Question

If a cell capable of de noto synthesis of purine nucleotides has adequate AMP but is deficient in GMP, how would the cell regulate synthesis to increase [GMP]? If both AMP and GMP were present in appropriate concentrations, what would happen?

Short answer

Answer: In a cell with adequate AMP and deficient GMP, AMP inhibits the enzyme adenylosuccinate synthetase, preventing further synthesis of AMP. The deficiency of GMP activates IMP dehydrogenase and GMP synthetase, leading to an increased production of GMP. When both AMP and GMP are present in the appropriate concentrations, they provide a balanced feedback inhibition on their respective synthesis pathways, maintaining an optimal balance of purine nucleotides needed for various cellular processes.

Step-by-step solution

Understand purine nucleotide synthesis

Purine nucleotides, such as AMP and GMP, are synthesized in a pathway called de novo purine nucleotide synthesis. This pathway involves a series of enzyme-catalyzed reactions that lead to the formation of Inosine monophosphate (IMP), which is a common precursor for both AMP and GMP. IMP can be then converted into AMP or GMP via specific enzymatic reactions.

Explain the regulation of purine nucleotide synthesis in the presence of adequate AMP and deficient GMP

The cell regulates purine nucleotide synthesis through feedback inhibition by the end products of the pathway. When a cell has adequate AMP but deficient GMP, AMP will inhibit the enzyme adenylosuccinate synthetase, which is responsible for the conversion of IMP to AMP. This prevents further production of AMP. On the other hand, the deficiency of GMP leads to the activation of IMP dehydrogenase, which converts IMP to xanthosine monophosphate (XMP), and GMP synthetase, which further converts XMP to GMP. As a result, the cell increases the production of GMP to maintain a balance between AMP and GMP concentrations.

Describe the regulation of synthesis when both AMP and GMP are present in appropriate concentrations

When both AMP and GMP are present in appropriate concentrations, they will provide a balanced feedback inhibition on their respective synthesis pathways. AMP will inhibit adenylosuccinate synthetase, and GMP will inhibit IMP dehydrogenase and GMP synthetase. This ensures that the cell maintains an appropriate balance of both purine nucleotides, essential for various cellular processes like DNA and RNA synthesis, energy production, and signaling.