Lecture 11: special role of ATP

Question 1

What is the principles of coupled reactions.

Answer 1

Anabolic reactions (to build stuff) require energy input to be favourable. This energy comes from the coupling the anabolic reaction to the hydrolysis of ATP-> ADP + Pi. This allows the standard ΔG’ of both reactions to be added together and make an overall negative ΔG’.

Question 2

What are the reasons energy is released from ATP

Answer 2

1. Resonance stabilisation of free phosphate is better than for triphosphate
2. Electrostatic repulsion of triphosphate is more energetically unfavourable than biphosphate
3. Water can more effectively hydrate free phosphate t

Question 3

What are the reasons energy is released from hydrolysis of ATP + H20 going to ADP + Pi

Answer 3

1. Resonance stabilisation of free phosphate is better than for triphosphate
2. Electrostatic repulsion of triphosphate is more energetically unfavourable than biphosphate
3. Water can more effectively hydrate free phosphate than triphosphate (strength of H bonds with ADP +Pi is stronger than with ATP)

Question 4

What is the difference between spontaneity of a reaction and the equilibrium constant of a reaction and the rate of a reaction

Answer 4

Spontaneity: refers to whether ΔG’ is negative or not. Just whether it is energetically favourable. No effect on Rate.

Rate: the speed at which the reaction proceeds/ products made. (can be increased by enzymes)

Equilibrium constant: is the ratio of products to reactants when the system is at equilibrium. Kind of which reaction is favoured. So this is linked to ΔG in that a large Keq means that forward reaction is favoured- this means its energetically good.

Question 5

What is the difference between spontaneity of a reaction and the equilibrium constant of a reaction

Answer 5

Spontaneity: refers to whether ΔG’ is negative or not. Just whether it is energetically favourable.

Equilibrium constant: is the ratio of products to reactants when the system is at equilibrium. Kind of which reaction is favoured. So this is linked to ΔG in that a large Keq means that forward reaction is favoured- this means its energetically good.

Question 6

Does ΔG affect the rate of a reaction

Answer 6

NO. Rate: the speed at which the reaction proceeds/ products made. (can be increased by enzymes) but ΔG is simply which reaction is favoured to start

Question 7

What is ΔG at equilibrium

Answer 7

0

Question 8

What do the Keq values tell us about the energetic favourabilty of a reaction from this ΔG’=-RT ln Keq

Answer 8

If the Keq are large (Keq>0) then the ΔG will be negative = hence SPontaneous

If the Keq is small (Keq <0) then the ΔG will be positive = hence unfavourable

Question 9

How does the coupling of ATP hydrolysis affect the equlibria of the reaction

Answer 9

It shifts the equilibrium point to favour the forward reaction but only enzymes will accelerate the pace towards equilibrium