01: Cellular Metabolism and Regulation

Introduction to Cellular Metabolism

• Metabolism: Sum of all chemical reactions within a cell.

• Anabolism: Synthesis of complex molecules from simple precursors (building processes).

• Catabolism: Breakdown of complex molecules into simpler forms, releasing energy.

Regulation in Metabolism

• Metabolic Regulation: Involves feedback mechanisms to maintain homeostasis.

• Regulatory Feedback: Process in which a portion of the output returns as input.

  • Negative Feedback: Common in physiology; inhibits earlier steps in pathways to prevent excess.

  • Positive Feedback: Activates earlier steps to enhance process completion.

Control Mechanisms in Metabolism

• Main Control Mechanisms:

• Concentration levels of substrates and enzymes.

• Compartmentalization in different cellular organelles.

• Activation and deactivation of enzymes.

• Reciprocal regulation of opposing pathways.

Concentration Mechanisms

• Enzymes: Levels influenced by gene expression. More enzymes can lead to increased reaction rates (Kcat).

• Substrates: Higher concentrations of substrate lead to increased product formation.

• Cofactors: Essential for enzyme activity and influence metabolic outcomes.

Compartmentalization

• Enzymatic pathways exist in distinct cellular locations to facilitate precise control. For instance:

• Nucleus: DNA/RNA synthesis.

• Mitochondria: Krebs cycle and fatty acid metabolism.

• Cytosol: Glycolysis and fatty acid synthesis.

Enzyme Activity Control

• Covalent Modifications: Attachment/detachment of phosphate groups (phosphorylation) alters enzyme function.

• Kinases: Add phosphate groups.

• Phosphatases: Remove phosphate groups.

Diet and Nutrition in Metabolism

• Energy Sources: Diet provides carbohydrates, lipids, and proteins, which are necessary for metabolic energy.

  • Carbohydrates: Provide energy value (4 kcal/g)

  • Lipids: Higher energy value (9 kcal/g)

  • Proteins: Similar energy to carbohydrates (4 kcal/g)

ATP and Coenzyme A

• ATP (Adenosine Triphosphate): Stores and transfers energy within cells.

• Hydrolysis of phosphate bonds releases large amounts of energy.

• Coenzyme A (CoA): Transfers acyl groups and plays an essential role in fatty acid metabolism.

Redox Cofactors in Metabolic Pathways

• Redox Reactions: Essential for energy production; involve electron transfer (OIL RIG method).

• Common Redox Cofactors:

  • NAD+/NADH and NADP+/NADPH: Participates in various metabolic reactions.

  • FAD/FADH2: Important in oxidation reactions.

Vitamins Essential for Metabolism

• Various vitamins act as cofactors in biochemical reactions:

• Thiamine (Vitamin B1): Cofactor in decarboxylation reactions.

• Riboflavin (Vitamin B2): Part of FAD.

• Nicotinamide (Vitamin B3): Component of NAD and NADP.

• Pantothenic Acid (Vitamin B5): Essential for CoA synthesis.

• Biotin (Vitamin B7): Cofactor in carboxylation reactions.

Summary of Metabolic Pathways

• Stages of Digestion:

• Stage I: Breakdown of large biomolecules into building blocks.

• Stage II: Conversion of building blocks to simple intermediates (acetyl groups).

• Stage III: Further breakdown to CO2, NH3 and water.

Overall, understanding these aspects of metabolism, including the roles of different components and regulatory mechanisms, is crucial for grasping cellular energy dynamics and biochemical processes.