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MBB 231 > Lecture 16 - Cytoskeleton & CM: Microfilaments > Flashcards

Lecture 16 - Cytoskeleton & CM: Microfilaments Flashcards

1
Q

microfilaments are the _______ of the cytoskeletal filaments

A

smallest

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2
Q

what roles to microfilaments play?

A
  • muscle contraction
  • cell migration
  • amoeboid movement
  • cytoplasmic streaming
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3
Q

def: highly conserved globular protein, can be divided into muscle-specific or non-muscle streams

A

actin

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4
Q

muscle-specific actins are ___ actins and non-muscle specific actins are ____ and ____ actins

A

alpha, beta and gamma

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5
Q

what happens to actin once its been synthesized?

A

folds into globular U-shaped molecule that can bind to ATP and ADP

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6
Q

G-actin polymerize to form __________

A

microfilaments = F-actin

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7
Q

microfilaments hydrolyze ____ while microtubules hydrolyze ____

A

ATP, GTP

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8
Q

T or F: G-actin can polymerize reversibly into filaments with a lag phase and elongation phase

A

true

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9
Q

def: composed of two linear strands go polymerized G-actin, wound into a helix

A

F-actin

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10
Q

T or F: all the actin monomers in the filament have the same orientation

A

true

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11
Q

where are microfilaments concentrated?

A

beneath the plasma membrane

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12
Q

the polarity of microfilaments is reflected in the….

A

more rapid addition of G-actin at the (+) end than the (-) end

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13
Q

after G-actin monomers assemble onto a microfilament, the ATP bound to them is _____ _______

A

slowly hydrolyzed, hydrolysis is not required for polymerization

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14
Q

what do the growing ends of the microfilament have on them vs. the rest of the microfilament

A

growing ends have ATP-actin, rest has ADP-actin

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15
Q

cells that crawl have _______ and _______ at their leading edge

A

lamellipodia and filopodia

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16
Q

cells that adhere tightly to the underlying substratum have organized bundles called _____ _____

A

stress fibers

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17
Q

def: organization and behaviour of microfilaments inside a cell are regulated by these

A

actin-binding proteins

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18
Q

def: binds to ATP-actin monomers and prevents them from polymerizing

A

thymosin beta-4

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19
Q

def: binds to ADP-G-actin and catalyzes the exchange of ADP for ATP, promoting polymerization

A

profilin

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20
Q

def: filament-severing protein, that facilitates depolymerization

A

cofilin

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21
Q

def: bind the ends of a filament, to prevent further loss or addition of subunits, this can stabilize microfilaments

A

capping proteins

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22
Q

def: binds to (+) ends to prevent addition of subunits there

A

CapZ

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23
Q

def: bind to (-) ends, preventing loss of subunits there

A

tropomodulins

24
Q

def: breaks actin MFs and caps the newly exposed (+) ends, preventing further polymerization

A

Gelsolin

25
Q

_______ control the assembly of actin filaments in vivo

A

formins

26
Q

def: large multi-domain proteins that directly nucleate polymerization of unbranched actin filaments

A

formins

27
Q

the formins remain associated with the fast growing ___ end, enabling rapid insertion of actin subunits while protecting the end from capping proteins

A

(+)

28
Q

def: act to join two microfilaments together where they intersect

A

filamin

29
Q

def: formed by actin when bundled in tightly organized arrays

A

focal contacts or focal adhesions

30
Q

def: bundles microfilaments in microvilli

A

fimbrin

31
Q

indirect connections to the membrane requires one or more ________ __________ _________

A

peripheral membrane proteins

32
Q

an example of microfilament to membrane linkage is through _______ and _________

A

spectrin and ankyrin

33
Q

what is the slowest step in the microfilament formation

A

nucleation

34
Q

when activated by WASP, the ______ ________ nucleates new branches on the sides of MF

A

Arp2/3 complex

35
Q

what does Arp2/3?

A

creates a template to which actin monomers can be added

36
Q

actin can form a ______ _____ network prominent in Lamellipodia

A

tree-like

37
Q

which cytoskeletal component is the most stable, the least soluble, and are not polarized?

A

intermediate filaments

38
Q

what is an abundant intermediate filament?

A

keratin

39
Q

what do intermediate filaments do?

A

support the cytoskeleton by acting as a scaffold

40
Q

what is different about intermediate filaments?

A

they are fibrous rather than globular

41
Q

def: all have a central rod-shaped alpha helix domain that is conserved in size, secondary structure, and to some extent, in sequence

A

intermediate filaments assembling to form fibrous subunits

42
Q

flanking the central helical domain are __-_________ and __-_________ domains that differ greatly among intermediate filaments proteins

A

N-terminal and C-terminal

43
Q

IF proteins are primarily fibrous molecules, with a _________ domain on each end

A

globular

44
Q

what happens when two fibrous polypeptides spontaneously interact?

A
  • wrap around each other creating a 45 nm rope-like dimer
  • the two dimers assemble together in a staggered C- to N-terminal orientation creating an anti-parallel tetramer with no polarity
45
Q

________ tetramers pack laterally together to for a filament that is one “unit” long

A

eight

46
Q

where are units of the IF removed from?

A

the interior rather than the ends

47
Q

does IF assembly require energy?

A

no

48
Q

microtubules __________ _________ when a cell is compressed

A

resist bending

49
Q

microfilaments serve as contractile elements that ____________ __________

A

generate tension

50
Q

intermediate filaments are elastic and can ________________ _____________ __________

A

withstand tensile forces

51
Q

are intermediate filaments static structures that can be dynamically remodelled?

A

yes

52
Q

def: insoluble fibrous network that helps maintain the shape of the nucleus and serves as attachment site for chromatin

A

nuclear matrix

53
Q

def: thin dense meshwork of fibres lining the inner surface of the inner nuclear membrane

A

nuclear lamina

54
Q

what is the nuclear lamina composed of?

A

intermediate filaments composed of lamins

55
Q

kinesin is an_________ MT motor

A

anterograde

56
Q

dynein is an _________ MT motor

A

retrograde

MBB 231 (19 decks)

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