lecture 10 sample problem answers

8/18/2019 Lecture 10 Sample Problem Answers

1/3

Biosc 1000

Page 1 of 3

Lecture 10 Sample Problem Answers

1. If the !G of the reaction of A"B is -12.5 kJ/mol, what predictions can we makeabout the direction of the reaction and the equilibrium?

If the free energy of the reaction of A! B is -12.5kJ/mol, then the reaction isthermodynamically favorable (because !G


2/3

Biosc 1000

Page 2 of 3

3. Under biologic standard conditions, the free energy of hydrolysis of L-glycerol

phosphate is -9.2 kJ/mol and for ATP hydrolysis is -30.5 kJ /mol. Show that when ATPis used as a phosphoryl donor for the formation of L-glycerol phosphate, the value of the

equilibrium constant is altered by more that 105.

Given !G= -9.2kJ/mol for hydrolysis of L-glycerol phosphate

Therefore, !G = + 9.2kJ/mol for phophorylation of L-glycerol

And !G= -30.5kJ/mol for hydrolysis of ATP

!G= -RTlnK ; where R= 8.31 x 10-3 kJ/(mol x K) and T= 310 K

Not coupled to ATP hydrolysis:

!G= -RTlnK

+9.2 = -2.58 ln K

K= e9.2/-2.58

K = e-3.56

K = 0.028 = 2.8 x 10-2

Coupled to ATP hydrolysis:

!G= -RTlnK

+9.2 + (-30.5) = -2.58 lnK

K= e-21.3/-2.58

K= e8.25

K= 3849.9 = 3.8 x 103


3/3

Biosc 1000

Page 3 of 3

4. Many important reactions are “driven to completion” by the hydrolysis of pyrophosphate (such as the attachment of amino acids to tRNA). Yet, the standard free

energy of hydrolysis for pyrophosphate is only -19.3 kJ/mol, a rather low value among

phosphoryl transfer agents. Why should a reaction with such a small !G°# be used in

critically important reactions?

Hydrolysis of pyrophosphate “drives a reaction to completion” by removing the product of the reaction, thus preventing accumulation of reaction product and

making ATP hydrolysis irreversible.

lecture 10 sample problem answers

Documents