Lecture 6

Question 1

List the 3 types of cytoskeleton components and their thickness

Answer 1

Microfilaments (actin) (7nm thick) Intermediate Filaments (8-10nm thick) Microtubules (25 nm in diameter)

Question 2

Describe actin monomers

Answer 2

known as G-actin Has an ATP binding site Displays polarity (faces the same direction) when polymerized with other G-actin

Question 3

Describe active filaments

Answer 3

long chains known as F-actin Organized into bundles and 3D networks

Question 4

describe the structure of actin microfilaments

Answer 4

consist of a double helical chain of G-actin subunits

Question 5

Describe the process of actin polymerization

Answer 5

ATP actin associates with the barbed (plus) end of actin and is then hydrolyzed to ADP after polymerization Monomers may bind to either end, but bind much faster to the barbed end

Question 6

Define treadmilling

Answer 6

occurs when intermediate concentrations of G-actin favor a dynamic addition of monomers to the plus end, while monomers fall off of the pointed end

Question 7

(Drugs that affect polymerization) Define Cytochlasins

Answer 7

bind to barbed ends of actin and block elongation This inhibits cellular movement, such as cell division

Question 8

(Drugs that affect polymerization) Define Phalloidin

Answer 8

binds to actin filaments and prevents dissociation into monomers ○ Can be labeled with fluorescent dyes to visualize actin filaments

Question 9

(actin binding molecules) define Spectrin

Answer 9

binds the cortical cytoskeleton to the plasma membrane Found in RBC’s

Question 10

(actin binding molecules) define Dystrophin

Answer 10

Binds the cortical cytoskeleton to the plasma membrane

Question 11

(actin binding molecules) define Villin and Fimbrin

Answer 11

Cross-links in microvilli

Question 12

(actin binding molecules) define Calmodulin and Myosin I

Answer 12

cross-links plasma membrane in microvilli

Question 13

(actin binding molecules) define Alpha-actinin

Answer 13

Cross-links stress fibers and connects actin to protein-plasma membrane

Question 14

(actin binding molecules) define Filamin

Answer 14

Cross-links at wide angles to form screen-like gels

Question 15

(actin binding molecules that control treadmilling) define Thymosin

Answer 15

Captures actin monomers and prevents them from being polymerized

Question 16

(actin binding molecules that control treadmilling) define Profilin

Answer 16

regulates filament assemble by catalyzing the exchange of G-actin bound ADP for ATP This gets monomers ready to be polymerized

Question 17

(actin binding molecules that control treadmilling) define Gelsolin

Answer 17

cuts F-actin and adds a cap at the cut to prevent loss/addition of G-actin

Question 18

(actin binding molecules that control treadmilling) define Cofilin

Answer 18

triggers depolymerization of actin at the minus end

Question 19

(actin binding molecules that control treadmilling) define Arp 2/3

Answer 19

causes branching from the sides of the F-actin filament

Question 20

(actin binding molecules that control treadmilling) define Phalloidin

Answer 20

binds to actin filaments to prevent depolymerization

Question 21

(actin binding molecules that control treadmilling) define Latrunculins

Answer 21

Binds to G-actin and induces F-actin depolymerization

Question 22

Describe the structure of Intermediate filaments and differentiate it from microfilaments and microtubules.

Answer 22

Composed of 2 polypeptides, aligned tail to tail and head to head, and form a coiled dimer Dimers form tetramers in a staggered, antiparallel fashion (no distinct ends like actin) This makes them more stable and prevents treadmilling

Question 23

Describe the heirarchial structure intermediate filaments

Answer 23

2 monomers form a dimer 2 dimers form a tetramer tetramers form protofilaments 8 protofilaments form filaments

Question 24

describe the structure of a microtubule

Answer 24

Alpha and Beta units form Tubulin dimers (just the name of the bond) this forms microtubule protofilaments

Question 25

how are protofilaments arranged to form microtubules?

Answer 25

• Microtubules consist of 13 protofilaments arranged parallel in a hollow cylinder Protofilaments have a fast-growing plus end and a slow-growing minus end

Question 26

What is this

Answer 26

Microtubule

Question 27

List the 7 functions of the cytoskeleton

Answer 27

cell movement

Support and strenght for the cell

phagocytosis

mitotic spindel formation

cytokinesis

cell to cell and extracellular matrix adhesion

changes in cell shape

Question 28

Describe the role of microtubules in mitosis

Answer 28

form the mitotic center and mitotic spindle

MC: microtubule organizing center; centrioles; radiating microtubules

MS: kinetochore microdubules that are anchored at the centromeres (dynein/dynactin motor proteins walk on these)

polar microtubules which overlap with one another in the center of the cell and are not attached to chromosomes

Question 29

compare anterograde and retrograde transport

Answer 29

Anterograde transport: kinesin motor protein carries cargo along microtubules (minus to plus end; leaving)

Retrograde transport: transport of cargos along a microtubule that is mediated by cytoplasmic dynein (plus end to minus end; retuning)

Question 30

compare and contrast intraciliary transport and axonal transport

Answer 30

both use anterograde and retrograde transport

intracilliary transport involves the use of raft protein complexes in order to transport mulitple cargos at once

Question 31

what is the difference between myosin I and myosin II?

Answer 31

Myosin I has one head and it’s tail binds to the cell membrane

Myosin II has 2 heads and its tail binds to myosin II