Q24. The common metabolic precursor of amino acids such as Proline and Glutamine is
1. Oxaloacetate
2. Ribose-5-Phosphate
3. Pyruvate
4. 𝛼-Ketoglutarate

Introduction to Metabolic Precursors of Amino Acids

Amino acids are the building blocks of proteins and play crucial roles in various biochemical processes in living organisms. The synthesis of amino acids involves specific metabolic precursors derived from the citric acid cycle and glycolysis. Understanding the origin of amino acids such as Proline and Glutamine is important for mastering metabolic pathways, especially for students preparing for DBT BET JRF, CSIR NET Life Science, IIT JAM, and GATE Biotechnology.

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Key Phrase: Common Metabolic Precursor of Proline and Glutamine

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Metabolic Pathway of Proline and Glutamine Synthesis

Proline and Glutamine are non-essential amino acids synthesized from intermediates of the citric acid cycle (Krebs cycle). The common metabolic precursor for both Proline and Glutamine is α-Ketoglutarate.

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1. α-Ketoglutarate – The Common Precursor

• α-Ketoglutarate is an intermediate of the citric acid cycle.
• It serves as a nitrogen acceptor and is involved in the transamination reaction leading to the formation of glutamate.
• Proline and Glutamine are both synthesized from glutamate, which is derived from α-Ketoglutarate.

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2. Biosynthesis of Glutamine from α-Ketoglutarate

1. α-Ketoglutarate undergoes transamination to form glutamate.
2. Glutamate is converted to Glutamine through the action of Glutamine Synthetase, which adds an amine group using ATP.

Reaction:

Glutamate + NH3+ATP→Glutamine + ADP + Pi

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3. Biosynthesis of Proline from α-Ketoglutarate

1. Glutamate is reduced to form Glutamic Semialdehyde.
2. Glutamic Semialdehyde then cyclizes and reduces to form Proline.

Reaction:

Glutamate→Glutamic Semialdehyde→Proline

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Why α-Ketoglutarate is the Correct Answer

Among the given options:

• Oxaloacetate – Precursor for Aspartate and Asparagine.
• Ribose-5-Phosphate – Precursor for nucleotides.
• Pyruvate – Precursor for Alanine, Valine, and Leucine.
• ✅ α-Ketoglutarate – Precursor for Glutamate, Glutamine, and Proline.

Therefore, α-Ketoglutarate is the correct metabolic precursor for both Proline and Glutamine.

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✅ Correct Answer:

Option 4: α-Ketoglutarate

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Importance of α-Ketoglutarate in Metabolic Pathways

• α-Ketoglutarate is a key molecule in the citric acid cycle.
• It plays a critical role in nitrogen metabolism.
• The transamination reaction involving α-Ketoglutarate is essential for amino acid biosynthesis.