- The sarcoplasmic reticulum releases calcium ions that bind to the troponin complex. The binding of calcium ions to troponin results in a change in the position of tropomyosin. The shift of the tropomyosin strand exposes the myosin binding sites of the actin filament so that muscular contraction can occur.

- The diagram to the left depicts the model for muscular contraction. - The myosin head bound to ATP is in its low-energy configuration (shown in the upper left-hand corner of the diagram). - When ATP is hydrolyzed, the myosin head pulls back into its high-energy configuration. - The myosin head then forms a cross-bridge with the actin filament. When ADP + Pi is released, the myosin head returns to its low-energy state and shifts the actin filament. The cycle continues when another molecule of ATP binds to the myosin head.

The strength of a contraction depends upon the

- number of units contracted. - number of cross bridges that participate in the power stroke. - availability of ATP.

Sustained muscle contraction is caused by

- repeated interactions of the myosin and actin of the contracting units.

The energy necessary for muscle contraction comes from

- ATP bound to the myosin heads

The attachment of the myosin head to the actin filament causes

- the actin filament to slide to its contracted position as the myosin head returns to its original position.

Simultaneous to Ca2+ binding to tropomyosin and exposing binding sites on actin,

- ATP is hydrolized into ADP + Pi causing the myosin head to move into a high energy position.

12.15.3 The Sliding Filament: Interaction of ATP, Actin, Myosin, and Calcium Flashcards by Irina Soloshenko

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12.15.3 The Sliding Filament: Interaction of ATP, Actin, Myosin, and Calcium Flashcards

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