The image below shows she reactions of the cltric acid cycle

Step 1 of 2

TCA cycle starts when the Acetyl CoA formed from the degradation of proteins, lipids, and carbohydrates is entered into the mitochondrial matrix. Then, this acetyl CoA is reacted with the oxaloacetic acid to form citric acid. This citric acid is further converted into oxaloacetic acid by a series of chemical reactions.

Explanation | Hint for next step

The eight chemical reaction steps of TCA cycle are:

1. In the first step of TCA cycle, the acetyl CoA is reacted with the oxaloacetic acid to form citrate by the enzyme citrate synthase. It is a five carbon compound having three carboxylic groups. That’s why the name of this cycle is given as tricarboxylic acid cycle.

2. In the second step, citrate is converted into isocitrate by the enzyme aconitase. It is a reversible reaction.

3. In the third step, isocitrate is converted into α ketoglutarate with the release of one NADH (reduced nicotinamide adenine dinucleotide) and CO₂ by the enzyme isocitrate dehydrogenase.

4. In the fourth step, α- ketoglutarate is further converted into succinyl CoA by the enzyme α ketoglutarate dehydrogenase with the release of one molecule of CO₂ and NADH.

5. In the fifth step, succinyl CoA formed in the fourth step is further converted into the succinate by the enzyme succinyl CoA synthetase with a release of energy in the form of GTP (guanosine triphosphate).

6. In the sixth step, the compound succinate is converted into the fumarate by the enzyme succinate dehydrogenase with the release of reduced energy in the form of FADH₂ (Flavin adenine dinucleotide).

7. In the seventh reaction, the fumarate is converted into the malate by the enzyme fumarase.

8. In the final reaction, the malate is converted into the oxaloacetate with the release of another NADH molecule by the enzyme malate dehydrogenase.

Step 2 of 2

In TCA cycle, the acetyl CoA is degraded into oxaloacetic acid with the release of energy in the form of GTP and reduced energy in the form of NADH and FADH. These reactions come under the catabolism. TCA cycle is also an anabolic pathway because intermediate compounds formed in the TCA cycle are involved in other metabolic processes like fatty acid synthesis, Cholesterol production, and amino acid synthesis. Thus, the TCA cycle is called amphibolic pathway.Explanation

Tricarboxylic acid cycle is a series of eight chemical reactions, in which each reaction is catalyzed by a specific enzyme. The conversion of isocitrate to α-ketoglutarate is catalyzed by the enzyme isocitrate dehydrogenase. This step is the rate-limiting step of TCA cycle, because this is the slowest step of TCA cycle.

Energetics of TCA cycle:

The aim of the TCA cycle is to generate a huge amount of energy in the form of ATPs. Each NADH gives 3 ATPs, whereas FADH gives 2 ATPs. The reduced energy in the form of NADH and FADH formed in TCA cycle are entering into ETC (electron transport chain) to generate ATPs. Through each TCA cycle, 3 NADH, 1 FADH, and 1GTP are produced. The overall ATPs generated by each acetyl CoA from a TCA cycle is 12 ATPs. They are as follows:

3 NADH: 9 ATPs

1 FADH: 2 ATPs

1 GTP: 1 ATP.

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