Lecture 16 - Cytoskeleton & CM: Microfilaments

Question 1

microfilaments are the _______ of the cytoskeletal filaments

Answer 1

smallest

Question 2

what roles to microfilaments play?

Answer 2

• muscle contraction
• cell migration
• amoeboid movement
• cytoplasmic streaming

Question 3

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

Answer 3

actin

Question 4

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

Answer 4

alpha, beta and gamma

Question 5

what happens to actin once its been synthesized?

Answer 5

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

Question 6

G-actin polymerize to form __________

Answer 6

microfilaments = F-actin

Question 7

microfilaments hydrolyze ____ while microtubules hydrolyze ____

Answer 7

ATP, GTP

Question 8

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

Answer 8

true

Question 9

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

Answer 9

F-actin

Question 10

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

Answer 10

true

Question 11

where are microfilaments concentrated?

Answer 11

beneath the plasma membrane

Question 12

the polarity of microfilaments is reflected in the….

Answer 12

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

Question 13

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

Answer 13

slowly hydrolyzed, hydrolysis is not required for polymerization

Question 14

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

Answer 14

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

Question 15

cells that crawl have _______ and _______ at their leading edge

Answer 15

lamellipodia and filopodia

Question 16

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

Answer 16

stress fibers

Question 17

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

Answer 17

actin-binding proteins

Question 18

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

Answer 18

thymosin beta-4

Question 19

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

Answer 19

profilin

Question 20

def: filament-severing protein, that facilitates depolymerization

Answer 20

cofilin

Question 21

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

Answer 21

capping proteins

Question 22

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

Answer 22

CapZ

Question 23

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

Answer 23

tropomodulins

Question 24

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

Answer 24

Gelsolin

Question 25

_______ control the assembly of actin filaments in vivo

Answer 25

formins

Question 26

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

Answer 26

formins

Question 27

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

Answer 27

(+)

Question 28

def: act to join two microfilaments together where they intersect

Answer 28

filamin

Question 29

def: formed by actin when bundled in tightly organized arrays

Answer 29

focal contacts or focal adhesions

Question 30

def: bundles microfilaments in microvilli

Answer 30

fimbrin

Question 31

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

Answer 31

peripheral membrane proteins

Question 32

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

Answer 32

spectrin and ankyrin

Question 33

what is the slowest step in the microfilament formation

Answer 33

nucleation

Question 34

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

Answer 34

Arp2/3 complex

Question 35

what does Arp2/3?

Answer 35

creates a template to which actin monomers can be added

Question 36

actin can form a ______ _____ network prominent in Lamellipodia

Answer 36

tree-like

Question 37

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

Answer 37

intermediate filaments

Question 38

what is an abundant intermediate filament?

Answer 38

keratin

Question 39

what do intermediate filaments do?

Answer 39

support the cytoskeleton by acting as a scaffold

Question 40

what is different about intermediate filaments?

Answer 40

they are fibrous rather than globular

Question 41

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

Answer 41

intermediate filaments assembling to form fibrous subunits

Question 42

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

Answer 42

N-terminal and C-terminal

Question 43

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

Answer 43

globular

Question 44

what happens when two fibrous polypeptides spontaneously interact?

Answer 44

- 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

Question 45

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

Answer 45

eight

Question 46

where are units of the IF removed from?

Answer 46

the interior rather than the ends

Question 47

does IF assembly require energy?

Answer 47

no

Question 48

microtubules __________ _________ when a cell is compressed

Answer 48

resist bending

Question 49

microfilaments serve as contractile elements that ____________ __________

Answer 49

generate tension

Question 50

intermediate filaments are elastic and can ________________ _____________ __________

Answer 50

withstand tensile forces

Question 51

are intermediate filaments static structures that can be dynamically remodelled?

Answer 51

yes

Question 52

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

Answer 52

nuclear matrix

Question 53

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

Answer 53

nuclear lamina

Question 54

what is the nuclear lamina composed of?

Answer 54

intermediate filaments composed of lamins

Question 55

kinesin is an_________ MT motor

Answer 55

anterograde

Question 56

dynein is an _________ MT motor

Answer 56

retrograde