The Structure of Skeletal Muscle - INTERNAL ORGANIZATION OF MUSCLE FIBERS

Question 1

What is part of the internal organization of muscle fibers? (there are 5)

Answer 1

The Myofibrils

The Sarcomere

The Actin Filament

The Myosin Filament

Specializations of Muscle Fibers

Question 2

How many protein strings (cylinders) called Myofibrils are in each muscle cell?

Answer 2

1000

Question 3

Each myofibril contains 3 types of protein called filaments:

Answer 3

a. Actin filament (Thin filament)
b. Myosin filament (Thick filament)
c. Titin filament (Elastic filament)

Question 4

The three filaments form a repeating pattern of fibers called?

Answer 4

the sarcomere:

Question 5

What is Z Lines?

Answer 5

The boundaries of the sarcomere where actin filaments are joined together, forming a zigzag line.

Question 6

What is A Band?

Answer 6

The anisotropic band that extends from the start of the myosin filament to its end. Can also be described as the region of overlapping myosin and actin filaments.

Question 7

What is H Zone?

Answer 7

Region in center of A band where only myosin is present.

Question 8

What is I Band?

Answer 8

The isotropic band, an area of actin filaments next to the Z line.

Question 9

“Light” band due to presence of only actin.

Answer 9

I band

Question 10

What two sarcomeres create a striped or STRIATED appearance in skeletal & cardiac muscle.

Answer 10

The A and I bands

Question 11

“Dark” band due to presence of both myosin & actin. In this area, each thick filament is surrounded by 6 thin filaments.

Answer 11

A band

Question 12

What is the biggest Sarcomere?

Answer 12

A band

Question 13

The actin filament is made up of three proteins:

Answer 13

Actin

Tropomyosin

Troponin

Question 14

Bead-like proteins which form a chain that is twisted

back on itself.

Answer 14

Actin

Question 15

Thread-like protein that winds around the actin

chain so that it covers the active sites (when muscle is relaxed).

Answer 15

Tropomyosin

Question 16

A protein that is attached to tropomyosin

Answer 16

Troponin

Question 17

What does calcium activate in the Actin Filament?

Answer 17

Troponin

Question 18

Active site

Answer 18

Sticky Spot

Question 19

Actin, Tropomyosin and Troponin contains a calcium-binding site therefore what is the outcome?

Answer 19

Calcium must bind

to troponin before muscle contraction can take place. When calcium is

present, troponin acts like a hand and pulls tropomyosin off of the

active sites of the actin. This allows the muscle contraction to start.

Question 20

What is a myosin filament made up of?

Answer 20

100’s of golf-club shaped

myosin proteins.

Question 21

Each myosin has two important parts:

Answer 21

Myosin Rod/Tail

Myosin Head

Question 22

Elongated portion of “golf club” found in the H

zone.

Answer 22

Myosin Rod/Tail

Question 23

What makes up the Myosin Head?

Answer 23

1) Hinge region—A bendable neck region that attaches the head

to the rod. Bending of the hinge region causes swinging of the

myosin head.

2) ATP-binding region—ATP is energy; It is needed for the

movement of the myosin head.

Question 24

What are T Tubules?

Answer 24

Transverse Tubules

Question 25

1. What is the purpose of T- tubules?
2. How does this work?

Answer 25

1. Carry electrical currents (made by nerves) from the surface of the
   muscle cell to its center.
2. This means that the electrical current reaches
   all myofibrils of the cell, not just the outer myofibrils, so that they all
   contract within the muscle cell.

Question 26

A special organelle located
between T-tubules that stores calcium

Answer 26

Sarcoplasmic Reticulum

Question 27

What is the cycling of calcium by Sarcoplasmic Reticulum (SR)?

Answer 27

1. When the muscle is relaxed Calcium is stored in SR.
2. To start a contraction- Calcium is released on to muscle sarcomeres.
3. To stop the contraction, Calcium is returned to the SR.