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Animation: Myofilament Contraction
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View the animation below, then complete the quiz to test your knowledge of the concept.

1Each actin filament is composed of
A)a single strand of actin molecules.
B)two strands of actin molecules wrapped together.
C)three strands of actin molecules wrapped together.
D)four strands of actin molecules wrapped together.
E)hundreds of strands of actin molecules wrapped together.

2As actin and myosin filaments slide past each other during muscle contraction,
A)actin filaments shorten, while myosin filaments do not.
B)myosin filaments shorten, while actin filaments do not.
C)either actin or myosin filaments shorten, but not both at the same time.
D)both actin and myosin filaments shorten.
E)neither actin nor myosin filaments shorten.

3Which of the following statements about the "heads" of the myosin molecules is TRUE?
A)they form permanent links with actin filaments
B)they can attach to different sites on the actin filament
C)they straighten the myosin filaments
D)they allow the myosin filaments to wrap around each other
E)none of the above

4Each myosin protein has a globular head that extends outward from the myosin filament.

5Unflexing of the myosin head requires ATP.

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