This topic will cover the basic concepts of metabolism, including an overview of catabolism and anabolism, energy transfer in biological systems, and the role of enzymes in metabolism.
Introduction to Metabolism
Key concepts, terminology, and pathways for a foundational understanding
| Aspect | Description |
|---|---|
| Definition | The sum of all chemical reactions that occur in living cells to maintain life. |
| Purpose | - Obtain energy from nutrients - Synthesize macromolecules (proteins, lipids, nucleic acids, carbohydrates) - Eliminate waste products |
| Two Major Categories | Catabolism – breakdown of complex molecules → release energy. Anabolism – synthesis of complex molecules → consume energy. |
| Energy Currency | Adenosine triphosphate (ATP) is the primary energy‑transfer molecule. |
| Principle | Explanation |
|---|---|
| Enzyme Catalysis | Metabolic reactions are accelerated by enzymes (biological catalysts). Each enzyme is specific for a substrate and a reaction. |
| Thermodynamics | • ΔG°′ (standard free‑energy change) predicts spontaneity. • Coupled reactions link an unfavorable process (positive ΔG) to a favorable one (negative ΔG), usually via ATP hydrolysis. |
| Regulation | • Allosteric control – effectors bind away from the active site to modulate activity. • Covalent modification – phosphorylation, acetylation, etc. • Gene expression – long‑term control of enzyme levels. |
| Compartmentalization | Eukaryotic cells separate pathways into organelles (e.g., glycolysis in cytosol, β‑oxidation in mitochondria). |
| Pathway | Location | Primary Function | Key Products |
|---|---|---|---|
| Glycolysis | Cytosol | Breaks glucose (6‑C) → pyruvate (3‑C) | 2 ATP (net), 2 NADH, pyruvate |
| Gluconeogenesis | Cytosol & mitochondria | Synthesizes glucose from non‑carbohydrate precursors | Glucose |
| Citric Acid Cycle (TCA/Krebs) | Mitochondrial matrix | Oxidizes acetyl‑CoA → CO₂, captures high‑energy electrons | 3 NADH, 1 FADH₂, 1 GTP per acetyl‑CoA |
| Oxidative Phosphorylation (ETC & ATP synthase) | Inner mitochondrial membrane | Uses electrons from NADH/FADH₂ to generate ATP | ~30‑34 ATP per glucose |
| β‑Oxidation | Mitochondrial matrix (also peroxisomes) | Fatty‑acid breakdown → acetyl‑CoA | Acetyl‑CoA, NADH, FADH₂ |
| Pentose Phosphate Pathway (PPP) | Cytosol | Produces NADPH & ribose‑5‑phosphate | NADPH, ribose‑5‑P |
| Amino‑acid catabolism | Cytosol & mitochondria | Deaminates amino acids → keto‑acids for TCA entry | α‑keto acids, NH₃ (urea cycle) |
| Urea Cycle | Liver mitochondria & cytosol | Converts toxic ammonia → urea for excretion | Urea, fumarate |
| Step | ATP (or equivalent) |
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