Muscle contractions are caused by the motor protein myosin which consumes the hi

Question

Muscle contractions are caused by the motor protein myosin which consumes the high energy molecule ATP for fuel. The ATP molecules carry a negative charge of 4e, so the active site of the myosin has a positive charge to help the ATP find the correct place to bind.

Consider the following arrangement of an ATP molecule, a myosin binding site (q = +3), a RNA molecule with a charge 150e, and a protein carrying a charge 6e. Since these molecules are immersed in water, the dielectric constant is K = 80. Calculate:

a) The electric potential at the ATP molecule

Explanation / Answer

a) V = sum of kq/r

= 9.0E9*1.6E-19*(6/5.0E-9+3/3.0E-9 -150/200.0E-9)=2.088 V

b) sum forces in the x
Fx = 9.0E9*1.6E-19^2*(-4*3/3.0E-9^2 -150*4/200.0E-9^2 -6*4/5.0E-9^2*3/5)=-4.43 E-10 N

Fy=9.0E9*1.6E-19^2*6*4/5.0E-9^2*4/5=1.77E-10 N

so <-0.443, 0.177 > nN

c) E = q dV = 4.0E-9*2.088=8.35E-9 J per ATP

so 8.35E-9*6.0233E23=5.03E15 J per mole = 1.2E12 kCal/mole

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