krebs cycle

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KREBS CYCLE
It refers to a complex series of chemical reactions that produce carbon dioxide and Adenosine triphosphate (ATP), a compound rich in energy. The cycle occurs by essentially linking two carbon coenzyme with carbon compounds; the created compound then goes through a series of changes that produce energy. This cycle occurs in all cells that utilize oxygen as part of their respiration process. It occurs in the matrix of the mitochondria in the presence of CO2.Pyruvic acid diffuses from cytoplasm to the matrix of the mitochondria.Pyruvic acid is oxidized and broken down into energy,CO2 and H2O as shown; CH3COCOOH + O2 CO2 + H2O + Energy

Diagram showing the Krebs Cycle

Other names of Krebs Cycle;
Citric Acid Cycle
Tricarboxylic Acid Cycle
Stages in which C02, H2O and Energy is released;
1: Glycolysis ("splitting of sugar"): This step happens in the cytoplasm. One Glucose (C6H12O6) is broken down to 2 molecules of pyruvic acid. Results in the production of 2 ATPs for every glucose 2: Transition Reaction: Pyruvic Acid is shuttled into the mitochondria, where it is converyed to a molecule called Acetyl CoA for further breakdown. 3: The Krebs Cycle, or Citric Acid Cycle: Occurs in the mitochondrial matrix, the liquid part of the mitochondria. 4: The Electron Transport Chain and Chemiosmosis ("the big ATP payoff"). Occurs in the christae of the mirochondria, the folded membranes inside the chloroplast. How many Enzymes are involved in the Krebs Cycle?

There are 8 enzymes involved in the cycle.These are;
1. Citrate
2. Isocitrate
3. Alpha-ketoglutarate
4. Succinul-CoA
5. Succinate
6. Malate
7. Fumarate
8. Oxaloacetate
How many Stages does the cycle have?

a)Formation of acetyl CoA
The raw material for citric acid cycle is acetyl CoA. It is formed from fatty acids by b-oxidation and from pyruvic CoA to form Acetyl Co A. This reaction is catalysed by a set of enzymes called pyruvic acid dehydrogenase. In this reaction, 2 hydrogen atoms and one CO2 molecule are removed. Hence this reaction is called oxidative decarboxylation. The 2 hydrogen atoms are accepted by NAD and NAD is converted into NADH. b) Formation of citric acid

The acetyl- CoA combines with oxaloacetic acid to form citric acid. It contains 6 carbon atoms. This reaction is catalysed by an enzyme called citric acid synthetase. c) Dehydration
Citric acid undergoes dehydration and forms cis-aconitic acid. This reaction is catalysed by the enzyme aconitase. d) Hydration
The aconitic acid is hydrated and it forms isocitric acid. This reaction is catalysed by the enzyme aconitase. e) Dehydrogenation I
Isocitric acid undergoes dehydrogenation in the presence of isocitric acid dehydrogenase to form oxalo succinic acid. In this reaction 2 hydrogen atoms are released. They are accepted by NAD+ to form NADH. formation of nadh in citric acid cycle

f) Decarboxylation
The oxalo succinic acid undergoes decarboxylation to form a-ketoglutaric acid. This reaction is catalysed by decarboxylase. In this reaction one CO2 is eliminated. Hence the a-ketoglutaric acid has only 5 carbon atoms. g) Oxidative decarboxylation

During oxidative decarboxylation a-ketoglutaric acid is converted into succinyl CoA. This reaction is catalysed by a-ketoglutaric acid dehydrogenase. Two hydrogen atoms are released and they are transferred to NAD. The NAD is converted into NADH. In the next step, the succinyl CoA is decarboxylated to succinic acid. This step is catalysed by succinic acid thiokinase. CoA is liberated. h) Oxidation

Succinic acid is oxidised to fumaric acid by the removal of 2 hydrogen atoms. The reaction is catalysed by succinic acid dehydrogenase. The hydrogen atoms are accepted by FAD and it forms FADH2. i) Hydration

Fumaric acid undergoes hydration to form malic acid. This reaction is catalysed by fumarase. j) Dehydrogenation
It is the final step in Krebs cycle. Oxalo acetic acid is regenerated from malic acid by a...
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