Question:medium
Which of the following steps is specific for gluconeogenesis?
Which of the following steps is specific for gluconeogenesis?
Show Hint
Look for the PEP carboxykinase bypass reaction.
Updated On: Jun 24, 2026
- Pyruvate to acetyl CoA
- Oxaloacetate to citrate
- Oxaloacetate to phosphoenolpyruvate (PEP)
- Malate to oxaloacetate
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: To find a gluconeogenesis-specific step, look for a reaction that exists only in glucose synthesis and nowhere else among the choices.
Step 2: The PEP carboxykinase reaction turns oxaloacetate into phosphoenolpyruvate, releasing carbon dioxide and using GTP. This is one of the four key bypass enzymes that distinguish gluconeogenesis from glycolysis.
Step 3: The other options are not exclusive. Pyruvate to acetyl CoA feeds the TCA cycle, while oxaloacetate to citrate and malate to oxaloacetate are ordinary TCA cycle reactions that operate independently of glucose synthesis.
Step 4: Hence the reaction unique to gluconeogenesis is oxaloacetate to PEP.
\[\boxed{\text{Oxaloacetate to PEP}}\]
Step 2: The PEP carboxykinase reaction turns oxaloacetate into phosphoenolpyruvate, releasing carbon dioxide and using GTP. This is one of the four key bypass enzymes that distinguish gluconeogenesis from glycolysis.
Step 3: The other options are not exclusive. Pyruvate to acetyl CoA feeds the TCA cycle, while oxaloacetate to citrate and malate to oxaloacetate are ordinary TCA cycle reactions that operate independently of glucose synthesis.
Step 4: Hence the reaction unique to gluconeogenesis is oxaloacetate to PEP.
\[\boxed{\text{Oxaloacetate to PEP}}\]
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