please describe me kreb's cycle

 

Krebs cycle is a set of biochemical reactions which are a part of aerobic respiration and utilize acetate generated from carbohydrates, fats and proteins for generation of energy. It also generates NADH in the process.

Krebs cycle takes place in the mitochondrial matrix and involves complete oxidation of pyruvate generated through glycolysis  by stepwise removal of all hydrogen atoms, which leaves three molecules of CO _2. The cycle can be explained as 

Formation of Acetyl Coenzyme A

• The product of glycolysis, i.e., pyruvate, on entering the mitochondrial matrix, undergoes Oxidative Decarboxylation, thereby producing acetyl CoA which enters Krebs cycle. 
  

Krebs cycle (Tricarboxylic acid cycle; TCA)

• Acetyl group condenses with oxaloacetic acid and water to yield citric acid (catalysed by the enzyme citrate synthase)
• Citrate isomerises into isocitrate
• Two successive decarboxylation steps follow, leading to the formation of α ketoglutaric acid, followed by succinyl CoA
• This is followed by the conversion of succinyl CoA into succinic acid (substrate level phosphorylation). In a coupled reaction, GTP is converted into GDP, simultaneously synthesising ATP from ADP.
• Conversion of one molecule of pyruvate into acetyl CoA yields 1 molecule of CO ₂ and 1 NADH.
• One Krebs cycle yields 2 CO ₂ + 3 NADH + 1 FADH ₂ + 1 ATP
• Overall equation: 
  

• For continued oxidation of acetyl CoA in TCA 2 things are required:

  • Continued replenishment of oxaloacetic acid
  • Regeneration of NAD ⁺ and FAD ⁺ from NADH and FADH ₂ respectively.