tricarboxylic acid metabolic process

Definition

Target type: biologicalprocess

The chemical reactions and pathways involving dicarboxylic acids, any organic acid containing three carboxyl (COOH) groups or anions (COO-). [GOC:mah]

The tricarboxylic acid (TCA) cycle, also known as the Krebs cycle or citric acid cycle, is a series of chemical reactions that are central to cellular respiration and energy production in living organisms. It occurs in the mitochondria of eukaryotic cells and in the cytoplasm of prokaryotic cells. The cycle starts with the condensation of acetyl-CoA (derived from carbohydrates, fats, and proteins) with oxaloacetate to form citrate. Through a series of eight enzymatic reactions, citrate is then converted back to oxaloacetate, generating ATP, reduced electron carriers (NADH and FADH2), and carbon dioxide as byproducts. Here's a detailed breakdown:

1. **Condensation:** Acetyl-CoA, a two-carbon unit, combines with oxaloacetate (a four-carbon molecule) to form citrate (a six-carbon molecule). This reaction is catalyzed by citrate synthase.

2. **Isomerization:** Citrate is isomerized to isocitrate by the enzyme aconitase. This involves the removal of water followed by the addition of water to form a different isomer.

3. **Oxidative decarboxylation:** Isocitrate is oxidized to α-ketoglutarate (a five-carbon molecule) by the enzyme isocitrate dehydrogenase. This step produces NADH and releases carbon dioxide.

4. **Oxidative decarboxylation II:** α-ketoglutarate is oxidized to succinyl-CoA (a four-carbon molecule) by the enzyme α-ketoglutarate dehydrogenase complex. This step also generates NADH and releases carbon dioxide.

5. **Substrate-level phosphorylation:** Succinyl-CoA is converted to succinate by the enzyme succinyl-CoA synthetase. This reaction involves the transfer of a phosphate group from succinyl-CoA to GDP, generating GTP (guanosine triphosphate). GTP can then be used to generate ATP.

6. **Oxidation:** Succinate is oxidized to fumarate by the enzyme succinate dehydrogenase. This step produces FADH2.

7. **Hydration:** Fumarate is hydrated to malate by the enzyme fumarase.

8. **Oxidation II:** Malate is oxidized to oxaloacetate by the enzyme malate dehydrogenase. This step generates NADH and completes the cycle, regenerating oxaloacetate for the next round of reactions.

**Key Functions of the TCA Cycle:**

* **Energy production:** The TCA cycle is a major source of ATP, the primary energy currency of cells.
* **Anabolic precursor production:** Intermediates of the TCA cycle serve as precursors for the biosynthesis of various molecules, including amino acids, heme, and glucose.
* **Regulation of cellular metabolism:** The TCA cycle is tightly regulated by feedback mechanisms that ensure proper energy production and the supply of metabolic precursors.

**Overall, the TCA cycle is a crucial metabolic pathway that links the breakdown of carbohydrates, fats, and proteins to the production of energy and essential cellular building blocks.**'
"

Proteins (2)

Compounds (5)