Structure of myosin and actin

Question 1

How is myosin able to move back and forwards?

Answer 1

• myosin filaments have globular head that are hinged which allow them to move back and forwards

Question 2

What is on the globular heads?

Answer 2

on the head is a binding site for each of actin and ATP

Question 3

How is the myosin filament formed

Answer 3

• the tails of several hundered myosin molecules are aligned to form the mysoin filament
• the heads of the myosin molecule protude, while the tails wrap around one another to form the filament

Question 4

What is a myosin molecule?

Answer 4

a globular head with a long tail

Question 5

What do actin filaments have?

Answer 5

• binding sites for myosin heads
• these are called actin-myosin binding sites

Question 6

How are the actin-myosin binding sites blocked?

Answer 6

• often blocked by the presence of another protein called tropomyosin
• which is held in place by the protein troponin

Question 7

What happens when the muscle is in a resting state?

Answer 7

• the actin-myosin sites are blocked by tropomyosin
• the myosin heads can therefore not bind to the actin
• and the filaments cannot slide past each other

Question 8

What happens when a muscle is stimulated to contract?

Answer 8

• the myosin heads form bonds with the actin filaments known as actin-myosin cross-bridges
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Question 9

How does contraction occur?

Answer 9

• the myosin heads flex (change angle) in unison, pulling the actin filament along the myosin filament
• the myosin then detaches from the actin and its head reutnrs to its original angle, using ATP
• the myosin then reattaches further along the actin filament and the process occurs again
• this is repeated up to 100 times per second