Sarcomere structure

Question 1

Describe the arrangements of muscle fibres

Answer 1

Endomysium separates individual muscle fibres
Perimysium lies between fasiculi (bundles of fibres)
Epimysium is the dense sheeth covering the surface

Question 2

Myosatellite cells give rise to what cells?

Answer 2

Myoblasts which will mature into myoctyes. This differentiation process is blocked by myostatin

Question 3

What are myofibrils composed off?

Answer 3

Mainly actin and myosin

Question 4

What is a sarcomere

Answer 4

The portion of a myofibril that lies between two successive Z disks

Question 5

What is a Z disk?

Answer 5

The disk in the middle of an I band. It is involved in differentiating sarcomeres

Question 6

What does the H zone consist of?

Answer 6

Myosin only

Question 7

What does the I band consist of?

Answer 7

Actin only

Question 8

What does the A band consist of?

Answer 8

Myosin and Actin

Question 9

What is the function of the M line?

Answer 9

To hold thick myosin strands together

Question 10

Describe the structure of myosin

Answer 10

Its tail consists of two heavy chains intertwined which lead up to two gloubar heads which extend out forming cross-bridges. The heads contain light bridges along with ATP (myosin-ATPase) and Actin binding sites

Question 11

Describe the structure of Actin

Answer 11

An intertwined contractile protein which is closely associated with Tropomyosin and Troponin. Each G actin has a binding site for myosin

Question 12

Describe the function of Tropomyosin

Answer 12

It is a regulatory protein which overlaps the myosin binding sites on actin and therefore inhibits interaction when in a relaxed state.

Question 13

Describe the function of troponin

Answer 13

It is a regulatory, calcium binding protein which forms a complex with actin and tropomyosin.
Troponin reversibly binds to calcium which changes its conformations to pull tropomyosin away from myosin binding sites allowing for the interaction between actin and myosin.

Question 14

What is the role of Nebulin?

Answer 14

It helps align actin

Question 15

What is the role of Titin?

Answer 15

It provides elasticity and stabilizes myosin

Question 16

Name the structural proteins

Answer 16

Titin, Z-line proteins (alpha actinin), M-line proteins (myomesin, M-protein) and Nebulin

Question 17

Name the contractile proteins

Answer 17

Acin, Myosin, Troponin complex and Tropomyosin

Question 18

What gives cardiac and skeletal muscle their striated appearance

Answer 18

Myofibrils

Question 19

Draw the cross sections through a sarcomere

Answer 19

See week one lecture

Question 20

What are T-tubules?

Answer 20

They are extensions of the cell membrane, its walls are continuous with the sarcolemma so the fluid within the tubules is continuous with the external environment

Question 21

What are the sarcoplasmic reticulum and terminal cisternae

Answer 21

Sarcoplasmic reticulum (SR) is the smooth ER of a muscle cell. The terminal cisternae is the part of the SR that is next to the T-tubules

Question 22

The T-tubule and sarcoplasmic reticulum are connected by what junctions. What proteins are involved in this?

Answer 22

The protein in the T-tubule is a voltage sensitive calcium channels called dihydropyridine. The protein in the SR membrane is known as the ryanodine receptor which forms a Ca channel