MUSCLE CONTRACTION BIOCHEMISTRY – Dr. Block Flashcards
Name 3 types of muscle and tell which are striated. What does striated mean? Which are voluntary and which are involuntary?
Skeletal – striated and voluntary
Cardiac – striated and involuntary
Smooth – not striated and involuntary
Striated muscles are enclosed by a membrane known as the sarcolemma that can be excited by electrical impulses from nerves. .
What is the composition of the thick filaments in the sarcomeres?
Protein myosin and make up A-bands/thick filaments.
What is the composition of the thin filaments in the sarcomeres?
Actin, tropomyosin and troponin make up I-bands/thin-filaments
Which kinds of filaments lie in which bands of the sarcomeres?
A-bands have thick filaments with the H-zone in center, I-bands have thin filaments with the Z-line in center.
Describe the structure of myosin. Does it have any enzymatic activity? If so, what kind?
Myosin is a fibrous protein consisting of 2 intertwined helices with a globular head region attached at one end on each. The protein is a 460kD hexane containing one pair of heavy chains (200kD) and 2 pairs of light chains (15 & 27 kD).
Myosin has ATPase activity and binds to the insoluble F-actin protein in skeletal muscle.
Briefly describe the mechanism of muscle contraction.
The mechanism is based on the attachment to Myosin to F-actin and powered by ATP.
Myosin head hydrolyzes ATP to ADP and Pi, but does not release them. Myosin with ADP and Pi binds to F-actin at a 90 degree angle. Binding promotes ADP and Pi are to be released, causing the myosin head to rotate to 45 degrees. A new ATP binds to the myosin-F-actin complex. However, due to a low affinity of ATP-myosin for actin, the myosin-ATP complex is released from F-actin.
Describe the 3 peptides of troponin and what function they perform. Where are troponin and tropomyosin in muscle?
Troponin has 3 peptides:
=> Troponin T (Tpt) – binds to tropomyosin and other Tp units.
=> Troponin I (TpI) – inhibits F-actin-Myosin interaction and binds other Tp units.
=> Troponin C (TpC) – binds 4 Ca2+ molecule (like calmodulin).
Tropomyosin is found in the thin filaments of all muscle. Troponin is found only in thin filaments of striated muscle, and has 3
What divalent ion plays a crucial regulatory role in muscle contraction and what does it bind to in striated muscle?
Ca2+ plays a crucial regulatory role in muscle contraction. In striated muscle, Ca2+ binds to TpC, which changes the interaction of TpI and TpT with F-actin, allowing the myosin head-Adp-Pi to interact with F-actin.
In smooth muscle, a chelate is formed with calcium-tropomyosin-actin complex and the phosphate on the light chain. This increases crossbridges between myosin heads and actin. It is the binding of calmodulin-4-Ca that phosphorylates the p-light chain that ceases to inhibit the myosin-F-actin cycle.
binding of what to G-actin makes F-actin?
Mg2+
Myosin can be cleaved by what to form light and heavy meromyosin? Which of these is cleaved to form HMMS-1 and HMMs-2?
Myosin can be cleaved by trypsin to form light and heavy meromyosin. Heavy meromyosin is cleaved by papain to hen form HMMs-1 and HMMs2, of which HMMS-1 holds the head group with ATPase and binds F-actin.
