What is the primary role of ${\mathrm{NADH}}_{}$ and ${\mathrm{FADH}}_2$ in cellular metabolism?

• A. They act as electron carriers in the electron transport chain.
• B. They are involved in the synthesis of fatty acids.
• C. They function as coenzymes in the citric acid cycle.
• D. They are used as substrates in glycolysis.

Answer: (A)

Verified step by step guidance

1. Understand the context of cellular metabolism, which involves processes like glycolysis, the citric acid cycle, and oxidative phosphorylation.
2. Recognize that NADH and FADH2 are crucial molecules in cellular respiration, primarily involved in the electron transport chain.
3. Recall that during the citric acid cycle, NAD+ and FAD are reduced to NADH and FADH2, respectively, capturing high-energy electrons.
4. Identify that the primary role of NADH and FADH2 is to transport these high-energy electrons to the electron transport chain located in the inner mitochondrial membrane.
5. In the electron transport chain, NADH and FADH2 donate electrons, which are used to create a proton gradient that ultimately drives the synthesis of ATP, the energy currency of the cell.