II. Muscular System (skeletal)

Question 1

A. structure

Answer 1

• sarcomere
• actin and myosin filaments overlap
  each other
• actin is the protein that makes little
  thin lines (ray protein)
• myosin = muscle protein
• actin monomers (single unit), actin
  polymers (repeating units)

Question 2

A. structure
Important abilities of myosin

Answer 2

1) affinity (bound/attracted) for actin (binds myosin binding site)
2) molecular motor, ATP-ase bends
- a molecule that ends with “-ase” =
enzyme
3) opposite orientation of myosin
dimers pulls actin filaments together

Question 3

A. structure
More information

Answer 3

• remember ATP is a important
  energy carrier
• ATP (adenosine triphosphate), ADP
  (adenosine diphosphate)
• to make ATP, you start out with a
  ADP+P, add energy, and that energy
  is used to attach the phosphate
  group to ADP, so now we have ATP
• happens in mitochondrion
• the original energy comes from the
  reaction of glucose+oxygen ->
  carbon dioxide+water
• sun energy bond molecules to make
  sugar
• sugar os a way of storing sunlight

hydrolysis of ATP bends myosin head
- binding of ATP to myosin causes myosin to release actin
- myosin hydrolyzes ATP into ADP+P
- myosin – ADP+P binds actin
- myosin releases ADP+P and
bends (power stroke)

Question 4

B. requires nerve stimulation

Answer 4

1) myosin binding sites on actin blocked by troponin–tropomyosin proteins
2) action potential stimulates sarcoplasmic reticulum to release calcium into sarcomere
3) calcium binds troponin-tropomyosin which shift from myosin binding sites on actin
4) calcium pump ATP-ase pumps, calcium back into sarcoplasmic reticulum
5) once calcium is removed from troponin, tropomyosin covers myosin binding sites on actin, stopping contraction

Question 5

C. Requires ATP

Answer 5

how does the sarcomere know when to contract and how much?
- signal from brain