Question

How many CO₂ molecules are released in TCA cycle?

Answer 1

TCA cycle:

1. TCA cycle stands for the tricarboxylic acid cycle.
2. It is also known as Kreb's cycle or citric acid cycle.
3. It is one of the important components of aerobic respiration.
4. The acetyl CoA which is obtained from proteins, fats, and carbohydrates undergo oxidation to release stored energy in the form of ATP.

Steps involved in the TCA cycle:

1. Formation of citrate (6 carbon molecule) when acetyl CoA (2 carbon molecule) combines with oxaloacetate (4 carbon molecule).
2. Conversion of citrate to isocitrate, which is an isomer of citrate.
3. Oxidization of isocitrate to form alpha-ketoglutarate (5 carbon molecules), releasing one carbon dioxide molecule and forming one NADH molecule.
4. Oxidization of alpha-ketoglutarate to form a 4 carbon molecule which further combines with coenzyme to form succinyl CoA. As a result, one molecule each of CO₂ and NADH are released alongside.
5. Conversion of succinyl CoA to succinate (4 carbon molecules) releases one GTP molecule.
6. Conversion of succinate to fumarate, releasing one FADH₂ molecule.
7. Conversion of fumarate to malate (4 carbon molecule).
8. Conversion of malate to oxaloacetate releasing another molecule of NADH.

Release of carbon dioxide in the TCA cycle:

1. Two TCA cycles are required for one molecule of glucose.
2. Decarboxylation takes place twice in the TCA cycle forming two carbon dioxide molecules.
3. Since two cycles are required thus, 2 CO₂ molecules are released per cycle and in total 4 carbon dioxide molecules are released for one molecule of glucose in the TCA cycle.

Figure showing Kreb's cycle: