Question

QUESTION 42 of citric acid builds up in a respiring cell what effect does this have on respiration? Is this a positive or negative form of feedback regulation? Explain specifically how citric acid regulates the pathways (think about the enzymes involved). Why is this regulation of respiration advantageous for the cell? TTTT Paragraph Arial 3 (12) - E.T. DOQE TT,

Answer 1

Citric acid is involved in regulating the respiration, by acting on the enzymes involved in the multiple ways:

• Citric acid regulates the phosphofructokinase(PFK) enzyme when in excess, to inhibit or slow down glycolysis. It does the same by binding to the allosteric site of the enzyme. This is a negative feedback regulation to stop the influx into the TCA cycle from glycolysis.

• In higher concentration, citrate can also allosterically bind the citrate synthase enzyme (responsible for forming citrate from oxaloacetate and acetyl-CoA) and inhibit its activity. This is an example of negative feedback regulation of TCA cycle, due to energy changes.

• If the citrate concentration exceeds more than that required for energy production by TCA cycle, it is transported to cytoplasm to be converted to acetyl-CoA and Oxaloacetate by Citrate lyase. This then promotes the glucogenic pathway.

Hence, if Citric acid builds up, it will inhibit glycolysis and TCA cycle required for more energy production but It will activate gluconeogenesis and energy storage in the form of glycogen.

Advantage of this regulation for the cell:

This helps in the maintenance of the energy balance in the cell.

When there's ample amount of energy in the cell (more ATP) and citric acid is in excess. It acts to stop the energy-yielding processes like Glycolysis and TCA cycle.

On the other hand, when the energy is needed in the cell (lesser ATP than required), citric acid gets utilized in the TCA cycle for generating more reducing power and hence, fulfilling energy needs.