Sarcomere A-band H-zone Thin filament (actin) Thlck fillament (myosin) Z-llne -band ATP binds to myosin head. Actin-binding slte on myosin releases from actin. ADP Is released. ADP АТР Actin-blnding site dloses followed by Muscle contractlon H,0- power stroke as myosin head retracts. ATP hydrolysls. Myosin head "cocks." API P,release results In strong blnding of myosin head to actin. Weak binding of myosin head to actin. A FIGURE 7.48 A model of the ATP cycle in muscle contraction. For clarity, only one of the two myosin headpieces is shown going through a binding, power stroke, and release cycle. The second myosin head- piece is shown in light green. The individual steps of the cycle are described in the text.
A few hours after the death of an animal, the corpse will stiffen as a result of continued contraction of muscle tissue (this state is called rigor mortis). This phenomenon is the result of the loss of ATP production in muscle tissue.
(a) Consult as shown and describe, in terms of the six-step model of muscle contraction, how a lack of ATP in sarcomeres would result in rigor mortis.
(b) The Ca2+ transporter in sarcomeres that keeps the [Ca2+]∼10-7 M
requires ATP to drive transport of Ca2+ ions across the membrane of the
sarcoplasmic reticulum. How would a loss of this Ca2+ transport function
result in the initiation of rigor mortis?
(c) Rigor mortis is maximal at ∼12 hrs after death and by 72 hrs is no
longer observed. Propose an explanation for the disappearance of rigor
mortis after 12 hrs.
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