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bioch. q - raheem
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03-08-2011, 06:46 PM
Which of the following statements about the contraction of skeletal muscle is correct? a) The power stroke of skeletal muscle contraction occurs when the myosin head hydrolyses ATP. b) The power stroke of skeletal muscle contraction occurs when the myosin head binds ATP. c) The power stroke of skeletal muscle contraction occurs when the myosin head releases ATP. d) The power stroke of skeletal muscle contraction occurs when the myosin head releases ADP and Pi.
03-08-2011, 06:55 PM
GOOD
Which of the following statements about the contraction of skeletal muscle is correct? Your Answer: d) The power stroke of skeletal muscle contraction occurs when the myosin head releases ADP and Pi. Feedback: Skeletal muscle cells are made up of a regular arrangement of thick (myosin) and thin (actin) filaments. The latter are anchored to Z discs (proteins) at their plus (+) end. Thick filaments form rigid rods, each terminating in a globular head perpendicular to the thin filaments. During contraction thick filaments move the thin filaments by means of a ratchet mechanism pulling the thin filaments and their attached Z discs towards the centre of the thick filament. A myosin head cannot bind to actin (relaxed state) when ATP is bound to it. When ATP is hydrolysed (myosin head is an ATPase) a conformational change occurs. A force is exerted by the myosin on the actin filament. This is the primed state (the ADP and Pi remain attached to the head). The myosin head can now bind to the actin filament if Ca+2 is present. ADP and Pi are released liberating energy and forcing the thin filament to slide causing a contractile force. This is the power stroke. Page reference: Page 128 |
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