Muscular System: Cross Bridge Cycling Interactive Physiology (Pearson)

Muscular System: Cross Bridge Cycling


1. What structure has binding sites for ATP?

- Myosin


2. What is the name of the narrow region in the center of the A band where only thick filaments
are present?
- H zone is the name

3. What structures mark the ends of a sarcomere?

- Z discs mark the ends of a sarcomere.

4. What structures can powerfully pull the thin filament over the thick filament in the sliding
filament mechanism during muscle contraction?

- Myosin cross-bridges

5. The myosin heads have binding sites for what two important components of cross bridge
cycling?

- Actin filaments and the initiation of the sliding filaments

6. What causes the re-positioning of the myosin head to its high-energy conformation?

- The hydrolysis of ATP which results in the re-energization and repositioning of the
Myosin head.

7. What step of the cross bridge cycle is triggered when the inorganic phosphate detaches from
the myosin head?

- The bound ATP linked to the myosin is hydrolyzed to ADP and inorganic phosphate
in the last phase of cross-bridge cycling. The myosin head returns to its energetic,
cocked state.

8. What molecule provides the energy for the cross bridge cycle?

- Adenosine Triphosphate (ATP)

9. In which step of the cross bridge cycle does the myosin head pivot and move the thin
filament?

- ADP and P are released and the myosin head pivots and bends, transforming into a
low energy bent state and as a result it attracts the actin filament to the M line.

10. What ions need to be removed from the sarcoplasm for muscle relaxation to occur?