Glycolysis products – identify what is NOT produced Which of the following molecules is not generated at any step of the glycolytic pathway (from glucose to pyruvate)?

Introduction / Context:
Glycolysis is a ten-step pathway converting glucose to pyruvate, capturing energy via substrate-level phosphorylation and reducing power in the form of NADH. Knowing exactly which cofactors and nucleotides are consumed versus produced prevents common exam errors.

Given Data / Assumptions:

• NAD⁺ is required as an oxidizing agent at the glyceraldehyde-3-phosphate dehydrogenase step.
• NADH is produced from the reduction of NAD⁺.
• ATP is both consumed (investment phase) and produced (payoff phase).
• ADP is formed when ATP is consumed and serves as a substrate when ATP is produced.

Concept / Approach:
During glycolysis, NAD⁺ is consumed (reduced) to NADH and must be regenerated elsewhere (e.g., by the ETC in aerobic cells or by fermentation pathways). Thus, NAD⁺ is not a product; it is a reactant. By contrast, NADH, ATP, ADP, and pyruvate all appear as outputs at various steps (net: 2 ATP, 2 NADH, 2 pyruvate per glucose).

Step-by-Step Solution:
Track cofactors: NAD⁺ + electrons → NADH (produced), meaning NAD⁺ is consumed.Track nucleotides: ATP consumed early → ADP appears; later ADP → ATP produced.End product: pyruvate is formed.Therefore, the molecule not produced in glycolysis is NAD⁺.

Verification / Alternative check:
Stoichiometry per glucose: glucose + 2 ADP + 2 Pi + 2 NAD⁺ → 2 pyruvate + 2 ATP + 2 NADH + 2 H⁺ + 2 H₂O, confirming NAD⁺ is a substrate, not a product.

Why Other Options Are Wrong:

• NADH: produced at the oxidation of glyceraldehyde-3-phosphate.
• ADP: produced when ATP is consumed in early steps.
• ATP: generated by substrate-level phosphorylation at two later steps.
• Pyruvate: the final carbon product of glycolysis.

Common Pitfalls:
Confusing cofactor regeneration outside glycolysis (e.g., ETC or fermentation) with glycolytic steps themselves.

Final Answer:
NAD⁺.