Myosin II

Question 1

What is the repeating unit of myofibrils?

Answer 1

Sarcomere

Question 2

Why does actinomyosin have semicrystalline properties?

Answer 2

Repeating sarcomere structure

Question 3

What is the structure of myosin II?

Answer 3

• Dimer of 2 heavy chains
• Long coiled-coil domain

Question 4

Does myosin II have a cargo binding domain?

Answer 4

No

Question 5

How many IQ motifs does the lever arm of myosin have?

Answer 5

2

Question 6

What regulates the powerstroke in myosin II?

Answer 6

The lever arm

Question 7

Which direction does myosin II move?

Answer 7

towards the plus end of actin

Question 8

Does myosin II have a high or low duty ratio?

Answer 8

Low

Question 9

What forms the core of myosin filaments?

Answer 9

interaction of coiled-coil domains

Question 10

When muscle contraction occurs what happens to the length of the sarcomere?

Answer 10

It gets shorter

Question 11

When muscle contraction occurs what happens to the size of the dark band?

Answer 11

It remains the same

Question 12

Are the 2 heads of myosin independent?

Answer 12

Yes

Question 13

When does the pre-stroke position occur in myosin II?

Answer 13

Once ATP hydrolysis has occurred

Question 14

Does myosin II move hand-over-hand?

Answer 14

No as the heads are independent from each other

Question 15

How many ATP are consumed per step on myosin II?

Answer 15

1

Question 16

What is the purpose of CapZ?

Answer 16

Protects the plus ends of actin filaments

Question 17

What is the role of Z-discs?

Answer 17

In muscle hold plus ends of actin filaments coming from adjacent sarcomeres

Question 18

What is the function of alpha-actinin?

Answer 18

In muscle helps to attach actin filaments to the Z-lines

Question 19

What is the function of tropomodulin?

Answer 19

• Binds and caps minus ends of actin
• Helps regulate length of actin filaments

Question 20

How does tropomodulin help regulate actin filament length?

Answer 20

By blocking dissociation of ADP-bound actin monomers for minus end

Question 21

Which protein acts as a molecular ruler to set the length of actin filaments?

Answer 21

Nebulin

Question 22

What is the largest known protein?

Answer 22

Titin

Question 23

What is the function of Titin?

Answer 23

Functions as a passive molecular spring responsible for muscle elasticity

Question 24

What is the function of tropomyocin?

Answer 24

Controls the binding of myosin

Question 25

What does troponin bind?

Answer 25

Ca²⁺

Question 26

How do troponin and Ca²⁺ regulate muscle contraction?

Answer 26

• Ca2+ triggers muscle contraction
• Ca2+ binds to troponon which shifts conformation and moves tropomyosin, exposing myosin binding sites