The document summarizes the conversion of pyruvic acid to acetyl-CoA and the reactions of the citric acid (TCA) cycle. It describes the 8 reactions of the cycle, including the formation of citrate by citrate synthase and the oxidation of malate to oxaloacetate by NAD+-dependent malate dehydrogenase. It also provides calculations of the ATP generated at different stages of glycolysis, the conversion of pyruvic acid to acetyl-CoA, and through the various electron carriers in the TCA cycle, giving a net total of 36-38 ATP.

1. Conversion of pyruvic acid to acetyl-CoA

2. Conversion of pyruvic acid into acetyl-CoA

3. Tricarboxylic Acid
cycle, Citric Acid
cycle, Krebs Cycle

5. Reactions of Citric Acid Cycle
1.Citrate synthase: Formation of Citric acid

6. 2. Aconitase: This enzyme catalyses the isomerization reaction by
removing and then adding back the water ( H and OH ) to cis-aconitate
in at different positions. Isocitrate is consumed rapidly by the next
step thus deriving the reaction in forward direction.

7. 3. Isocitrate dehydrogenase: There are two isoforms of this enzyme,
one uses NAD+
and other uses NADP+

8. 4. α-Ketoglutarate dehydrogenase:

9. 5. Succinyl CoA syntheatse: Sccinyl CoA, like Acetyl CoA has a
thioester bond. In this reaction, the hydrolysis of the thioester bond
leads to the formation of phosphoester bond with inorganic
phosphate. This phosphate is transferred to Histidine residue of the
enzyme and this high energy, unstable phosphate is finally
transferred to GDP resulting in the generation of GTP.

10. 6. Succinate Dehydrogenase: Oxidation of succinate to fumarate. It is
an FAD dependent enzyme.

11. 7. Fumarase: Hydration of Fumarate to malate: It is a highly
stereospecific enzyme.

12. 8. L-Malate dehydrogenase: Oxidation of malate to oxaloacetate: It is an
NAD+
dependent enzyme.

13. Energetics
ATPs glycolysis 08
Pyruvic acid to acetyl CoA (NADH)2X3 = 06
TCA cycle (3 NADH) 9X2 = 18
TCA cycle (1FADH) 2X2= 04
TCA cycle (1GTP) 2X1= 02
Net ATPs = 38

15. Energetics
ATPs glycolysis 06
Pyruvic acid to acetyl CoA (NADH)2X3 = 06
TCA cycle (3 NADH) 9X2 = 18
TCA cycle (1FADH) 2X2= 04
TCA cycle (1GTP) 2X1= 02
Net ATPs = 36