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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
Q

macrophages use __________ ___________ during phagocytosis to engulf and internalize pathogens

A

contractile microfilaments

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26
Q

short bursts of ____ ________ assembly can power the movement of endocytic vesicles away from the plasma membrane

A

actin filament assembly

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27
Q

contractile ring

A

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)

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28
Q

actin

A

basic building block of microfilaments

a protein that can reversibly assemble into a polarized filament with functionally different ends

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29
Q

actin-binding protein

A

assembles actin into various structures

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30
Q

what does the name microfilament mean

A

actin in its polymerized form with associated proteins

31
Q

actin is _____, ______, and highly _______

A

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
Q

_ types of actin isoform

A

3

alpha-actin

beta-actin

gamma-actin

33
Q

what functions are associated with the 3 isoforms of actin

A

alpha-actin: contractile structures

beta-actin: cell cortex and leading edge of motile cells

gamma-actin: filaments in stress fibers

34
Q

_-actin monomers assemble into long, helical _-actin polymers

A

G-actin, F-actin

35
Q

G-actin

A

globular monomer

36
Q

F-actin

A

filamentous polymer made of G-actin monomers

37
Q

each actin molecule contains…

A

a Mg ion complexes with either ATP or ADP

38
Q

the G-actin monomer is separated into to lobes by a deep ____

A

cleft

base of the cleft contains the ATPase fold (Mg and ATP are bound here)

floor of the cleft is a hinge

39
Q

adding cations of a solution of G-actin does what

A

causes it to polymerize into F-actin filaments

reversible (when concentration of ions is lowered)

40
Q

F-actin has ______ and _______ polarity

A

structural, functional

41
Q

all subunits in an actin filament are oriented….

A

the same way

42
Q

polarity of an actin filament

A

one end differs from the other

( + ) end gets actin monomers added (grows)

( - ) end has actin monomers removed (loses)

43
Q

what can be added to the ends of actin filaments to stabilize?

A

CAP proteins

ex. actin in striated muscle (no treadmilling)

44
Q

does addition of actin happen faster in the front or the back?

A

front ( + ) end

45
Q

polymerization of G-actin to F-actin requires what

A

energy

ATP –> ADP

46
Q

myosin binds specifically to…

A

actin filaments

47
Q

myosin S1

A

the actin-binding head domain of myosin

48
Q

decorating experiment (w/ electron micrograph)

A

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
Q

what have decorating experiments allowed researchers to determine

A

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
Q

actin polymerization takes _ steps

A

3

nucleation, elongation, steady-state

51
Q

nucleation phase

A

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
Q

elongation phase

A

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
Q

steady-state phase

A

G-actin monomers exchange with subunits at the F-actin filament ends

no net change in filament length

54
Q

critical concentation Cc

A

the concentration at which filaments are formed (must be higher)

55
Q

the rate of addition of ATP-G-actin is nearly __ times faster at which end of the filament?

A

10 times faster at the + end

56
Q

what is the rate of addition of ATP-G-actin dependent on?

A

the concentration of free ATP-G-actin

57
Q

is the rate of subunit loss from each end similar?

A

yes

not dependent on the free ATP-G-actin concreation

58
Q

is there a lower critical concentration at the + end? what does this mean

A

yes, means that rate of addition of ATP-G-actin to + end is faster

59
Q

treadmilling (steady-state)

A

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
Q

is their treadmilling in muscle fiber?

A

no

61
Q

what is the ability of actin filaments to treadmill driven by?

A

ATP hydrolysis

as ATP-actin is bound to + end, ATP-actin is hydrolyzed to ADP-Pi-actin at the - end (Pi gets released)

62
Q

actin-filament treadmilling is accelerated by ______ and _______

A

profilin and cofilin

63
Q

what does profilin do

A

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
Q

what does cofilin do

A

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
Q

what regulates profilin and cofilin

A

signal transduction pathways

66
Q

thymosin beta-4

A

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
Q

capping proteins do what

A

block assembly and disassembly at both ends of the actin filament

CapZ binds + end

tropomodulin binds - end

68
Q

where is tropomodulin found

A

in cells where actin filaments need to be highly stabilized

ex. RBC, muscle

69
Q

gelsolin

A

a cap protein ( + ) end that can sever the filament

regulated by increasing levels of Ca

70
Q

2 examples of a actin nucleating proteins

A

Arp2/3 and formins

nucleate actin assembly via signal transduction pathways

71
Q

integrin

A

cell surface transmembrane protein that binds specifically to the ECM

72
Q

how do integrins work

A

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
Q

are integrins recycled?

A

yes, to the front by endocytosis

microtubules and motor proteins move the integrin vesicles to the front

74
Q

actin is depolymerized by

A

cutting the polymer

Cellular and Molecular Biology (34 decks)

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