Question

Describe Krebs cycle. (Flow chart or explanation).

Answer 1

Hint: Krebs cycle is a part of aerobic respiration. Aerobic respiration is the process which occurs in the presence of Oxygen to convert food into carbon dioxide, water and energy. Kreb’s cycle is also called the Citric acid cycle or TCA (tricarboxylic acid) cycle.

Complete Answer:
- This cycle is a series of chemical reactions in all aerobic organisms to release energy.
- In the Krebs cycle Acetyl coenzyme A which is derived from the fats, proteins and carbohydrates get oxidized.
- This cycle occurs in the matrix of Mitochondria of a cell.
- Oxidative decarboxylation of pyruvate to Acetyl coenzyme A.
- This is the linkage step between the glycolysis and Kreb’s cycle.
- In this step, the end product of glycolysis i.e the pyruvate is oxidatively decarboxylated to acetyl coenzyme A and carbon dioxide with the help of enzyme pyruvate dehydrogenase.

Steps involved in Krebs cycle:
There are a total 8 steps occurred in the Krebs cycle. These all eight steps are enzyme catalysed.

Sl.No.	Steps involved in Krebs cycle	Enzyme used
1.	Condensation of acetyl coenzyme A with Oxaloacetate	Citrate synthase
2.	Isomerisation of citrate into isocitrate	Aconitase
3.	Oxidative decarboxylation of isocitrate	Isocitrate dehydrogenase
4.	Oxidative decarboxylation of alpha-ketoglutarate	Alpha-ketoglutarate dehydrogenase
5.	Conversion of succinyl-coA into succinate	Succinyl-coA synthase
6.	Dehydration of succinate to fumarate	Succinate dehydrogenase
7.	Hydration of fumarate to malate	Fumarate hydratase
8.	Dehydration of malate to oxaloacetate	Malate dehydrogenase

Products of Krebs cycle:
- Since Kreb’s cycle is a cyclic process, the Oxaloacetate formed at the end of this cycle combines with the acetyl coenzyme A in the next cycle.
- At each turn of Krebs cycle, following energy molecules are produced as-
3 NADH, 1 FADH2, 1 GTP (OR ATP) and 2 Carbon Dioxide molecules

Note: Remember to keep in mind that the Krebs cycle takes place in the Mitochondria of a cell and its purpose is to complete the oxidation of Glucose and producing energy rich molecules that later produce ATP in the Electron transport chain.