What are the inputs of glycolysis?

• A. 2 ATP, NAD+, glucose
• B. 2 ATP, glucose, 2 NADH
• C. 2 ATP, glucose, 2 NAD+
• D. Glucose only

Answer: (C)

The inputs to glycolysis are glucose, two ATP molecules, and two NAD+. Glucose is the starting substrate, and two ATP are consumed in the early investment phase to phosphorylate and partially activate the sugar, which drives the pathway forward. Two molecules of NAD+ are required as electron acceptors and are reduced to NADH in the oxidation steps that follow. This means glycolysis uses NAD+ and produces NADH, so NAD+ must be present as an input, not NADH. That’s why the option listing two ATP, glucose, and two NAD+ is the correct set. The other options either place NADH (which is produced, not consumed), omit the ATP investment, or omit NAD+ altogether.