Recording-2025-02-25T18:15:55.321Z

Introduction to Metabolism

  • Metabolism: Totality of an organism's chemical reactions; an emergent property of life arising from orderly interactions between molecules.

  • Energy Flow: All organisms utilize energy withdrawn from organic compounds to perform work, which can include transport mechanisms like endocytosis and exocytosis, as well as bioluminescence in some organisms.

Major Metabolic Pathways

  • Cellular Respiration: Metabolic pathway present in animal and plant cells.

  • Photosynthesis: Exclusive pathway for plant cells and photosynthetic microorganisms.

Bioluminescence Example

  • Puerto Rican Algae: Microorganisms that absorb light energy and release it as light during metabolic pathways when stimulated by mechanical disturbances, such as water movement.

  • Mechanism: Waves disturb the algae, creating a chemical reaction that causes glowing, a beautiful natural phenomenon.

Understanding Metabolic Pathways

  • Definition: A metabolic pathway is not just a single reaction but several sequential chemical reactions starting from a substrate to a final product.

  • Process Explanation:

    • Start with molecule A, which is transformed into product B (first reaction).

    • B becomes substrate for the next reaction, producing C.

    • C becomes substrate for another reaction, culminating in final product D.

Types of Metabolic Pathways

  1. Catabolic Pathways

    • Function: Breakdown of larger, complex molecules into simpler ones.

    • Example: Glucose breaking down into carbon dioxide and water during cellular respiration, releasing energy (exergonic process).

  2. Anabolic Pathways

    • Function: Build larger, complex molecules from smaller ones, requiring energy (endergonic process).

    • Example: Synthesizing lipids or other complex biological molecules.

Bioenergetics

  • Defined as the study of energy flow through living organisms.

  • Involves both catabolic and anabolic pathways to maintain metabolic function.

Energy Fundamentals

  • Definition of Energy: Capacity to cause change;

    • Potential Energy: Stored energy due to position.

    • Kinetic Energy: Energy of motion.

  • Energy Transformation: In cells, potential energy can be transformed into chemical or kinetic energy.

Thermodynamics Laws

  1. First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.

  2. Second Law of Thermodynamics: In isolated systems, energy transformation increases entropy (chaos) in a closed system.

Factors Affecting Energy in Systems

  • Temperature: Affects molecular movement and reaction rates.

  • Entropy: The level of disorder; higher entropy means less energy available.

  • Enthalpy: Total energy of a system.

Free Energy and Gibbs Energy

  • Free Energy Variation (ΔG): The energy available for work during a reaction; calculated as final energy minus initial energy.

  • Significance of ΔG:

    • Negative ΔG indicates a spontaneous process; energy is released.

    • Positive ΔG indicates a non-spontaneous process; energy is absorbed.

Enzyme Function in Metabolic Pathways

  • Enzymes: Catalytic proteins that speed up chemical reactions by lowering activation energy without altering ΔG.

  • Mechanism: Substrate binds to the enzyme's active site forming an enzyme-substrate complex, facilitating transition to product.

  • Factors Influencing Enzyme Activity:

    • Concentration of substrates.

    • Temperature and pH (optimal conditions for each enzyme).

    • Presence of cofactors (vitamins, ions) that support enzymatic activity.

Enzyme Inhibition

  1. Competitive Inhibition: Inhibitor competes with substrate for the active site; increasing substrate concentration can overcome inhibition.

  2. Noncompetitive Inhibition: Inhibitor binds to a different site and changes enzyme shape, preventing substrate binding; increasing substrate does not help.

Feedback Mechanisms in Metabolism

  • Negative Feedback: The end product of a metabolic pathway inhibits an early step, preventing overproduction and maintaining homeostasis.

    • Example: High ATP levels inhibit the production of the hormone thyroxine, regulating metabolism.

ATP as Energy Currency

  • Adenosine Triphosphate (ATP): Key energy carrier in cells; hydrolysis of ATP releases energy that drives endergonic reactions.

  • Synthesis of ATP: Occurs through cellular respiration, replenishing ATP supply needed for various cellular activities.

Conclusion

  • Dynamic Nature of Cells: Cells exist as open systems with constant energy and material flow, never reaching equilibrium, allowing ongoing metabolic processes to sustain life.