Module 4 Lecture 2

Question 1

Are myofibrils cells?

Answer 1

No they’re actually rods that are found in cells (muscle fibre)

Question 2

If myosin is bound to the Z-line via titin, how does actin bind to the Z-line?

Answer 2

Directly connnected to the Z line

Question 3

When the myosin binds to actin to pull it and cause contraction, what specifically is it pulling?

Answer 3

It is pulling the sarcomeres closer to one another

Note: Pulling the sarcomeres together does not mean that the proteins are being squished or shortening

Question 4

What are the sources of energy that let myosin bind to actin

Answer 4

1. Calcium
2. ATP

Question 5

Geometrical structure of actin and myosin? Why is it the way it is?

Answer 5

• Every actin has 3 myosin surrounding it
• Every myosin has 6 actin surrounding it

The reason it’s this way is because when muscle gets damaged they need to be formed in this way so that muscle is regenerated to look how it should

Question 6

Myosin heads are also referred to as?

Answer 6

Cross-bridges

Question 7

When muscle is torn and being fixed by satellite cells, striations start to appear. What is that called?

Answer 7

When striations start to appear after muscle is fixed, it is called differentiation

Question 8

What is actin?

Answer 8

A long polypeptide globular structure covered by rope structure called tropomyosin which is bound by tri peptide protein called troponin

Question 9

Where on the myosin is the “actin binding site”?

Answer 9

The very end of the myosin head binds to actin

Question 10

What is an actin filament and an actin molecule?

Answer 10

• Actin filament is the entire chain including the two rows of actin that are twisted around each other
• Actin molecule refers to each individual globule

A single myosin binds to a single actin molecule binding site

Question 11

What is tropomyosin

Answer 11

A protein which is essentially a rope that wraps around the actin and is attached to it by another protein called troponin

Question 12

How can troponin affect the movement of tropomyosin

Answer 12

Either triggered to make tropomyosin stay on the binding site or triggered to move tropomyosin out of the way

Question 13

What are the subunits of the troponin?

Answer 13

T, tropomyosin = Troponin is gripping onto tropomyosin holding the troponin complex
I, inhibitory = Also bound to tropomyosin but prevents it from moving off the actin
C, calcium = binding site of calcium

Question 14

What happens when calcium binds to the troponin c subunit

Answer 14

When it binds to the C subunit, it causes the tropomyosin to roll over exposing the actin binding sites

Troponin and tropomyosin are considered regulatory proteins

Question 15

How many actin globules does a tropomyosin cover?

Answer 15

1 tropomyosin rope like structure protein covers only 7 actin molecule binding sites

Question 16

What is a myosin filament?

Answer 16

A repeating myosin molecule but a single myosin molecule looks like a hockey stick

Question 17

How many tails and heads does a single myosin molecule have and how many heavy chains do they have?

Answer 17

Single myosin molecule = 2 heads and 2 tails
* One heavy chain is one head and one tail
* One heavy chain is one head and one tail

• Therefore, a single myosin molecule has two heavy chains wrapped around each other.

Heavy chain = 1 head, 1 tail

Question 18

What are light chains?

Answer 18

Regulate whether or not myosin is going to bind actin efficiently

Question 19

Structure of the myosin molecule includes?

Answer 19

2 large polypeptide heavy chains + 4 smaller light chains