Question

a&p flix activity: the cross bridge cycle
2 parts | 0.5 of 1 point

place the steps that occur during a single cross bridge cycle in the correct order from left to right.

show instructions

• adp is released and myosin slides the thin filament toward the center of the sarcomere.
• atp binds to the myosin head and detaches it from actin.
• the activated myosin head binds to actin, forming a cross bridge.
• atp is hydrolyzed to adp and \\(p_i\\) and the energy released re-cocks the myosin head.

atp hydrolysis activates the myosin head
cycle repeats

Explanation:

🆕 New Concept Discovered: Cross-Bridge Cycling
How muscles contract at the molecular level

Step 1: Identify the starting point

The diagram provides a hint at the beginning of the sequence: "ATP hydrolysis activates the myosin head".

ATP hydrolysis splits ATP into ADP and inorganic phosphate (\(\text{P}_i\)), which transfers energy to the myosin head, putting it into a high-energy, "cocked" position.

Therefore, the first step in this sequence is:

• "ATP is hydrolyzed to ADP and \(\text{P}_i\) and the energy released re-cocks the myosin head."

Step 2: Form the cross-bridge

Once the myosin head is energized and "cocked," it is ready to bind to the exposed active sites on the actin (thin) filament. This physical connection between myosin and actin is called a cross-bridge.

Therefore, the second step is:

• "The activated myosin head binds to actin, forming a cross bridge."

Step 3: Execute the power stroke

Once bound, the stored energy is released. ADP and \(\text{P}_i\) are released from the myosin head, causing the head to pivot and bend. This pulling action (the power stroke) slides the thin actin filament toward the center of the sarcomere.

Therefore, the third step is:

• "ADP is released and myosin slides the thin filament toward the center of the sarcomere."

Step 4: Detach the link to reset

To break the link and allow the cycle to repeat, a new molecule of ATP must bind to the myosin head. When ATP binds, the link between myosin and actin weakens, and the myosin head detaches.

Therefore, the fourth step is:

• "ATP binds to the myosin head and detaches it from actin."

---

Answer:

Place the steps in the following order from left to right:

1. ATP is hydrolyzed to ADP and \(\text{P}_i\) and the energy released re-cocks the myosin head.
2. The activated myosin head binds to actin, forming a cross bridge.
3. ADP is released and myosin slides the thin filament toward the center of the sarcomere.
4. ATP binds to the myosin head and detaches it from actin.