Question

The muscle contraction cycle consist of the following steps. Select the correct sequence.
A. ATP hydrolysis
B. Detachment of myosin from actin
C. Power stroke
D. Attachment of myosin to actin to form cross-bridge

• A. A, D, C, B
• B. D, A, C, B
• C. A, D, B, C
• D. D, C, A, B

Hint:

Cross-bridge Cycle Order:
1. ATP Hydrolysis (cocks head) [A] $\to$ 2. Cross-bridge Attachment [D] $\to$ 3. Power Stroke (pulls actin) [C] $\to$ 4. ATP Binds & Detaches [B].
Rigor mortis occurs when ATP is absent, preventing detachment (step B).

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the correct sequential order of molecular events during the sliding filament cross-bridge cycle of skeletal muscle contraction.

Step 2: Key Formula or Approach:
The cross-bridge cycle driven by ATP binding and hydrolysis proceeds as follows: ATP Hydrolysis (A) $\rightarrow{}$ Cross-bridge Formation (D) $\rightarrow{}$ Power Stroke (C) $\rightarrow{}$ Cross-bridge Detachment (B)

Step 3: Detailed Explation:

• 1. ATP Hydrolysis (A): Myosin ATPase hydrolyzes ATP bound to the myosin head into ADP and inorganic phosphate ($\text{P}_i$). This energizes and re-cocks the myosin head into a high-energy position.

• 2. Attachment Cross-bridge Formation (D): Activated myosin head binds to exposed myosin-binding sites on actin thin filaments, forming a cross-bridge and releasing $\text{P}_i$.

• 3. Power Stroke (C): Release of $\text{P}_i$ triggers the power stroke: the myosin head pivots and pulls the thin actin filament toward the M-line of the sarcomere, releasing bound ADP.

• 4. Detachment (B): A new ATP molecule binds to the myosin head, causing the myosin head to detach from actin, completing one cycle.

Step 4: Fil Answer:
The correct sequence of muscle contraction cycle events is A, D, C, B.