Muscle Contraction

Question 1

State heirarchial structure of muscle.

Answer 1

Muscle –> bundles (fasciculi) –> fibres (cells) –> myofibrils (subcellular unit)

Question 2

How many actin filaments around each myosin?

Answer 2

6, hexagonally arranged.

Question 3

What does the A band consists of?

Answer 3

Area of myosin + actin overlap IN ADDITION TO THE H ZONE.

Question 4

What is the structure of a myosin molecule?

Answer 4

2 heavy chains (these are responsible for contraction), 4 light chains.

Question 5

What are the components of troponin?

Answer 5

Tn-C (calcium binding), Tn-I (inhibitory) and Tn-T (tropomyosin binding)

Question 6

Outline the main stages of muscle contraction.

Answer 6

1) When no Ca2+ present, myosin is bound to ADP + Pi.
2) Ca2+ enters, and Myosin head binds to actin
3) Pi dissociates, and myosin pulls actin.
4) ATP binds and is hydrolysed to ADP + Pi. Myosin head releases, resets and binds to actin again if Ca2+ still present.

Question 7

Outline muscle contraction differently.

Answer 7

1) After myosin has pulled Actin, ATP binds and hydrolyses to ADP + Pi.
2) Myosin releases, resets and binds to actin.
3) Pi is released and myosin pulls.

Question 8

What happens in the presence of Ca2+

Answer 8

Ca2+ binds to Tn-C, which induces changes through Tn-I –> Tn-T which moves tropomyosin.

Question 9

Name 2 types of muscular dystrophy

Answer 9

Becker & Duchenne

Question 10

What are the main features of duchenne muscular dystrophy?

Answer 10

X linked recessive. No cure. Progressive muscle weakness/atrophy.

Question 11

What are ryanodine receptors?

Answer 11

Calcium channels on Sarcoplasmic reticulum. Sensitive to T-Tubule depolarisation.

Question 12

How do ryanodine receptors work?

Answer 12

1) T-tubule depolarises
2) DIHYDROPYRIDINE (voltage gated Ca2+ channel) opens Ryanodine Receptor
3) Open ryanodine receptor permits movement of Ca2+ from SR into Sarcoplasm.

Question 13

What is malignant hyperthermia?

Answer 13

Genetically inherited. Defective ryanodine receptors. Triggered by general anaesthetics. Excessive release of Ca2+ by Ryanodine receptors. –> hypermetabolism, muscle rigidty etc.

Question 14

Name 3 sources of high energy phosphate that can maintain ATP levels.

Answer 14

1) Glycogen
2) Cellular Respiration
3) creatine phosphate

Question 15

What is creatine phosphate?

Answer 15

Bridges gap between depletion of ATP and glycogenolysis. (short bursts of energy).

Question 16

How does creatine phosphate release ATP?

Answer 16

Creatine Phosphate + ADP –> Creatin + ATP.

This is catalysed by CREATINE KINASE