Muscle I

Question 1

Skeletal Muscle cell description

Answer 1

Long cylindrical
Also called muscle fibers/myofibers (muscle cell).
Contain HUNDREDS of nuclei on PERIPHERY
Can be slow or fast twitch

Question 2

Myofiber, Myofibril, and myofilament

Answer 2

Myofiber = muscle cell
Myofibril= collection of myofilaments
Myofilaments= actin and myosin

Question 3

Cardiac muscle cell description

Answer 3

A single nucleus, much smaller in diameter and shorter than skeletal muscle.
Distinguishing feature: intercalated disc. Which physically ties together cells so they don’t separate during contraction, and it has gap junction for electrical transmission from one cell to another (AP and heart beat)

Question 4

Smooth muscle cell description

Answer 4

A single nucleus. But are thinner than cardiac cells.
Spindle-shaped, nucleus near center.
NOT striated. But use same proteins and sekeltal and smooth.

Question 5

Sarcomere

Answer 5

Each striated muscle cell has a series of repeating units called the sarcomere.
Basic unit of contraction.
From one Z line to the next.

Question 6

How is force generated?

Answer 6

As thick and thin filaments slide past one another.

Question 7

Myofibrils are covered by

Answer 7

Their own sarcoplasmic reticulum

Question 8

2 main filaments

Answer 8

Thin: actin (f-actin)
Thick: mysoin

Question 9

2 main regulatory proteins

Answer 9

Tropomyosin
Troponin
They bind actin.

Question 10

Thin filament

Answer 10

F-actin. Each thin filament is 1 um long.
Troponin and tropomyosin bind actin.
F-actin is like 2 strings of pearls twisted together (double stranded and helical).

Question 11

Troponin

Answer 11

Binds to tropomyosin at end.
To uncover the binding site..
Intracellular free Ca rises, troponin binds Ca and undergoes a conformational change.
Because troponin binds tropomyosin it can induce a conformational change that exposes the binding sites.

Question 12

Tropomyosin

Answer 12

rod shaped, binds 6-7 actin mlcs of one strand.

Covers binding site for myosin on the actin.

Question 13

Thick filament

Answer 13

Made of mysoin.
Myosin is made of 6 proteins that are really 3 pairs (1 pair of large heavy chains, 2 pairs small light chains).
Each heavy chain forms a long alpha-helical region with a globular head
These wrap around each other to form a long rod with globular heads near each other.
Short, light chains are associated with the globular heads (wrapped around like lever arm).
Myosin heads are staggered along the length of thick filament and around circumference.

Question 14

Myosin head

Answer 14

is where you get interaction with actin.

Actin-myosin combine to contain ATPase activity.

Question 15

Cross-bridge

Answer 15

This is myosin associating with actin.
In relaxed state binding is prevented because binding site on actin is covered by tropomyosin.
After conformational change of tropomyosin, myosin can bind actin.

Question 16

Now let’s talk about the contraction cycle

Answer 16

1.) Myosin binds actin
2.) Force is generated (NO ATP needed, spring is already compressed), energy released upon binding (myosin head rotates relative to neck region where the light chains bind. Pi leaves to generate movement.
3.) Get a shortening of sarcomere
ADP released
4.) Now myosin is stuck to actin until ATP binds. Binding of ATP allows myosin to dissociate from actin.
5.) ATP hydrolysis, not myosin is in a high-energy state (compressing the spring… head cocked in active state)

Question 17

How do you get shortening greater than 8nm?

Answer 17

Get centimeters because

1. ) Lots of sarcomeres in series summate linearly
2. ) Many myosin-actin cycles occur during a single contraction

Question 18

Rate of myosin turnover

Answer 18

Faster in fast twitch (20x/second) than slow twitch muscle (5x/second)