Bioenergetics

Question 1

Discuss what the change in free energy is and how we calculate it

Answer 1

This is the energy available to do useful work at constant pressure and temperature, and is defined as

ΔG = ΔH-TΔS

ΔH = change in enthalpy (heat constant)
ΔS = change in Entropy
T = Temperature in kelvins

Question 2

For a biochemical reaction, the change in free energy can be used to predict the direction in which the reaction will proceed (but not the speed, that is enzyme stuff)

For the reaction:
aA + bB = cC + dD

what is our free energy, and based on the value, how will the reaction proceed?

Answer 2

ΔG = ΔG0’ + RTln ([C]^c * [D]^d) / ([A]^a * [B]^b)

ΔG0' = Standard free energy change at pH 7 (ignoring the concentration of water)
ΔG = negative means the reaction will proceed for the release of energy.

Question 3

If ΔG = 0, meaning we are at equilibrium, how does our formula of ΔG = ΔG0’ + RTln ([C]^c * [D]^d) / ([A]^a * [B]^b) change and in addition, what is Keq?

Answer 3

ΔG = ΔG0’ + RTln ([C]^c * [D]^d) / ([A]^a * [B]^b), when ΔG = ΔG = 0 simply becomes
ΔG0’ = - RTln ([C]^c * [D]^d) / ([A]^a * [B]^b)

Keq = the equilibrium constant, and is related to the concentrations of the substances and products at equilibrium

Keq = ([C]^c * [D]^d) / ([A]^a * [B]^b)

Therefore at equilibrium, Keq > 1 means ΔG0’ is negative, meaning the reaction is more likely to proceed spontaneously

Question 4

Enzyme effects on Keq

Answer 4

NONE