Muscle calcium and the biochemistry of actin -myosin crosslinking for contraction by striated muscle of invertebrate animals.
This scene shows the events that activate muscle contraction and the and sliding of the actin filaments by the myosin heads. the cycle starts when an electrical impulse from a motor neuron motor neurons that control the contraction of a single muscle fiber, and each motor neuron has multiple end plate junctions the nerve signal from a motor neuron does not generate an action
Potential in an the electrical depolarization also spreads into tiny membranous invaginations of the fiber membrane called transverse tubules, or t-tubules. the t-tubules align with the a-band in invertebrate muscles. the t-tubules essentially carry the electrical signal into the sarcoplasm depolarization of the t-tube membrane activates calcium the released calcium then
Initiates the muscle contraction calcium-activated troponin causes a conformational shift in the protein tropomyosin which winds around the actin helix and blocks the myosin binding sites on the actin molecules, this frees the actin molecules to bind the myosin head units. an enzyme that splits the high energy phosphate bond of atp to produce adenosine diphosphate (adp)
And inorganic phosphate. the resulting adp and inorganic phosphate remain associated with the myosin head which is also charged with the energy released by the to start the contraction cycle, the myosin head attaches loosely to actin, then releases the inorganic phosphate which causes tight binding with the actin. after tight binding, proteins in the myosin head undergo
A conformational change that results in repositioning the angle of attachment between the myosin head and the actin. the shift to the new conformation pulls the actin along the myosin. after pulling the actin, myosin exchanges adp for a new molecule of atp. this results in a release of the myosin head from the actin. the myosin head resumes its relaxed conformation and position,
Transcribed from video
5. Calcium and the Biochemistry of Muscle Contraction (Invertebrate) By Larry Keeley