KREB CYCLE / CITRIC ACID CYCLE / TCA CYCLE

KREB CYCLE/ CITRIC ACID CYCLE / TRICARBOXYLIC (TCA) CYCLE

Important points of Kreb cycle

1) It was discovered by Sir Hans Adolf Krebs in the year 1948

2) Kreb cycle is also known as Citric acid cycle or Tricarboxylic acid (TCA) cycle

3) All reactions of Kreb cycle takes place in matrix of mitochondria, because all the enzymes are found in the matrix itself except Succinic dehydrogenase which is present in the membrane of mitochondria.

4) It is basically a catabolic reaction as, it oxidises acetyl Co-A into CO2 and H2O but, it acts as an amphibolic pathway because it serves in both catabolic and anabolic processes.

5) One molecule of pyruvic acid after entering into mitochondria undergoes 03 decarboxylation, 05 oxidation and yields 15 ATP molecules.

Formation of acetyl Co-A

1) The pyruvic acid generated in glycolysis enters into mitochondria, undergoes oxidative decarboxylation and forms acetyl Co-A

2) This reaction is catalyzed by enzyme pyruvate dehydrogenase complex having decarboxylase, lipoic acid, TPP (Thiamine pyrophosphate), transacetylase and Mg2+.

    Pyruvic acid + Co-A + NAD+        Converts into         Acetyl Co-A + NADH+H+ + CO2

3) This Acetyl Co-A acts as connecting link between glycolysis, Kreb Cycle and oxidation of fats

4) This is an irreversible reaction and produces 02 molecules of NADH+H+ , 02 molecules of CO2 , and 02 molecules of Acetyl Co-A.

5) The NADH+H+ enters into Electron transport chain and form ATP.

Total ATP gain during Kreb Cycle

In citric acid cycle per turn 01 molecule of Acetyl Co-A generates 12 ATP molecules, as we know that there were 02 molecules of Pyruvic acid during glycolysis process, thus a total of 24 ATP’s are generated.

1) Iso citrate dehydrogenase 2NADH                                      06 ATP

2) α- Ketoglutarate dehydrogenase 2NADH                          06 ATP

3) Succinate thiokinase 02 ATP                                                02 ATP

4) Succinate dehydrogenase 2FADH+H+                                04 ATP

5) Malate Dehydrogenase 2NADH                                          06 ATP

Total ATP during Kreb Cycle                                                  24 ATP

Total ATP gain during breakdown of 01 Glucose Molecule

Total energy received during breakdown of glucose molecule under aerobic conditions.

1) Glycolysis                                                                                                                      08 ATP

(Conversion of 01 molecule of glucose into 02 molecules of pyruvic acid)

2) Formation of Acetyl Co-A                                                                                          06 ATP

(Pyruvate dehydrogenase 02 NADH) 

3) Citric Acid Cycle                                                                                                          24 ATP

(Oxidation of 02 molecules of Acetyl Co-A) 

Total ATP’s per molecule of glucose                                                                               38 ATP

Youtube Video link :- Best way to learn Kreb Cycle