A typical relaxed sarcomere is about 2.3 μm in length and contracts to about2 μm in length. Within the sarcomere, the thin filaments are about 1 μmlong and the thick filaments are about 1.5 μm long.(a) Describe the overlap of thick and thin filaments in the relaxed and contracted sarcomere.(b) An individual “step” by a myosin head in one cycle pulls the thin filamentabout 15 nm. How many steps must each actin fiber make in one contraction?

Which of these events occurs during the team phase, just when a muscle has been stimulated? a) Ca2 + binds to troponin b) ATP is broken down into ADP c) active transport of Ca2 + into the sarcoplamate reticle d) sarcomeres are abbreviated

Z1

Place these structures in order from LARGEST structure to SMALLEST: A) Myofibril  B) Myofilament (MYOSIN) 1 C) Muscle Body D) Muscle Bundle (Fascicle) E) Muscle Fiber F) Myofilament (ACTIN)

15) what role does calcium play in muscle contraction? a) calcium is not involved in skeletal muscle contraction  b) it binds to tropomyosin and moves Tripp in away from the myosin binding sit on the actin molecules  c) it's binds to Troponin and moves tropomyosin away from the actin binding sit on the myosin molecules d) it binds to troponin and moves tropomyosin away from the myosin binding site on the actin mole

Give typed explanation  Put the events of a single cross-bridge cycle in the proper order. Start with Calcium is released from the sarcoplasmic reticulum.   a) myosin binds to actin   b) ATP binds to myosin, cross-bridge disconnect   c) ATP splits into ADP and Pi   d) Myosin head re-energized, repositions into high energy state   e) Calcium resequestered into sarcoplasmic reticulum   f) Cross-bridge power stroke   g) Calcium binds to troponin , and actin binding sites are exposed

2 a) What does calcium do in a skeletal muscle cell and where in the cell does it come from?                   b) John’s Stetson (his hat) blew off his head in a strong wind and he sprinted down the hill to retrieve it.  Where did his ATP come from in the first 6 seconds and the next 8 seconds of his run?

Describe the movement of myosin along an actin filament. Outline the primary molecular steps and explain how this process is used by cells. How many actin monomers within an actin filament would a myosin molecule need to ratchet in order to contract a cell by approximately 1 um? How fast could a non-muscle cell make this contraction compared to a muscle cell if the relative rates of myosin walks on F-actin are 4.5 um/sec and 0.04 um/sec for myosin II and I respectively?

Cofilin preferentially binds to older actin filamentsand promotes their disassembly. How does cofilin distin-guish old filaments from new ones?

When a muscle fiber is stimulated with repeated stimuli, the contraction force is summed due to: a) an increasing number of engine units recruit b) the number of actin / myosin bonds decreases c) increased strength of the action potential in the plasma membrane d) The Ca2 + concentration around and in the myofibrils increases