8.1 Muscle Contraction & Locomotion

Question 1

What occurs when ATP binds to myosin?

Answer 1

ATP binding releases myosin from actin

Question 2

Describe the process (cycle) whereby myosin ATPase activity moves actin filaments.

Answer 2

1. ATP binds to myosin head. Myosin releases from actin 2. Hydrolysis of ATP to ADP +inorganic phosphate. This changes myosin head to be in the open position. 3. Release of Pi = reattachment of myosin to new actin subunit 4. Release of ADP = myosin head moves to closed position/resting shape

Question 3

What is the role of colifin protein in cell migration?

Answer 3

(Colifin = actin depolymerizing factor) Preferentially binds ADP actin rather than ATP actin.

Question 4

What would be the distributions of cofilin and the Arp2/3 complex in a lamellar protrusion?

Answer 4

Arp2/3 complex at the leading edge= nucleating of actin (nucleated actin attaches to sides of pre-existing filaments) Cofilin is at the trailing edge = DISASSEMBLY/depolarize get old actin

Question 5

Myosin heads can only bind to actin when _______.

Answer 5

Tropomyosin is moved. This happens when calcium is bound to Troponin.

Question 6

Sliding filament theory

Answer 6

Each sacromere shortens as the thin filament slides closer together between the thick filaments so that the Z-disk are pulled closer together

Question 7

Troponin C

Answer 7

Binds calcium

Question 8

Troponin T

Answer 8

Binds to the tropomyosin itself.

Question 9

Troponin I

Answer 9

Links the two other Troponin proteins together.

Question 10

Tropomyosin

Answer 10

Protein. Function= prevent the attachment of myosin heads to the actin filament in muscle cells.

Question 11

All Myosin heads (except VI) move towards the ___ end of the actin filament.

Answer 11

+ end

Question 12

Myosin I contains ____heads.

Answer 12

One head

Question 13

Myosin II contains ____heads?

Answer 13

Two heads.

Question 14

Changes in the length of the myosin arm =

Answer 14

changes in speed and magnitude of force of the myosin head that it can use to apply to the actin filament

Question 15

Contraction is achieved by moving two points in a cell _____

Answer 15

towards each other.

Question 16

The class of myosin always involved in contraction is _______.

Answer 16

Myosin type II. It has a long tail domain used for dimerization and thick filament assembly.

Question 17

Myosin filaments are considered to be

A. bipolar

B. non-polar

C. polar

Answer 17

Bipolar filaments due to the direction the heads are pointing. One direction on one end of the thick filament, the opposite direction at the other end.

Question 18

The center of a myosin filament is _____.

Answer 18

Bare. No myosin heads = the bare zone.

Question 19

How is smooth muscle contraction regulated? (short explanation)

Answer 19

Phosphorylation of myosin light chains by myosin light chain kinase.

Question 20

When myosin light chains are phosphorylated _____.

Answer 20

Active state = The myosin tail is released from it’s conformation. It straightens out so it can form the myosin thick filaments. Contraction can then occur.

Question 21

When the myosin light chains are not phosphorylated ______.

Answer 21

Inactive state = Myosin light chains are sticky and attach to the myosin tail domain. This causes the tail to be bent and unable to form the thick filament.

Question 22

alpha actinin

Answer 22

Holds actin filaments together in loose bundles in smooth muscle.

Question 23

Dense plaques

Answer 23

Strong anchor sites for actin filaments in smooth muscle cells. While in relaxed state, the actin is held in position by dense plaques in a monomeric state.

Question 24

Smooth muscle cell contraction

Answer 24

Occurs when myosin light chains are phosphorylated, thick filaments can form, they pull on the actin filaments and shorten the cell.

Question 25

Why is skeletal muscle striated?

Answer 25

Striations in muscle cell is due to the highly ordered arrangement of actin and myosin filaments causing a “banded” look.

Question 26

Muscle fiber contains many ______.

Answer 26

Myofibrils

Question 27

Sacromere

Answer 27

The distance between Z-lines of the thin filaments (thick filament inbetween)

Question 28

Skeletal muscle contracts only when stimulated by a ______.

Answer 28

somatic motor unit.

Question 29

Motor unit

Answer 29

nerve fiber + muscle fiber

Question 30

Sarcolemma

Answer 30

The membrane surrounding the muscle fiber. This is the location of the ion channel receptors which receive the acetylcholine delivered by the axon terminal of the motor neuron.

Question 31

T-tubule

Answer 31

Sits on the outside, around the outside of the myofibril. The T-tubule contains the calcium ion channels. The T-tubule is surrounded by the sarcoplasmic reticulum, which holds the calcium.

Question 32

Which is bigger? Skeletal or smooth muscle cells?

Answer 32

Skeletal muscle cells are much bigger and contain many nuclei.

Question 33

I-band

Answer 33

Isotropic. Light bands….contain the Z-disk line.

Question 34

A-band

Answer 34

Anisotropic. Dark bands. Contain the M-line and H-zone. They look dark because of the density of protein in this area.

Question 35

Titin

Answer 35

Anchors the myosin thick filament to the Z-line.

Question 36

Nebulin

Answer 36

Actin associated protein which binds to actin filaments and acts as a ruler to determine their length.

Question 37

Cap Z

Answer 37

Protects the + end of the actin filaments (at the Z-line).

Question 38

Tropomodulin

Question 39

Which, if any of the bands we talked about, changes length as contraction occurs?

Answer 39

Titin spring protein shortens. Thick and thin filaments slide past each other but do not change length.

Question 40

Terminal cisternae

Answer 40

The ends of the sarcoplasmic reticulum where they meet the transverse tubule.