1.  Describe the thick and thin filaments and how they are arranged within a sarcomere during relaxation.

Thick – myosin filaments with head sticking outward. No heads in bare zone

Thin – globular actin proteins in a double helix with 2 protein filaments called tropomyosin also wrapped around the actin.  Troponin, a 3 polypeptide complex holds the tropomyosin in position so that it blocks the myosin-binding site

2.  During relaxation are thick and thin filaments connected? 

No

3.  What effect does the release of Ca⁺⁺ ions into the sarcoplasm have on the arrangement of the thin filament? 

Ca⁺⁺ attaches to troponin which shifts its’ position so that tropomyosin exposes the myosin-binding sites

4.  Where does ATP attach during contraction? (be specific)

myosin head

5.  What happens to this molecule when ATP is hydrolyzed into ADP and P_i?

Myosin goes from a low-energy form to a high-energy cocked position.

6.  What happens during cross-bridge attachment?

When the myosin-binding site is exposed on actin, the myosin head attaches to actin.

7.  What happens when myosin releases ADP and P_i?  What is this step called?

When myosin releases ADP and P_i, the molecule goes from the high-energy position to the low-energy position which pulls the actin toward the bare zone.

This is called the power stroke.

8.  What happens during cross-bridge detachment?  What causes it?

When a new ATP molecule attaches to the myosin head, it causes the myosin molecules to release its bond from actin.

9.  What is the recovery stroke?

ATP then hydrolyzes which again cause myosin to go into high-energy position and cocks it for position to attach to actin again if the myosin-binding site is exposed.

10.  What is the total effect of the steps described above?

All sarcomeres will decrease in length and entire muscle fiber contracts.