cells the arrowhead points to the ( - ) end (pointed end) the ( + ) end is known as the barbed end
50
actin polymerization takes _ steps
3 nucleation, elongation, steady-state
51
nucleation phase
a lag period where G-actin subunits combine into 2-3 subunits when the oligomer reaches 3 subunits it acts as a nucleus for the elongation phase
52
elongation phase
short actin oligomer adds actin monomers to both ends as F-actin filaments grow, the concentration of G-actin monomers decreases until equilibrium is reached
53
steady-state phase
G-actin monomers exchange with subunits at the F-actin filament ends no net change in filament length
54
critical concentation Cc
the concentration at which filaments are formed (must be higher)
55
the rate of addition of ATP-G-actin is nearly __ times faster at which end of the filament?
10 times faster at the + end
56
what is the rate of addition of ATP-G-actin dependent on?
the concentration of free ATP-G-actin
57
is the rate of subunit loss from each end similar?
yes not dependent on the free ATP-G-actin concreation
58
is there a lower critical concentration at the + end? what does this mean
yes, means that rate of addition of ATP-G-actin to + end is faster
59
treadmilling (steady-state)
polymer is in dynamic equilibrium where it is being polymerized and depolymerized at the same time ATP-actin is being added faster at the + end than - end, and ADP-actin is being removed from the - end -- hence treadmilling
60
is their treadmilling in muscle fiber?
no
61
what is the ability of actin filaments to treadmill driven by?
ATP hydrolysis as ATP-actin is bound to + end, ATP-actin is hydrolyzed to ADP-Pi-actin at the - end (Pi gets released)
62
actin-filament treadmilling is accelerated by ______ and _______
profilin and cofilin
63
what does profilin do
a small protein that binds ADP-actin on the opposite side of the nucleotide binding cleft when it binds ADP-actin, the cleft opens and enhances the loss of ADP, which is replaced by ATP profilin-ATP-actin binds + end, and profilin dissociates
64
what does cofilin do
small protein that binds F-actin-ADP subunits near - end bridges two actin monomers and twists the filament to break it into small pieces released ADP-actin is recharged to profilin and added to the + end
65
what regulates profilin and cofilin
signal transduction pathways
66
thymosin beta-4
an actin monomer sequestering protein that binds ATP-G-actin inhibits ATP-G-actin's addition to the filament provides a reservoir of actin for polymerization
67
capping proteins do what
block assembly and disassembly at both ends of the actin filament CapZ binds + end tropomodulin binds - end
68
where is tropomodulin found
in cells where actin filaments need to be highly stabilized ex. RBC, muscle
69
gelsolin
a cap protein ( + ) end that can sever the filament regulated by increasing levels of Ca
70
2 examples of a actin nucleating proteins
Arp2/3 and formins nucleate actin assembly via signal transduction pathways
71
integrin
cell surface transmembrane protein that binds specifically to the ECM
72
how do integrins work
hold onto the cell but lets go at the back, like tracks on a tank forward motion comes from the back -- like squeezing toothpaste
73
are integrins recycled?
yes, to the front by endocytosis microtubules and motor proteins move the integrin vesicles to the front
74
actin is depolymerized by
cutting the polymer

Cellular and Molecular Biology (34 decks)

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