Biology, Eighth Edition (Raven)

Chapter 47: The Musculoskeletal System

Breakdown of ATP and Cross-Bridge Movement During Muscle Contraction

What is the pathway of energy transfer during muscle movement? The contraction of skeletal muscles is one of the most energetically expensive activities that the body does on a regular basis. Adenosine triphosphate (ATP) is split into adenosine diphosphate (ADP) and phosphate to supply the energy for muscle contraction. The free energy released by the ATP when the phosphate is split off is transferred to the heads on the myosin filaments. The heads move and store potential energy in their new position. When the heads interact with actin, the energy is used to slide the filaments past one another transferring the energy into movement (kinetic energy).

View the animation below, then complete the quiz to test your knowledge of the concept.


During contraction of a muscle, calcium ions bind to...
A)the actin myofilament.
B)the troponin molecule.
C)the tropomyosin molecule.
D)the sarcoplasmic reticulum.
E)the sarcolemma.

The bond between the actin and myosin head is broken when...
A)an ATP molecule binds to the myosin head.
B)an ATP molecule binds to the actin molecule.
C)an ATP molecule breaks down on the myosin head.
D)an ATP molecule breaks down on the actin molecule.
E)ADP and phosphate bind to the myosin head.

Energy is released when...
A)ADP is broken down into ATP and phosphate.
B)ATP is broken down into ADP and phosphate.
C)ADP and phosphate combine to form ATP.
D)ATP and phosphate combine to form ADP.
E)AMP and two phosphates combine to form ATP.

The sequence of cross bridge formation and myofilament movement will be repeated as long as calcium ions are present.

When cross bridges form and the muscle fibers contract, the actin myofilament slides past the myosin myofilament.
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