Question

Which of the following statements about cross-bridges is false? a. They are composed of myosin. b. They bind to ATP after they detach from actin. c. They contain an ATPase. d. They split ATP before they attach to actin.

Short answer

The question is incorrect as there is no false statement among the given options. All statements (a, b, c, and d) about cross-bridges are true.

Step-by-step solution

Analyzing statement "a"

Cross-bridges are formed by the interaction of myosin and actin during muscle contraction. They are mainly composed of myosin, more specifically, the myosin head. So, statement "a" is true. Step 2: Analyzing statement "b"

Analyzing statement "b"

Once the muscle contraction finishes and cross-bridges need to be detached, myosin heads bind to a new ATP molecule. This causes the cross-bridge to detach from the actin filament. Hence, statement "b" is also true. Step 3: Analyzing statement "c"

Analyzing statement "c"

ATPase is an enzyme that catalyzes the hydrolysis of ATP (adenosine triphosphate) into ADP (adenosine diphosphate) and an inorganic phosphate molecule. The myosin head is also known as the myosin ATPase because it contains an ATPase site. The ATPase activity of myosin powers muscle contraction. Thus, statement "c" is true. Step 4: Analyzing statement "d"

Analyzing statement "d"

Before a cross-bridge can form between myosin and actin, the myosin head first binds to ATP. The ATP is then hydrolyzed to ADP and an inorganic phosphate molecule by ATPase activity. The myosin head remains attached to ADP and inorganic phosphate in a high-energy state until it binds to actin. Therefore, the statement "d" is also true. Since all the statements are true, it means that the given exercise has no false statement. So, the question is incorrect as there is no false statement among the given options.