The molecular process that makes muscle contraction possible is
that ATP binds to myosin, which releases the energy needed to make
the muscle contract. In this problem, we will examine the
quantities of energy involved in this process.

**NEED HELP WITH PARTS C, D & E, but all input is
appreaciated**

Part 1

The reaction of ATP hydrolysis catalyzed by myosin (M) occurs in
several steps*:

M + ATP → M·ATP

M·ATP → M·ADP·P_i

M·ADP·P_i → M·ADP + P_i (aq)

M·ADP → M + ADP

* T. Kodama & R.C. Woledge, “Enthalpy Changes for
Intermediate Steps of the ATP Hydrolysis Catalyzed by Myosin
Subfragment-1”, J. Biol. Chem. 254(14), 6382-6836

According to experimental data, the heats of reaction for these
four reactions are -90 kJ/mol, +83 kJ/mol, -88 kJ/mol, and +72
kJ/mol.

a) Based on what you know about chemical bonding (from this class,
from chemistry, and from anywhere else), explain the positive and
negative signs for each of these four reactions. What does a
positive and a negative sign mean, and why is a positive (or
negative) sign expected in each case?

b) Find the total energy released (in kJ/mol) in the overall ATP
hydrolysis reaction.

Part 2

The energy released by this reaction in each muscle fiber,
multiplied by a huge number of muscle fibers, results in the
kinetic energy of your muscles moving.

c) Estimate the kinetic energy of your leg when you are walking at
a normal pace.

d) Using the data from Part 1, estimate the total energy released
by ATP-myosin reactions throughout your entire leg. Explain how you
arrived at this estimate.

Some possibly useful information: Muscle fibers (cells) are
composed of many myofibrils, tubular components measuring 1-2
micrometers in diameter. Each myofibril is divided along its length
into sarcomeres (the basic unit of a muscle, with a single myosin
filament), each of which is about 2 micrometers long. Remember that
“kJ/mol” means kilojoules for every 6.02×10²³ myosin
molecules.

e) Are the results from parts c and d similar? If not, what are
some possible ways to account for the discrepancy?