Overview of muscle contraction

Question 1

What is a muscle fibre ?

Answer 1

Large, single, elongated, multinuclear cell

Question 2

What does each fibre contain?

Answer 2

About 1,000 myofibrils, each consisting of thick and thin filaments and surrounded by sarcoplasmic reticulum

Question 3

What is a sarcomere ?

Answer 3

Muscle cells contain numerous myofibrils, consisting of interlocking thick and thin filaments arranged into repeating units

Question 4

What are the thick and thin filaments are made of ?

Answer 4

Different proteins and form a striated pattern when viewed under the microscope

Question 5

What are filaments anchored by ?

Answer 5

Titin to the Z-disk

Question 6

What are t-tubules ?

Answer 6

Invaginations off the plasma membrane

Question 7

What is the sarcoplasmic reticulum (SR) ?

Answer 7

The specialised muscle ER

Question 8

What is an A band ?

Answer 8

Stretches the length of the thick filament

Question 9

What is an I band ?

Answer 9

Contains only thin filaments

Question 10

What is the Z disk ?

Answer 10

Attachment site for thin filaments

Question 11

What is the M line ?

Answer 11

Bisects the A band

Question 12

During contraction there is a decrease in sarcomere length by ?

Answer 12

Reduction of the I band, with no change in the width of the A band

Question 13

Thick and thin filaments slide along one another but do not change in?

Answer 13

Length

Question 14

The thick filaments consist of?

Answer 14

Myosin molecules

Question 15

Thin filaments consist of?

Answer 15

Actin, with tropomyosin, and the troponin complex

Question 16

The troponin complex is involved in ?

Answer 16

The regulation of muscle contraction

Question 17

What are the two heavy chains that myosin has ?

Answer 17

The carboxyl termini forming an extended coiled coil (tail) and the amino termini having globular domains (heads) with ATPase activity.

Question 18

What is F-actin composed of?

Answer 18

G-actin monomers that polymerize two by two, giving the appearance of two filaments spiraling about one another in a right-handed fashion

Question 19

Each actin monomer in the thin filament binds to ?

Answer 19

One myosin head group

Question 20

Availability of myosin-binding sites on actin is regulated by? and avoids ?

Answer 20

Troponin and tropomyosin.

- avoids continuous muscle contraction

Question 21

Troponin Complex:
Troponin I = ?
Troponin C = ?
Troponin T = ?

Answer 21

Troponin I = inhibitory subunit
Troponin C = calcium binding subunit
Troponin T = tropomyosin binding subunit

Question 22

Nerve impulse triggers release of Ca2+ causing ?

Answer 22

Conformational changes to tropomyosin-troponin complex, exposing myosin-binding sites

Question 23

Skeletal muscle contraction is regulated by ?

Answer 23

A Ca2+-dependent thin filament-based regulatory mechanism

Question 24

Sarcomere Ca2+ concentration is regulated by?

Answer 24

Release and uptake into the sarcoplasmic reticulum (SR)

Question 25

ATP binding causes?

Answer 25

Release of myosin from thin filament

Question 26

Hydrolysis of ATP rotates myosin into ?

Answer 26

“Cocked” state

Question 27

What is a power stroke caused by ?

Answer 27

Release of phosphate