Sarcomere Structure

Question 1

Describe the T tubules

Answer 1

• Walls are continuous with the sarcolemma

* Fluid within is continuous with the external environment

Question 2

Describe how the T tubules and the sarcoplasmic reticulum are connected

Answer 2

With junctions: involve 2 integral membrane proteins, one in the T tubule membrane and the other in the membrane of the sarcoplasmic reticulum

Question 3

What is the Sarcolemma?

Answer 3

True cell membrane and encloses the muscle fibre

Question 4

What is the role of Titin?

Answer 4

• To provide elasticity and stablilize the myosin

Question 5

What is the Myofibril?

Answer 5

Predominately composed of actin and myosin filaments

Question 6

Describe the ultrastructural basis of the I band

Answer 6

• Actin filaments bisected by the Z line

Question 7

Where is the Endomysium?

Answer 7

Separates the muscle fibres

Question 8

Describe the ultrastructural basis of the H zone

Answer 8

Region of A band which contains only myosin filaments

Question 9

Define a sarcomere

Answer 9

The portion of a myofibril that lies beween 2 successive z disks

Question 10

Describe Tropomyosin

Answer 10

• Regulatory protein

* Overlaps the binding sites of actin for myosin and inhibits interaction when in the relaxed state

Question 11

Describe Troponin

Answer 11

• Regulatory, calcium binding protein
• Forms a complex with the other proteins of the thin filament (actin and tropomyosin)
• Binds to Ca2+ reversibly and once bound, changes conformation to pull the tropomyosin away from the myosin interaction sites
• Ca2+ binding to troponin regulates skeletal muscle contraction because it moves the tropomyosin away and allows myosin to interact with the actin

Question 12

Describe the T tubule protein

Answer 12

• Modified voltage-sensitive Ca2+ channel

* Dihydropyridine receptor

Question 13

What are muscle fibres arranged in?

Answer 13

Bundles of fasiculi

Question 14

What are the contractile proteins of the sarcomere?

Answer 14

• Actin
• Myosin
• Tropomyosin
• Troponin complex

Question 15

Describe the protein found in the SR membrane

Answer 15

• Ryanodine receptor

* Forms a Ca2+ channel

Question 16

What is a muscle fasicle wrapped in?

Answer 16

Perimysium

Question 17

Describe the ultrastructural basis of the A band

Answer 17

• Primarily myosin filaments in the region overlap

Question 18

What are the structural proteins of the sarcomere?

Answer 18

• Titin (connection)
• Z line protein (alpha-actinic)
• M-line proteins (myosin, M protein)
• Nebulin

Question 19

What is a thin filament?

Answer 19

Actin filament

Question 20

What is the Sarcoplasm?

Answer 20

Intracellular fluid that fills spaces between myofibrils

Question 21

How many thick filaments surround a thin filament?

Answer 21

3

Question 22

What is the role of nebulin?

Answer 22

Helps to align the actin

Question 23

What gives skeletal muscle its striated appearance?

Answer 23

Myofibrils- the orderly arrangements of thick and thin filaments

Question 24

What is a thick filament?

Answer 24

Myosin filament

Question 25

Where is the Epimysium?

Answer 25

Dense sheath on the surface

Question 26

Describe myosin

Answer 26

• Tail consists of two intertwined heavy chains
• Two globular heads extend out, forming cross bridges
• Globular heads contain heavy and light chains and binding sites for acid and ATP (mysosin ATPase)

Question 27

How many thin filaments surround a thick filament?

Answer 27

6

Question 28

What are the defining characteristics of skeletal muscle?

Answer 28

1. Multinucleated
2. Many mitochondria
3. Transverse tubules
4. Myofibrils and sarcomeres
5. Sarcolemma, Sarcoplasm and Sarcoplasmic reticulum

Question 29

Where is the Perimysium?

Answer 29

Lies between fasiculi

Question 30

Describe actin

Answer 30

• Contractile protein

* Each G actin has a binding site for myosin