What molecules are made during the Krebs cycle and are later used in the electron transport chain?
The correct answer and explanation is :
During the Krebs cycle (also called the citric acid cycle or TCA cycle), the molecules produced that are later used in the electron transport chain (ETC) are:
- NADH (Nicotinamide Adenine Dinucleotide, Reduced Form)
- FADH₂ (Flavin Adenine Dinucleotide, Reduced Form)
These molecules are essential because they carry high-energy electrons to the electron transport chain, where they contribute to ATP production through oxidative phosphorylation.
Explanation (300 Words):
The Krebs cycle occurs in the mitochondrial matrix and is a central metabolic pathway that completes the oxidation of acetyl-CoA, derived from carbohydrates, fats, and proteins. The main function of the cycle is to generate high-energy electron carriers (NADH and FADH₂) and metabolic intermediates.
During the cycle, NAD⁺ is reduced to NADH in three key steps:
- Isocitrate to α-Ketoglutarate (via isocitrate dehydrogenase)
- α-Ketoglutarate to Succinyl-CoA (via α-ketoglutarate dehydrogenase)
- Malate to Oxaloacetate (via malate dehydrogenase)
Similarly, FAD is reduced to FADH₂ when succinate is converted to fumarate by succinate dehydrogenase, an enzyme that is uniquely embedded in the inner mitochondrial membrane and directly linked to the ETC.
Once NADH and FADH₂ are produced, they transfer their high-energy electrons to Complex I (NADH dehydrogenase) and Complex II (succinate dehydrogenase) of the ETC, respectively. This electron transfer leads to the pumping of protons into the intermembrane space, creating a proton gradient. The stored energy in this gradient is then used by ATP synthase to generate ATP via chemiosmosis.
Thus, the Krebs cycle is crucial because it provides the electron donors (NADH and FADH₂) that drive ATP production in the ETC, ultimately supplying the energy required for cellular activities.