Energy and Chemical Reactions

Energy and Chemical Reactions

  • Key Concepts:

    • The direction and rate of chemical reactions in living cells are governed by energy changes.

    • Energy-intermediate molecules (e.g., ATP) drive chemical reactions in a desired direction.

    • Definition of Energy: The ability to perform work or cause change.

Forms of Energy

  • Kinetic Energy: Energy associated with movement (e.g., a moving baseball bat).

  • Potential Energy: Stored energy based on position or state (e.g., an arrow drawn in a bow).

    • Chemical Potential Energy: Potential energy stored in chemical bonds; released during bond breaking.

Table of Energy Types in Biology:

Energy Type

Description

Biological Example

Light

Electromagnetic radiation energy packaged in photons.

Photosynthesis in chloroplasts.

Heat

Transfer of kinetic energy from warmer to cooler areas.

Thermoregulation in humans.

Mechanical

Energy of movement or position.

Muscle contractions during walking.

Chemical

Energy stored in molecular bonds.

Energy in ATP and glucose.

Electrical/Ion Gradient

Energy due to charge movement.

Electrochemical gradients during cellular respiration.

Thermodynamics in Biology

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

  • Second Law of Thermodynamics: Energy transformations increase system entropy (disorder).

    • Entropy measures randomness (more disorder = higher entropy).

Free Energy and Reactions

  • Free Energy (G): Usable energy available to do work.

    • Gibbs Free Energy Equation: H=G+TS

    • H: Enthalpy (total energy)

    • S: Entropy

    • T: Absolute temperature (K)

    • G: Free energy (useable)

    • TS: (unusable energy)

  • Exergonic Reactions:

    • Energy-releasing; negative free energy change (ΔG < 0)(Less than); spontaneous reactions favor product formation.

  • Endergonic Reactions:

    • Energy-requiring; positive free energy change (ΔG > 0) (greater than); non-spontaneous reactions.

Importance of ATP in Energy Metabolism

  • ATP Hydrolysis:

    • ATP → ADP + P (Pi) + energy; ΔG = -7.3 kcal/mol.

    • Cells use energy from ATP hydrolysis to drive endergonic reactions (e.g., phosphorylation of glucose).

Enzymes and Catalysis

  • Enzymes: Biological catalysts that speed up reactions without being consumed.

  • Activation Energy (Eₐ): Energy required to initiate reaction, lowered by enzymes.

    • Enzymes lower activation energy via:

    • Straining chemical bonds in reactants.

    • Proper orientation of substrate molecules.

Enzyme Specificity and Regulation

  • Active Site: Region in enzyme where reaction occurs, specifically binds substrates.

  • Induced Fit Model: Enzyme changes shape to improve fit after substrate binds, enhancing catalysis.

Velocity of Reactions and Inhibitors

  • Reaction Velocity: Amount of product formed per time unit; influenced by substrate concentration.

  • Michaelis Constant (Kₘ): Measures substrate concentration at which reaction velocity is half max.

    • A low Kₘ value implies high enzyme affinity for substrate.

  • Inhibitors:

    • Competitive Inhibitors: Compete with substrate for active site.

    • Noncompetitive Inhibitors: Bind elsewhere on the enzyme, reducing its activity without blocking the active site.

Metabolic Pathways

  • Catabolic Reactions: Breakdown of larger molecules into smaller, releasing energy (e.g., glycolysis and citric acid cycle).

  • Anabolic Reactions: Synthesis of larger molecules from smaller, requiring energy (e.g., biosynthesis).

  • Control of Metabolic Pathways: Regulated at genetic, cellular, and biochemical levels (feedback inhibition, substrate availability).