What is the role of NAD+ in cellular respiration?

• A. It provides phosphate groups
• B. It functions as an electron carrier
• C. It is a structural component of membranes
• D. It is the enzyme that catalyzes glucose breakdown

Answer: (B)

The main idea is that NAD+ acts as an electron carrier in cellular respiration. During glycolysis, pyruvate oxidation, and the citric acid cycle, NAD+ accepts electrons (and a proton) to become NADH. This captures high-energy electrons that are later passed to the electron transport chain, where their energy helps pump protons across the membrane to drive ATP synthesis. NAD+ is then regenerated from NADH as electrons flow through the chain, allowing these metabolic pathways to continue. It’s not a source of phosphate groups, not a membrane structural component, and not an enzyme that breaks down glucose. That carrier role is what makes NAD+ essential for energy production.