myosin

Examples of myosin in the following topics:

• ATP and Muscle Contraction

  • ATP is critical for muscle contractions because it breaks the myosin-actin cross-bridge, freeing the myosin for the next contraction.
  • ATP is critical to prepare myosin for binding and to "recharge" the myosin.
  • ATP first binds to myosin, moving it to a high-energy state.
  • Once myosin binds to the actin, the Pi is released, and the myosin undergoes a conformational change to a lower energy state.
  • ATP then binds to myosin, moving the myosin to its high-energy state, releasing the myosin head from the actin active site.

• Regulatory Proteins

  • Tropomyosin and troponin prevent myosin from binding to actin while the muscle is in a resting state.
  • The binding of the myosin heads to the muscle actin is a highly-regulated process.
  • When a muscle is in a resting state, actin and myosin are separated.
  • To keep actin from binding to the active site on myosin, regulatory proteins block the molecular binding sites.
  • Describe how calcium, tropomyosin, and the troponin complex regulate the binding of actin by myosin

• Sliding Filament Model of Contraction

  • Actin myofilaments attach directly to the Z-lines, whereas myosin myofilaments attach via titin molecules.
  • The I-band is spanned by the titin molecule connecting the Z-line with a myosin filament.
  • Titin molecules connect the Z-line with the M-line and provide a scaffold for myosin myofilaments.
  • During contraction myosin ratchets along actin myofilaments compressing the I and H bands.
  • The A-band remains constant throughout as the length of the myosin myofilaments does not change.

• Control of Muscle Tension

  • The number of cross-bridges formed between actin and myosin determine the amount of tension that a muscle fiber can produce.
  • Cross-bridges can only form where thick and thin filaments overlap, allowing myosin to bind to actin.
  • If more cross-bridges are formed, more myosin will pull on actin and more tension will be produced.
  • This results in fewer myosin heads pulling on actin and less muscle tension.
  • Because myosin heads form cross-bridges, actin will not bind to myosin in this zone, reducing the tension produced by the myofiber.

• Skeletal Muscle Fibers

  • Skeletal muscles are composed of striated subunits called sarcomeres, which are composed of the myofilaments actin and myosin.
  • Myofibrils are composed of long myofilaments of actin, myosin, and other associated proteins.
  • Within the sarcomere actin and myosin, myofilaments are interlaced with each other and slide over each other via the sliding filament model of contraction.
  • Thick filaments are composed primarily of myosin proteins, the tails of which bind together leaving the heads exposed to the interlaced thin filaments.
  • The molecular model of contraction which describes the interaction between actin and myosin myofilaments is called the cross-bridge cycle.

• Microfilaments

  • Actin is powered by ATP to assemble its filamentous form, which serves as a track for the movement of a motor protein called myosin.
  • Actin and myosin are plentiful in muscle cells.
  • When your actin and myosin filaments slide past each other, your muscles contract.

• Muscle Tissues and Nervous Tissues

  • Skeletal muscle has striations across its cells caused by the arrangement of the contractile proteins, actin and myosin, that run throughout the muscle fiber .
  • Skeletal muscle cells can contract by the attachment of myosin to actin filaments in the muscle, which then ratchets the actin filaments toward the center of the cells.

• Intermediate Filaments and Microtubules

  • Intermediate filaments have an average diameter of 10 nanometers, which is between that of 7 nm actin (microfilaments), and that of 25 nm microtubules, although they were initially designated 'intermediate' because their average diameter is between those of narrower microfilaments (actin) and wider myosin filaments found in muscle cells.

• Structure and Function of the Muscular System

  • Muscle cells, or myocytes, contain myofibrils comprised of actin and myosin myofilaments which slide past each other producing tension that changes the shape of the myocyte.

• Types and Functions of Proteins

  • Actin and myosin allow muscles to contract, while albumin nourishes the early development of an embryo or a seedling.