Intermediary Metabolism and Regulatory Metabolism

Intermediary metabolism

Refers to the sum of all chemical transformations that occur in a cell or organism through a series of enzyme-catalyzed reactions that constitute metabolic pathways. These pathways consist of linked reactions, each catalyzed by a specific enzyme, often aided by co-enzymes and cofactors.

Key Concepts:

- Precursor: The initial substance in a metabolic pathway.

- Intermediates: Compounds formed during the metabolic process.

- Products: Final compounds produced by metabolic pathways.

- Metabolite: Any substance involved in metabolism, including precursors, intermediates, and products.

Overview of Metabolic Pathways

Intermediary metabolism encompasses the combined activities of all metabolic pathways that interconvert precursors, metabolites, and products. Metabolism has two fundamental processes:

1. Catabolism: The set of biochemical reactions that break down larger, complex molecules into simpler ones, releasing energy.

2. Anabolism: The set of biochemical reactions that build larger, more complex molecules from smaller ones, consuming energy.

Various Metabolic Pathways:

1. Glycolysis:

- Glycolysis is the process of breaking down glucose into pyruvate or lactate, generating 2 ATP molecules.

- Pyruvate is then converted to Acetyl CoA.

2. Citric Acid Cycle (TCA Cycle):

- Acetyl CoA, a key metabolite produced from different fuel sources like carbohydrates, lipids, and amino acids, enters the TCA cycle.

- Acetyl CoA is oxidized to CO₂, and most of the energy is captured in the form of NADH and FADH₂.

3. Hexose Monophosphate Shunt:

- This pathway primarily generates NADPH and ribose.

- NADPH is used for the biosynthesis of several compounds, including fatty acids.

- Ribose is an essential component of nucleotides and nucleic acids.

4. Fatty Acid Oxidation:

- Fatty acids undergo sequential degradation, releasing Acetyl CoA.

- The energy is captured in the form of NADH and FADH₂.

5. Amino Acid Degradation:

- When amino acids are consumed in excess of what is required for protein synthesis, they are degraded to meet the body's energy demands.

- Glucogenic amino acids serve as precursors for glucose synthesis.

- Ketogenic amino acids are precursors for Acetyl CoA.

6. Oxidative Phosphorylation:

- NADH and FADH₂, produced in different metabolic pathways, are oxidized in the electron transport chain, producing ATP.

7. Gluconeogenesis:

- The synthesis of glucose from non-carbohydrate sources, such as pyruvate, glycerol, and amino acids.

8. Glycogen Metabolism:

- Glycogen is the storage form of glucose, primarily found in the liver and muscles.

- It is synthesized and degraded by independent pathways, serving as a fuel reserve to meet the body's energy needs.

Regulatory Mechanisms

Metabolic pathways are regulated by mechanisms that affect the activity of existing enzymes through allosteric modulation and covalent modification. These changes are often initiated by hormones, which regulate metabolism by promoting or inhibiting the synthesis of enzymes through changes in gene expression.

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