Section 1

Question 1

Describe the distinctive features of the sarcomere as seen under a light microscope

Question 2

Describe the functions of the skeletal muscle contractile proteins

Question 3

What are the three types of muscle?

Answer 3

Skeletal, smooth and cardiac

Question 4

Skeletal muscle is _______ and under _______ control.

Answer 4

Skeletal muscle is STRIATED and under VOLUNTARY control.

Question 5

Is skeletal muscle under involuntary or voluntary control?

Answer 5

Voluntary

Question 6

Which neurotransmitter innervates the muscle at the neuromuscular junction?

Answer 6

Acetylcholine (Ach)

Question 7

A whole skeletal muscle is made up of individual _________________, each of which runs the entire length of the muscle.

Answer 7

A whole skeletal muscle is made up of individual muscle fibres, each of which runs the entire length of the muscle.

Question 8

Describe muscle fibers

Answer 8

• run parallel to each other
• surrounded by connective tissues
• a muscle fiber is a single muscle cell
• multinucleated and have very large number of mitochondria

Question 9

What are myofibrils?

Answer 9

Discrete, contractile elements that are divided up along the length of a muscle fiber

Question 10

Describe how a myofibril would look when viewed from the side using a light microscope?

Answer 10

It would display a pattern of light and dark bands that give the muscle fiber a striated pattern

Question 11

Describe what a cross section of myofibril would look like.

Answer 11

A highly organized cytoskeletal pattern of thick and thin filaments (thick myosin and thin actin)

Question 12

What are A bands?

Answer 12

• aka dArk bands
• made up of stacked thick and thin filaments that are aligned parallel to each other
• the middle of the A bind is slightly lighter since the thin filaments do not reach this far from the ends
• the lighter portion is also called the H zone

Question 13

What are the I bands?

Answer 13

• aka lIght bands
• made up of the part of the thin filaments that do not extend into the A band
• in the middle of the I band is a vertical line called the Z line

Question 14

What is the H zone?

Answer 14

• the slightly lighter portion of the A band
• contains proteins that hold the thick filaments, myosion, together in a stack
• Myosin is composed of 2 heavy chains and 2 light chains and the H zone contains the HEAVY CHAINS
• these proteins are seen as the M line running down the middle of the H zone

Question 15

What is the M line?

Answer 15

• the proteins that hold the thick filaments together in a stack are seen as the M line
• runs down the middle of the H zone

Question 16

What is the Z-line

Answer 16

• the middle of the I band
• distance from one z-line to the next is a sarcomere

Question 17

What is the distance from one Z-line to the next called?

Answer 17

A sarcomere

this is what we consider to be the functional unit of skeletal muscle

Question 18

How do muscles extend the length of the muscle fiber when they’re growing?

Answer 18

My adding new sarcomeres onto the ends

Question 19

What does the area in the A band where the thick and thin filaments overlap contain?

Answer 19

Cross-bridges that extend from the thick filaments and form when thin filaments bind

(mobile myosin heads bind to actin molecules in muscles)

Question 20

Describe the thick filament

Answer 20

• composed of myosin
• each myosin molecule is a dimer of two subunits
• each subunit looks like a golf club (has a long shaft with a globular head)

When the dimers come together, the “shaft” or tail portions wrap around each other. Within a thick
filament, two dimers come together in a tail-to-tail formation and then these stack up with other myosin molecules. The heads stick out and contain two important sites, an actin binding site, and a
myosin ATPase site.

Question 21

What is myosin?

Answer 21

(a motor protein that uses ATP to move along actin filaments)

Question 22

Describe the thin filament.

Answer 22

The thin filament is made up of the proteins actin, tropomyosin and troponin. The main structural component is two actin filaments

Question 23

What are actin filaments?

Answer 23

Actin filaments are made up of individual spherical actin molecules that come together to form a
double helix structure

Question 24

What is tropomyosin?

Answer 24

a thin, double helix protein that lies end to end along the actin helix structure.

It is a regulatory protein that covers the active binding sites, preventing the interaction of actin and myosin

Question 25

What is troponin?

Answer 25

is a regulatory protein complex made of three polypeptides. One binds to tropomyosin, one bind to actin, one binds to Ca2+