CMB1004/L11 Muscle Contraction

Question 1

What are muscle fibres made up of?

Answer 1

Myofibrils

Question 2

What are the stripe-like repeating units in muscles?

Answer 2

Sarcomeres

Question 3

What are the lines between sarcomeres called?

Answer 3

Z-line (disc)

Question 4

What is the part of the sarcomere only containing thick filaments called?

Answer 4

H zone

Question 5

What is the part of the sarcomere containing only thin filaments called?

Answer 5

I band

Question 6

What is the part of the sarcomere containing thick filaments and overlap with thin filaments called?

Answer 6

A band

Question 7

During muscle contraction, what happens to the A band?

Answer 7

Remains the same

Question 8

During muscle contraction, what happens to the I band?

Answer 8

Length decreases

Question 9

During muscle contraction, what happens to the H zone?

Answer 9

Length decreases

Question 10

During muscle contraction, what happens to the Z line?

Answer 10

Distance between Z lines decreases

Question 11

What are thick filaments made of?

Answer 11

Myosin

Question 12

What holds thick filaments together?

Answer 12

M line

Question 13

What are thin filaments made of? (3)

Answer 13

Actin, tropomyosin & troponin

Question 14

How many myosin binding sites does each G-actin molecule have?

Answer 14

1

Question 15

How many F-actin strands wind together in a double helix in thin filaments?

Answer 15

2

Question 16

What winds around the F-actin double helix in thin filaments?

Answer 16

Long filaments of tropomyosin

Question 17

How many subunits does troponin have and what are they called?

Answer 17

3
T, I & C

Question 18

What type of protein is troponin?

Answer 18

Trimeric

Question 19

Which of tropomyosin’s subunits bind to actin and tropomyosin in thin filaments?

Answer 19

T & I

Question 20

What occurs when Ca2+ binds to troponin’s C subunit in thin filaments?

Answer 20

Myosin binding site is uncovered

Question 21

What does binding of troponin’s T & I subunits binding to tropomyosin and actin cause in thin filaments?

Answer 21

Blocking of myosin binding site

Question 22

What are T-tubules?

Answer 22

Invaginations of muscle membrane that penetrate deep into muscle fibre

Question 23

What is each myofibril surrounded by?

Answer 23

Sarcoplasmic reticulum

Question 24

What does the sarcoplasmic reticulum enlarge into near T-tubules?

Answer 24

Terminal cisternae

Question 25

What is a triad in muscle fibres?

Answer 25

T-tubules and neighbouring sarcoplasmic reticulum on either side of muscle fibres

Question 26

What is stored in large quantities in muscle fibres?

Answer 26

Ca2+

Question 27

What is the function of T-tubules? (2)

Answer 27

Allows action potential into parts of the muscle that other membranes can’t reach
Triggers Ca2+ release from TC of SR via specialised Ca2+ release channels

Question 28

Describe excitation-contraction coupling. (7)

Answer 28

Ca2+ binds to troponin-C
Myosin binding site uncovered
Myosin hydrolyses ATP
Myosin heads rotate
Pulls thin filaments towards centre of sarcomere
ATP binds to myosin head
Myosin released from troponin-C

Question 29

What is a powerstroke?

Answer 29

Rotation of myosin heads, pulling thin filaments towards centre of sarcomere

Question 30

What is a cross-bridge formation?

Answer 30

Formation of bond between actin and myosin

Question 31

How many myosin heads does a typical muscle fibre have?

Answer 31

500

Question 32

How many cycles per second occur during rapid muscle contraction?

Answer 32

5

Question 33

What is required for muscle relaxation? (2)

Answer 33

Removal of Ca2+ by sarcoplasmic reticulum via Ca2+-ATPase pump
ATP binding to myosin