Lecture 15

Question 1

Main Myosin

Answer 1

Myosin II

Question 2

Structure of myosin

Answer 2

-Dimer
Each dimer has a heavy and light chain and a long alpha-helices tail and hinge region

Question 3

Role of the heavy chain?

Answer 3

-Binds and interacts with ATP (force generating)

Question 4

Where does myosin walk?

Answer 4

Toward the plus end of actin

Question 5

When myosin is not bound to ATP/ADP ?

Answer 5

Myosin head domain(heavy chain) associates with the actin filament

Question 6

When myosin is bound to ATP?

Answer 6

Reduces the affinity of the myosin head to actin and induces a conformational change

Question 7

Myosin head when bound to ADP + Pi?

Answer 7

Hydrolysis of ATP causes head group to cock toward plus end of actin

Question 8

Myosin head releases ADP?

Answer 8

Myosin head rebinds actin and head shifts back to regular position

Question 9

Are both myosin domains coordinated?

Answer 9

No

Question 10

Myofibrils?

Answer 10

Many actin and myosin together in muscles

Question 11

Sarcomere?

Answer 11

Actin surrounding myosin molecules in cylindrical fashion

Question 12

CapZ in sarcomeres?

Answer 12

The plus end is bound by CapZ in sarcomeres to prevent the addition of monomers

Question 13

Tropomodulin sarcomeres?

Answer 13

The minus end is bound by tropomodulin which prevents the addition of monomers to the minus end

Question 14

What happens to tropmyosin when calcium is released?

Answer 14

Troponin which is bound to tropomyosin binds the calcium and then pushes tropomyosin out of the way from the myosin binding site

Question 15

What regulates non-muscle myosin?

Answer 15

Phosphorylation

Question 16

Myosin light chain kinase?

Answer 16

Phosphorylates non muscle myosin and causes it to unfold into its active state, now it can interact with actin

Question 17

Why would a cell want non-muscle myosin?

Answer 17

Cytokinesis

Question 18

Cytokinesis

Answer 18

Near where the cells will divide there is a bunch of myosin light chain kinases that phosphorylate the myosin light chains so that it is in its active form and can assemble with actin. Contraction of actin helps divide the cell

Question 19

What are microtubules made up of?

Answer 19

Tubulin subunits (dimers) either beta or alpha

Question 20

Alpha and Beta subunits and GTP

Answer 20

-Both subunits can combine with GTP
-Alpha GTP cannot hydrolyze
-Beta GTP can hydrolyze

Question 21

How do microtubules assemble ?

Answer 21

Alpha-beta tubulin subunits can assemble in a head to tail fashion into protofilaments. 13 protofilaments then form a hollow tube.

Question 22

What is the plus end of the microtubule?

Answer 22

Beta subunits

Question 23

Why are microtubules stiffer than actin?

Answer 23

Form bonds with multiple subunits on many sides

Question 24

T/F: nucleation in microtubules is not spontaneous

Answer 24

True

Question 25

Plus end vs Minus end of microtubules ?

Answer 25

Site of nucleation is the minus end -Growth of the filament occurs at the plus end normally

Question 26

Free tubulin subunits are bound by?

Answer 26

GTP and have high affinity for other tubulins

Question 27

GDP bound subunits?

Answer 27

Have less affinity for tubulin

Question 28

GTP-cap

Answer 28

When new GTP-bound subunits are added quickly enough a stable GTP cap is bound and the microtubule is less likely to dissociate

Question 29

Do microtubules treadmill?

Answer 29

No

Question 30

No GTP bound cap?

Answer 30

Catastrophic event

Question 31

What happens when GDP subunits reach the end of the microtubule?

Answer 31

-Subunits start curving and peel away from the microtubule -Microtubule will shrink to nothing

Question 32

Dynamic Instability?

Answer 32

Growing/shrinking of microtubules

Question 33

Microtubule Nucleating proteins?

Answer 33

-Gamma tubulin -Augmin

Question 34

Gamma tubulin and nucleation?

Answer 34

2 gamma tubulin associate into the gamma tubulin small complex. This complex mimics the plus end of a microtubule and binds alpha-subunits

Question 35

Gamma tubulin ring structure?

Answer 35

7 gamma tubulin small complexes assemble into a ring structure and all start growing (14 exposed gammma tubulins but one is a binding site to close the ring, so 13 protofilaments created)

Question 36

Microtubule Organizing Center?

Answer 36

A collection of gamma tubulin ring complexes

Question 37

Example of an MTOC?

Answer 37

Centrosome

Question 38

Centrioles?

Answer 38

These are microtubules which bind to the centrosome and grow/shrink Minus end is in the ring complex and plus end grows outward