biochemistry

3. List the main proteins composing the structure of sarcomere & describe the function of each.

4. List the main proteins composing thin & thick filaments & their relationships in skeletal muscles.

5. List the main accessory proteins that play an important role in muscle structure & function. Emphasize the function of dystrophin and related proteins.

6. Outline the biochemical events that occur during one cycle of muscle contraction & list the determinants that lead to relaxation.

7. List the different sources of energy for muscle contraction.

10. ATP, and phosphocreatine

11. Enzymes of glycolysis2) Sarcoplasmic reticulum contains calcium to conduct nerve impulses. The muscle cell is called a muscle fiber with plasma membrane called sarcolemma Many nuclei and mitochondria (sarcosome)

14. Main outline structure of sarcomere

15. Main accessory proteins that play an important role in muscle structure & function Titin Nebulin a-Actinin Desmin Dystrophin Calcineurin Myosin-.binding protein C Functions: Help in relaxation of muscle. Regulate assembly length of actin and filaments Stabilization of actin filaments. Maintaing structure of sarcomeres

16. Dystrophin is a cytoplasmic accessory protein, Function: 1-They connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane. 2- Stabilizaton of membrane during contraction & relaxation

18. Myosin has a fibrous tail consisting of two intertwined helices.

22. Skeletal muscle cannot contribute directly to blood glucose because it does not contain glucose-6-phosphatase.

23. Anaerobic metabolism in skeletal muscle produce Lactate (anaerobic glycolysis) then passes to liver to synthesize glucose, which can then return to muscle (the Cori cycle).

24. In the fed state, most glucose is used to synthesize glycogen

28. Steps in Muscle Contraction (Resting sarcomere) Step 1: Head of myosin hydrolyzes ATP to ADP and Pi to result ADP-Pi- myosin complex (high-energy conformation.) Step 2: (in response to nerve/Ca2+ stimulation) Ca+ binds to troponin exposing active site on actin forming actinomycin complex Then binding to ADP-Pi- myosin complex Step 3: Promotes the release of Pi, which initiates the power stroke (conformational change in myosin heads ), then release of ADP Pulling of crossbridgeactin towards center of sarcomere(shortening )

29. Step 4: Myosin head binds another ATP Forming an actin-myosin-ATP complex. Step 5: (key component of relaxation) Myosin-ATP has a low affinity for actin, and actin is thus released. In step 4: If intracellular levels of ATP drop (eg, after death), ATP does not bind myosin head (step 4 above), and actin does not dissociate, and relaxation (step 5)does not occur.

30. Steps in relaxation Step 1: Ca2+ pumped back into sarcoplasmic reticulumbyCa2+ ATPase Step 2: Release of Ca2+ from troponinC Step 3:Troponin, via interaction with tropomyosin, inhibits further myosin head and F-actin interaction. Step 4: Presence of ATP, myosin head lead to release of F-actin. Step 5: The end of interaction between actin and myosin

31. The role of calcium ions in muscle contraction & relaxation During contraction Sarcolemma depolarization: Spreads to internal T tubule system Ca2+ is released from the SR and from the extracellular space Ca2+ interacts with calmodulin (TpC) and myosin light chain kinase to activate myosin (uncovering of myosin binding sites). Activated calmodulin activates the Myosin/ATPase (kinase) Activated kinase transfers phosphate from ATP to myosin cross bridges Phosphorylated cross bridges interact with actin to produce shortening (contraction)

32. During relaxation: SarcoplasmicCa + + reduced and pumped into the SR by ATP-driven Ca + + pump Troponin and tropomyosin, inhibits myosin head and F-actin interaction (covering of myosin binding sites) , and in the presence of ATP the myosin head detaches from the F-actin. Reference: Harper’s Illustrated Biochemistry Chapter 49:Muscle & the Cytoskeleton