Question

The homeostasis of ATP in a cell is dependent on the maintenance of energy status

that is mainly determined by the ATP to AMP ratio, as well as the maintenance of the

adenine nucleotide pool.

a) What is the biochemical mechanism that prevents the overproduction of ATP by

glycolysis? (4 marks)

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b) By referring to the metabolic pathways for the de novo synthesis of purine

nucleotides, discuss how this biochemical process is regulated by:

i) The availability of cellular resources. (4 marks)

ii) The intracellular levels of adenine and guanine nucleotides. (4 marks)

c) How does the mode of regulation of de novo purine nucleotide synthesis

contribute to homeostasis of the adenine nucleotide pool? (3 marks)

Answer 1

a)The ATP molecules which are produced by the breakdown of glucose should be in an accurate amount.If cells supply of ATP is low,then it would breakdown the glucose as quickly as possible to replenish the ATP molecules.But if the supply of ATP is high or overproduced,then its a very difficult task for the cells to oxidize glucose at a very high speed.As a result of this ATP needs to wait for a long duration.The problem that arises here is that since ATP is an unstable molecule it spontaneously hydrolysis back to ADP.i.e,ATP ends up going waste.

So in order to ensure the correct production of ATP molecule ,regulation in the pathways of each step is required.In glycolysis,pathway regulation is done by an enzyme called as Phosphofructokinase(PFK).Here PFK is regulated by ATP and AMP.

Mechanism in ATP and AMP

• ATP - ATP acts as a negative regulator of PFK,which signalizes that if already there are plenty of ATP in a cell,glycolysis need not have to make more.
• AMP(Adenosine monophosphate)-Its a positive regulator of PFK. When a cell has low ATP,PFK will start pushing more number of ATP out of ADP molecules by converting them to ATP and AMP.So high level of AMP signifies the hunger level of cells for its energy and that glycolysis must run quickly to produce ATP.