BIOL 1030H Lecture Notes - Lecture 3: Myocyte, Oxidative Phosphorylation, Cardiac Muscle
13 May 2018
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Animal Movement
Muscles
• Biological motors that generate force
• Composed of multinucleated muscle fibers
• Use ATP generated through cellular respiration
• Contain contractile proteins (actin and myosin)
Muscles categorized as striated or smooth
Striated - appear striped
• Skeletal and cardiac muscle.
• Actin and myosin arranged in regularly, repeating pattern
Smooth – appear uniform
• Walls of arteries, digestive and excretory systems
• Actin and myosin arranged in irregular pattern
Muscle shortening OVERVIEW
• Interactions between myosin and actin cause muscle fibre to shorten and produce force
• Two heads of the myosin molecules bind to actin at specific sites to form cross-bridges
• Myosin filaments pull actin using cross-bridges
• Key is for myosin filaments to slide is their ability to undergo conformation change
Force and velocity are inversely related
• Muscles shorten fastest when there is little force
• At high contraction velocities, fewer cross-bridges form; reducing force
• Large force production requires slow velocity
Some species have evolved very rapid cross-bridge cycling, but produce little force
Slow twitch fibres
• Develop force more slowly, but resist fatigue
• Energy supplied by oxidative phosphorylation
– Many mitochondria, well supplied with oxygen
– Contain abundant myoglobin (muscle oxygen storage molecule; gives slow twitch fibres a red
colour)
– Express “slow” form of myosin, limiting cross-bridge cycling
Document Summary
Muscles: biological motors that generate force, composed of multinucleated muscle fibers, use atp generated through cellular respiration, contain contractile proteins (actin and myosin) Striated - appear striped: skeletal and cardiac muscle, actin and myosin arranged in regularly, repeating pattern. Smooth appear uniform: walls of arteries, digestive and excretory systems, actin and myosin arranged in irregular pattern. Force and velocity are inversely related: muscles shorten fastest when there is little force, at high contraction velocities, fewer cross-bridges form; reducing force, large force production requires slow velocity. Some species have evolved very rapid cross-bridge cycling, but produce little force. Slow twitch fibres: develop force more slowly, but resist fatigue, energy supplied by oxidative phosphorylation. Contain abundant myoglobin (muscle oxygen storage molecule; gives slow twitch fibres a red colour) Express slow form of myosin, limiting cross-bridge cycling. Fast-twitch fibres: generate more force than slow-twitch fibres, energy supplied by anaerobic glycolysis.
