Biochem 1.13

Key Terms and Concepts

  • Delta H (ΔH): Change in enthalpy; related to heat transfer in a reaction.

  • Delta G (ΔG): Change in Gibbs free energy; indicates the spontaneity of a reaction.

  • Delta S (ΔS): Change in entropy; measures disorder within a system.

Spontaneity of Reactions

  • To make a reaction spontaneous (go forward):

    • ΔH must be negative (exothermic: heat released).

    • ΔS must be positive (increased disorder).

    • Consequently, ΔG will be negative (reaction proceeds forward and releases free energy).

Equilibrium Concepts

  • Equilibrium (K.E.Q): The state where reactants and products exist at constant concentrations (not necessarily equal).

    • Forward and backward reactions occur at the same rate.

    • Equilibrium is described with equilibrium constants (K).

  • Equilibrium Constant Expression:

    • K = [products]^[stoichiometric coefficients] / [reactants]^[stoichiometric coefficients].

    • Involves calculating reaction quotient (Q) and comparing it with K to predict reaction direction.

Response to Changes in Concentrations (Le Chatelier's Principle)

  • If Q > K: Reaction shifts to the left (increased reactants).

  • If Q = K: Equilibrium; no net change in concentrations.

  • If Q < K: Reaction shifts to the right (increased products).

Relationship Between ΔG and Equilibrium Constant

  • If K > 1: ΔG is negative; reaction favors the formation of products (exergonic).

  • If K < 1: ΔG is positive; reaction favors the formation of reactants (endergonic).

  • If K = 1: ΔG is 0; the reaction is at equilibrium.

Metabolism Overview

  • Metabolism = Anabolism + Catabolism

    • Catabolism (breaking down macromolecules):

      • Exergonic reactions (release energy, ΔG negative).

      • Increases entropy (disorder).

    • Anabolism (building macromolecules):

      • Endergonic reactions (require energy input, ΔG positive).

      • Decreases entropy (creates order).

Energy Coupling in Metabolism

  • Catabolic reactions provide energy for anabolic reactions, enabling the synthesis of essential biomolecules.

  • Example: Energy from breaking down glucose can be used to synthesize ATP (energy currency of the cell).

Important Notes on Enzymes and Reactions

  • Reactions are often facilitated by enzymes, which lower activation energy, allowing the reaction to proceed more efficiently.

  • Changes in enzyme function due to mutations can disrupt metabolic pathways, potentially leading to diseases (e.g., metabolic disorders).

Overall Summary of Metabolic Processes

  • Devices input energy (food or light) to maintain order within biological systems.

  • Nitrogen exists as ammonia; carbon dioxide is generally exhaled or used for synthesis of biomolecules.

  • Energy and resources obtained through catabolic processes are then utilized in anabolic pathways to synthesize macromolecules necessary for cellular functions.