Muscle cell structures - actin, myosin and titin filaments
Once the muscle cell has been excited it will contract. • A muscle action potential will trigger the release Of Ca2+ ions into the sarcoplasm. • The Ca2+ ions bind to the regulatory proteins and trigger contraction. • Within skeletal muscle cells are structures that provide the ability to contract forcefully. • Myofibrils: rod-like structures that extend the length of the cell and contain repeating units called sarcomeres. • Sarcomeres: contractile units of a skeletal muscle cell that contain actin (thin) and myosin (thick) filaments. • When these filaments move over each other, the muscle cell contracts. ☆ Muscle cell structures - actin filament • The actin filament consists of actin proteins and regulatory proteins. • The actin protein has binding sites for myosin molecules. • The regulatory protein, tropomyosin, is wrapped around the actin molecules, covering the myosin binding sites. • A second regulatory protein, troponin, contains binding sites for Ca2+ ions and is attached to actin and tropomyosin. • In the presence of Ca2+ ions, troponin binds with calcium and pulls the tropomyosin away from the myosin binding sites and uncovers them. ☆ Muscle cell structures - myosin filament • The myosin filament consists of myosin molecules, each with a head (or crossbridge) and tail. • ATP binds to the crossbridge. • When ATP binds with myosin it is hydrolyzed, releasing energ to move the myosin protein. • Myosin crossbridges attach to specific myosin binding areas. • When the actin and myosin binds, any movement of the myosin filament will also move the actin filament. ☆Muscle cell structures - titin filament •The elastic titin filament allows the sarcomere to return to its resting length after contracting or stretching. Category
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