Nerve Muscle Synapse Lecture 7

Question 1

What are the 6 key molecular participants in the sliding filament theory of muscle contraction?

Answer 1

1. Myosin (thick filament)
2. Actin (thin filament)
3. Tropomyosin - regulatory protein that binds to actin
4. Troponin - binds actin and tropomyosin - site of calcium binding
5. ATP
6. Ca2+ - released from sarcoplasmic reticulum

Question 2

Which protein is a regulatory protein that binds to actin

Answer 2

Tropomyosin - regulatory protein that binds to actin

Question 3

Which protein binds actin and tropomyosin and is the site of calcium binding

Answer 3

Troponin

Question 4

Myosin has two binding sites: one that binds to ____ and the other that binds to _____

Answer 4

Myosin has two binding sites: one that binds to ATP and the other that binds to actin

Question 5

How does myosin move from low energy state to the high energy state?

Answer 5

By hydrolyzing a molecule of ATP

Question 6

In an unstimulated muscle. the position of the ______ covers the binding sites on the actin subunits preventing the myosin cross-bridges from forming

Answer 6

In an unstimulated muscle. the position of the tropomyosin covers the binding sites on the actin subunits preventing the myosin cross-bridges from forming

Question 7

_____ is a component of the thin filament that has a binding site for calcium

Answer 7

troponin

Question 8

How does troponin facilitate the movement of tropomyosin allowing the actin molecule binding to be accessed by the myosin?

Answer 8

Ca2+ released from the terminal cisternae bind to troponin

Causes a conformation change in the tropomyosin-troponin complex “dragging” the tropomyosin off the binding site

Question 9

What are the 6 steps of cross-bridge cycling (muscle contraction)?

Answer 9

1. The influx of calcium triggering the exposure of binding sites on actin
2. The binding of myosin to actin
3. The “power stroke” of the cross-bridge that causes the sliding of the thin filaments
4. the binding of ATP to the cross-bridge = cross-bridge disconnects from actin
5. hydrolysis of ATP = reenergizes and repositions the myosin cross-bridge = allows another cycle
6. the transport of calcium back into the sarcoplasmic reticulum

Question 10

What happens PRIOR to cross-bridge cycling?

Answer 10

Muscle AP propagated through the T-tubule system, causing the release of calcium from the sarcoplasmic reticulum into the cytosol.

Coupling is through DHP and ryanodine receptor

Question 11

Cross bridge cycling:

Calcium binds to _____ causing a change in the ________ complex = exposes myosin binding sites on actin

Answer 11

Cross bridge cycling:

Calcium binds to troponin causing a change in the troponin-tropomyosin complex = exposes myosin binding sites on actin

Question 12

The energy from the _____ of ATP puts the myosin head in its ______ state

Answer 12

The energy from the hydrolysis of ATP puts the myosin head in its High-energy state

Question 13

The pivoting of the ______ causes the H-zone to shorten.

Answer 13

The pivoting of the myosin cross-bridge causes the H-zone to shorten.

Question 14

What is important about when myosin binds to actin in terms of ATP?

Answer 14

Remember: when things bind there is a conformation change = actin binding to myosin = conformation change of myosin = ADP and Pi are booted off the myosin molecule

Question 15

In cross-bridge cycling, the _____ energy of ATP is transformed into the _____ energy of contraction

Answer 15

In cross-bridge cycling, the chemical energy of ATP is transformed into the mechanical energy of contraction

Question 16

What causes the disconnecting of Actin and myosin?

What are two examples when we don’t have enough ATP to allow the myosin to dissociate from the actin?

Answer 16

The binding of Actin on myosin = conformation change

1. Muscle cramp = not enough ATP
2. Rigor mortis = no ATP following death

Question 17

The release of myosin cross-bridge from actin triggers:

Answer 17

Hydrolysis of ATP into ADP and Pi = myosin returns to high-energy conformation = binds to Actin

Question 18

The powerstroke moves the _______ inward, shortening the ______

Answer 18

The powerstroke moves the thin filament inward, shortening the sarcomere

Question 19

What are two situations of muscle contraction where ATP is required:

Answer 19

1. Binding of ATP is essential for the release of myosin cross-bridge from actin
2. the hydrolysis of ATP is essential for re-energizing and repositioning the Myosin molecule to begin another cross-bridge cycle (allowing myosin to bind to actin)

Question 20

During contraction, all cross-bridges are neither ____ nor _____ at the same time

Answer 20

During contraction, all cross-bridges are neither bound nor disconnected at the same time

Question 21

What are the two metabolic variations of muscle fibres?

Answer 21

White and Red

Differ in size and colouration

Question 22

What causes the colour variation in the different types of muscle fibres?

Answer 22

Their different methods of synthesizing ATP

Question 23

Which Muscle Fibre:

• Large diameter
• Reduced myoglobin
• surrounded by few capillaries (low amounts of O2)
• relatively few mitochondria
• high glycogen content

Answer 23

White Muscle Fibres

Question 24

White muscle fibres are used for _____ _____ activity

Answer 24

Short, intense

(powerlifting)

Question 25

Which muscle fibre: * smaller diameter * Large quantity of myoglobin * surrounded by many capillaries (high O2) * Numerous mitochondria * Low glycogen content

Answer 25

Red Muscle fibres

Question 26

Red muscle fibres synthesize ATP ______ than white muscle fibres

Answer 26

Slower

Question 27

What kind of activity are red muscle fibres more important for

Answer 27

Long lasting, continuous, light muscle contraction

Question 28

How does white muscle fibre generate ATP

Answer 28

Glycolysis - anaerobic

Question 29

How do Red muscle fibres generate ATP?

Answer 29

Oxidative phosphorylation and the Krebs Cycle (aerobic)

Question 30

"fast twitch glycolytic fibres" refers to what

Answer 30

White muscle fibres

Question 31

"Slow twitch oxidative fibres" refers to?

Answer 31

Red Muscle Fibres