BI 202 9-28 and 9-29 Notes

BI 202 9-28 and 9-29 Notes - September 28, 2010 a. Thick...

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September 28, 2010 a. Thick filaments a.i. Composed of just one protein: myosin a.ii. Head and arm region are usually referred to as the cross-bridge a.iii. Myosin, at the top, are sites that bind to actin a.iv. Sites on head are ATP binding sites a.v. Head can act as an ATPase, which means it can break down ATP into ADP plus a phosphate a.v.1. A cell would do this to get energy for muscle contraction a.vi. Cross bridge itself binds to actin, can swivel directed by the energy of ATP (back and forth motion), brings actin toward M-line a.vii. Thick filaments are made up of lots of myosin in different directions (pull toward M-line in center of myosin) a.viii. Crossbridge Cycle a.viii.1. Fig. 12.12 a.viii.1.a. Myosin ATPase converts ATP to ADP + a phosphate (an inorganic phosphate) a.viii.1.a.i. ADP and phosphate still bound to crossbridge a.viii.1.a.ii. ATP hydrolyzed causing myosin to go back to normal position a.viii.1.a.iii. Energize the cross bridge (in the “cocked” position)
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a.viii.1.a.iv. When the myosin head as ADP and phosphate bound to it, it has very high affinity for actin (binds very well if it can if tropomyosin is in way, will not bind) a.viii.1.b. Myosin binds to actin (aka “attachment”) a.viii.1.c. Phosphate gets released from the cross bridge a.viii.1.c.i. Cross bridge undergoes conformational change ”Power Stroke” a.viii.1.d. Powerstroke pulls actin toward the center of the sarcomere (M- line); ADP is released a.viii.1.e. New ATP binds to the cross-bridge a.viii.1.e.i. Cross-bridge has much lower affinity for actin a.viii.1.e.i.1. If decrease affinity, crossbridge releases actin and cycle starts all over again (start at step “a” again) a.viii.2. If ran out of ATP, when mitochondria quits making ATP (when in rigor mortis) a.viii.3. Rigor Mortis a.viii.3.a. Muscles in deceased contract a.viii.3.a.i. Cross-bridge cycles start but if no new ATP is stuck in the contracted state a.viii.3.b.
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BI 202 9-28 and 9-29 Notes - September 28, 2010 a. Thick...

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