GS

Chapter_6_Metabolism

6.1 Energy and Metabolism

Key Concepts

  • Bioenergetics: Study of energy flow in living systems.

  • Metabolism: All chemical reactions within a cell or organism.

  • Metabolic Pathways: Series of reactions transforming substrates into final products (e.g., photosynthesis and cellular respiration).

Types of Reactions

  • Anabolic Pathways: Require energy to synthesize larger molecules.

  • Catabolic Pathways: Release energy by breaking down larger molecules.

Evolution of Metabolic Pathways

  • Shared pathways among life forms support the theory of evolution from common ancestors.

6.2 Potential, Kinetic, Free, and Activation Energy

Definitions

  • Energy: Ability to do work; two types:

    • Kinetic Energy: Energy of motion.

    • Potential Energy: Stored energy (e.g., in chemical bonds).

  • Gibbs Free Energy (G): Usable energy in a system; changes during reactions denoted as ΔG.

    • Exergonic Reactions: Release energy (ΔG is negative).

    • Endergonic Reactions: Require energy input (ΔG is positive).

Activation Energy

  • Required to initiate a chemical reaction by reaching a transition state. Lower in catalyzed reactions.

6.3 The Laws of Thermodynamics

Key Laws

  • First Law: Energy cannot be created or destroyed, only transformed.

  • Second Law: Energy transfer is inefficient; results in increased entropy (disorder).

6.4 ATP: Adenosine Triphosphate

ATP Structure

  • Composed of adenosine and three high-energy phosphate groups.

Function

  • ATP serves as the primary energy currency in cells.

  • ATP hydrolysis to ADP releases energy, driving endergonic reactions.

6.5 Enzymes

Role in Metabolism

  • Enzymes: Protein catalysts that lower activation energy, speeding up reactions.

  • Specific to particular reactions due to their unique 3D shapes and active sites.

Enzyme Mechanisms

  • Induced Fit Model: Enzyme changes shape to optimize binding and catalysis.

Regulation of Enzymes

  • Factors affecting enzyme activity: temperature, pH, coenzymes, and inhibitors (competitive vs. noncompetitive).

  • Feedback Inhibition: End product of a pathway inhibits an upstream enzyme, regulating metabolic pathways.