Q.We commonly call ATP as the energy currency of the cell. Can you think of some other energy carriers present in a cell? Name any two.

Besides ATP, the respiratory pathway generates other molecules that carry captured energy from one part of the pathway to another.

• NADH + H+ carries reducing power (and the energy associated with it) from glycolysis and the citric acid cycle to the electron transport system.
• FADH2 similarly carries reducing power generated in the citric acid cycle to the electron transport system. …

ATP is the most familiar energy currency because its energy can be spent almost anywhere in the cell, but it is not the only molecule involved in carrying energy generated during respiration. Several other carriers move captured energy from the steps where it is released to the steps where it is finally converted into ATP.

• NADH + H+: Formed when NAD+ accepts a pair of hydrogen atoms (with their electrons) — for instance during the PGAL to BPGA step of glycolysis, the pyruvate-to-acetyl-CoA link reaction, and three separate steps of the citric acid cycle. NADH carries this reducing power to the electron transport system, where its oxidation yields three ATP molecules per NADH.
• FADH2: Formed similarly when FAD+ accepts hydrogen, at one specific step of the citric acid cycle. Its oxidation at the electron transport system yields two ATP molecules per FADH2. …

Method 1

1. Recall ATP is the main spendable energy currency, but not the only energy-carrying molecule.
2. Identify NADH + H+, formed in glycolysis (PGAL→BPGA step) and at three points of the citric acid cycle.
3. Identify FADH2, formed at one step of the citric acid cycle. …