Final: Ch 17 Actin Flashcards Preview

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

Flashcards in Final: Ch 17 Actin Deck (74):
1

microvilli

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

non-motile, made of actin

lining of digestive system

2

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

yes

3

cell polarity

the ability of cells to generate functionally distinct regions

ex. cell division

4

cytoskeleton

a 3D filamentous protein network found in all eukaryotes

gives a cell shape, organization, and polarity

5

the cytoskeleton is composed of _ major filament systems

3

microfilaments, microtubules, intermediate filaments

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

6

microfilaments

polymers of the protein actin

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

7

microfilaments are especially important in the....

organization of the cell membrane

gives shape to surface structures like microvilli

cell division

8

myosin motor proteins

provide a contractile function (like in muscle)

ferry cargo along microfilaments

9

microtubules

long tubes made of the protein tubulin

movement within the cell

10

function of microtubules

organizational framework for organelles

structural support for cilia and flagella

mitotic spindle

11

kinesins and dyneins

molecular motors that transport cargo along microtubules

powered by ATP hydrolysis

12

intermediate filaments

tissue specific filamentous structures

less dynamic, more structural

13

functions of intermediate filaments

structural support to nuclear membrane

structural integrity to cells in tissues

structural and barrier functions in skin, hair, and nails

14

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

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

soluble factors bathing the cell

adjacent cells

ECM

15

how does cell motility work (microfilaments)

polymerization at the front of the cell

contractions at the back of the cell

16

macrophage (WBC) motility

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

17

neural crest cell motility in embryos

from dorsal midline to development of the face

18

cell motility in neurons

growth cones at the ends of axons and dendrites move outward

19

chemotaxis definition

moving in response to external signals

20

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

structures

21

cell cortex

a less ordered network of microfilaments under the plasma membrane

support and organization

22

adherens belt

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

23

lamellipodium/leading edge

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

may also have protruding bundles of microfilaments called filopodia

24

stress fiber

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

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