Microfilaments

Question 1

components of the cytoskeleton

Answer 1

microfilaments, intermediate filaments, microtubules

Question 2

microfilament

Answer 2

smallest component of cytoskeleton; dynamic structure involved in movement

Question 3

intermediate filament

Answer 3

midsized component, static structure involved in stabilization

Question 4

microtubules

Answer 4

largest component, dynamic structure involved in movement

Question 5

epithelial cell polarity

Answer 5

apical domain w/ microvilli and cell junctions; basolateral domain with cortical band & attached to basal lamina

Question 6

motile cell polarity

Answer 6

leading edge w/ filopodium; lagging edge

Question 7

cellular structures containing actin

Answer 7

microvilli, cell cortex, circumferential belt, leading edge, filopodia, contractile ring, stress fibers

Question 8

types of actins

Answer 8

α actin, ß actin, gamma actin

Question 9

α actin

Answer 9

involved in muscle contraction (circus. belt and contractile ring)

Question 10

ß actin

Answer 10

part of the leading edge/lamellipodium

Question 11

gamma actin

Answer 11

makes up stress fibers

Question 12

4 states of actin

Answer 12

G-Actin ATP, G-Actin ADP, F-Actin ATP, F-Actin ADP

Question 13

most common states of actin

Answer 13

G-Actin ATP and F-Actin ADP

Question 14

actin polymerization

Answer 14

nucleation, elongation, steady state

Question 15

How do the plus and minus ends of microfilaments differ?

Answer 15

ATP binding site of a G-Actin align to the - end of the filament; Monomers add preferentially to the + end of the microfilament.

Question 16

critical concentration

Answer 16

Concentrations of monomers needed to add to the +/- end of the microfilament; Higher conc. needed to add to - end of microfilament.

Question 17

treadmilling

Answer 17

Monomers add preferentially to one end and dissociate at the other.
Accelerated by profilin and cofilin.

Question 18

Cofilin

Answer 18

severing factor

Question 19

Profilin

Answer 19

exchange factor; removes ADP and adds ATP to encourage polymerization

Question 20

Thymosin ß4

Answer 20

provides a reservoir of ATP G-actin by binding and preventing its addition to the microfilament

Question 21

CapZ

Answer 21

binds + end of microfilament to prevent subunit addition/loss

Question 22

Tropomodulin

Answer 22

binds - end of microfilament to prevent subunit addition/loss

Question 23

Formins

Answer 23

create a dimer at the end of the filament and guides the addition of G-actin to prevent branching

Question 24

Arp 2/3

Answer 24

(protein machine) binds to the side of the actin filament and binds a new nucleus to form branch at 70 degree angle

Question 25

regulatory proteins

Answer 25

profilin, thymosin ß4, cofilin

Question 26

capping molecules

Answer 26

capZ, tropomodulin

Question 27

molecules influencing microfilament structure

Answer 27

formins, arp2/3

Question 28

How do actin cross linking proteins stabilize actin structures?

Answer 28

They have 2 actin binding domains that bind to the microfilament and stabilize in various arrangements. The type of cross linking depends on the distance between the actin binding domains.

Question 29

actin crosslinking proteins

Answer 29

fimbrin, α actinin, spectrin, filamin

Question 30

fimbrin

Answer 30

2 actin binding domains with short tail; stabilizes microvilli, filopodia, and focal adhesions

Question 31

α actinin

Answer 31

actin binding domain with short tail, arranged head to tail; stabilizes stress fibers, filopodia, & muscle Z band

Question 32

spectrin

Answer 32

actin binding domain with longer tail, arranged head to tail; stabilizes cell cortex

Question 33

filamin

Answer 33

actin binding domain with medium tail, connected at the tail end; stabilizes leading edge, stress fibers, and filopodia

Question 34

myosin structure

Answer 34

globular (ATP binding) head, long coiled tail, flexible neck; myosin I is a monomer, others are dimers

Question 35

How does myosin II move actin filaments?

Answer 35

Binds ATP, head released from actin. Hydrolysis of ATP to ADP + P, myosin head rotates into "cocked" state. Myosin head binds actin filament. "Power stroke" - release of P and elastic energy straightens myosin & moves actin filament toward (-) end. ADP released; ATP bound; head released from actin

Question 36

How does myosin V move vesicles?

Answer 36

Binds microfilament with head. | Tail interacts with receptor or molecule in the membrane of a vesicle/organelle.

Question 37

directional movement of myosin

Answer 37

all myosin EXCEPT myosin VI move toward the positive end

Question 38

actin-containing contractile structures in nonmuscle cells

Answer 38

polarized epithelial cells: circumferential belt (structural) motile cells: stress fibers, focal adhesions w/ integrins cleavage furrow: contractile ring

Question 39

describe how cells move

Answer 39

Extension - sensing the environment and reaching out with the leading edge (signalling activates Cdc42 and Rac). Adhesion - formation of new focal adhesion (integrin binds to ECM and interacts with internal microfilaments); gives leverage to start moving forward. Translocation - nucleus will orient near front of the cell; mass of the cell will move forward toward leading edge as actin filaments rearrange. De-adhesion - rear focal adhesion releases to allow cell to propel forward (in some cells, Rho promotes de-adhesion).

Question 40

members of the Rho family of GTPases

Answer 40

Rho, Rac, and Cdc42

Question 41

Rho

Answer 41

found in stress fibers; activates actin and myosin activity

Question 42

Rac

Answer 42

found in the lamellipodia; activates WAVE > Arp 2/3

Question 43

Cdc42

Answer 43

found in filopodia; activates WASP > Arp2/3 and sets polarity

Question 44

How do intermediate filaments differ from microfilaments and microtubules?

Answer 44

do not hydrolyze ATP or GTP, more rigid, rod-like structure, made of lamins and keratins

Question 45

lamins

Answer 45

give nuclear structure and strength (found in all cells but red blood cells)

Question 46

keratins

Answer 46

found outside of the nucleus; give structure to cell and the placement of the nucleus