You have used "optical tweezers" to study the mechanics of myosin movement in a newly discovered member of the myosin II subfamily. Your results indicate that each myosin exerts a force of about 3 pN along the length of the actin filament, and displaces the filament by about 10 nm in each cycle of ATP hydrolysis. Assuming that the free-energy change for ATP hydrolysis is -50 kJ/mol under your experimental conditions, what is the efficiency of the myosin motor in converting the free energy to mechanical work? Remember that under a constant force F (in newtons), work (W; in joules) is calculated as W = F × d, where d is displacement (in meters) in the direction of the force. Avogadro's number is approximately 6 × 10²³ molecules/mole. Write down your answer as a percentage with no decimals, e.g. 99%.

Question

Quizplus · Accepted Answer

The work performed by one myosin head in each cycle is: W = F × d = 3 pN × 10 nm = 3 × 10^-20 N.m = 3 × 10^-20 J Multiplying this by Avogadro's number gives 1.8 × 10⁴ J/mol, which is equivalent to 36% of the free-energy change of ATP hydrolysis.

You Have Used "Optical Tweezers" to Study the Mechanics of Myosin