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BIOL1412 02 14 2014.docx

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University of Manitoba
Biological Sciences
BIOL 1412
Paul Messing

BIOL1412 02 14 2014 Molecular Basis of Skel. M. Contraction Steps: C) Contraction (mech.) - Sliding Filament Mech. 8) ATP attaches to myosin head, causing its release from actin + unpivot = Recovery Stroke (Fig. 9.12) 9) Myosin head reactivates (ATP ⇒ ADP +Pi) 10) If Ca+2 in cytosol remains high these steps continue ⇒ cycle repeats many times to shorten the sacromere (Fig. 9.6) (Fig. 9.7) Sliding Filament Mech. - Sacromere 1) Sacromere shorten (Fig. 9.6) - H-zone, I-band shorten - A-band = same length 2) Myofibrils shorten: - muscle shortens (Fig. 9.2) 3) thins (actin) + thick (myosin) - myofilaments remain the same length Muscle Fiber Relaxation - Steps: 1) ACh broken down by AChE on motor end plate (facing cleft) (Fig. 9.8) ACh ⇒ acetic acid + choline AChE ⇓ ⇓ Krebs Cycle recycled (as Acetyl CoA) 2) Sacro. Reticulum (SR) actively takes up Ca+2 (Ca+2 -ATPase) 3) Tropomyosin covers myosin binding sites on actin 4) ATP binds to and releases myosin heads (Fig. 9.12) - ATP necessary for: 1) crossbridge release (ATP not broken down) 2) activation of myosin (ATP ⇒ADP + Pi) 3) pump Ca+2 into SR (Fig. 9.11) 4) fiber Na+/K+ -ATPase activity (Fig. 3.11) ClinicalApplication 1) Botulism - improper canning - Clostridium botulinum - prevent exocytosis ofACh - flacaid paralysis - medical - treat uncontrolled blinking, crossed eyes - cosmetic - Botox (wrinkles, sweating) Muscle Tension = force exerted by a muscle or muscle fibre - determined by # of crossbridges formed - in a fibre, affected by: 1) Frequency of stimulation: a) Single stim. = twitch (not normally occurring) i) 1 stim. ⇒ 1 AP (lasts 1-2 msec.) (similar to Fig. 9.14) ii) (latent period) (~2 msec.) ⇒ excitation - contraction coupling occurring iii) contraction period (10-100 msec.) - ⇑ tension
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