Module 2 Lecture

Coupled Reactions of Metabolism

  • Overview of Coupled Reactions

    • Exploration of how pathways with multiple reactions can be favorable, despite some individual reactions being unfavorable.
    • Concept of reaction coupling to drive metabolic processes.

  • Energy Sources for Heterotrophs

    • Nutrients: Carbohydrates, fats, proteins.
    • Carbohydrates and fats typically provide energy, while proteins are often set aside for building and repair.
    • nutrients are further broken down in catabolic reactions transferring energy into ATP.

  • Thermodynamics of Metabolic Reactions

    • First Law of Thermodynamics: Energy is conserved.
    • Reactions are categorized as:
    • Catabolic Reactions: Break down molecules, release energy that is captured as ATP (e.g., energy approximately -30 kJ/mol).
    • Anabolic Reactions: Use ATP to build complex molecules (monomers to polymers).
    • Thermogenesis: Some energy is lost as heat.

  • Coupling of Reactions

    • Can occur in two or more reactions where the energy of the unfavorable reaction can be coupled with that of a favorable reaction.
    • Gibbs Energy Change (ΔG):
    • ΔG < 0: Reaction is favorable (exergonic).
    • ΔG > 0: Reaction is unfavorable (endergonic).
    • Additivity of ΔG in simple coupled reactions.
    • If you have Reaction A leads to B leads to C, then ΔG adds up to determine overall favorability.

  • Example of Coupling

    • Reaction A (+B → C contributing +3 kJ/mol, which is unfavorable) is coupled with Reaction C+D → E is -10 kJ/mol.
    • Overall reaction, A + B + D → E results in -7 kJ/mol (favorable process through coupling).

  • The Role of Enzymes

    • Enzymes speed up reactions without changing equilibrium or ΔG values.

  • Detailed Thermodynamics Calculation Example

    • Phosphoenolpyruvate (PEP) breakdown example:
    • PEP → 2-Phosphoglycerate: ΔG = -1.7 kJ/mol (favorable)
    • 3-phosphoglycerate → 2-Phosphoglycerate: ΔG = +4.6 kJ/mol (unfavorable)
    • Final Gibbs energy calculation:
      • Overall ΔG of coupling PEP to 3-phosphoglycerate: -6.3 kJ/mol.

  • ATP Composition and Hydrolysis

    • ATP has two phosphoanhydride bonds, with hydrolysis liberating energy.
    • Overall process of ATP hydrolysis is exergonic despite the endergonic nature of breaking bonds due to the formation of new bonds.
    • Common misunderstandings must be clarified regarding breaking bonds consuming energy (endergonic), yet forming new bonds releases energy (exergonic).

  • Hydrolysis in Enzymatic Reactions

    • Example: Glutamine synthetase
      overall process:
    • Glutamate + ATP → Glutamyl phosphate + ADP (driven energetically).

  • Calculating ΔG Example: Glucose-6-Phosphate

    • Process to be analyzed using reported ΔG values and adjusted methods similar to PEP reactions.
    • Conversion using PFK1; understanding equilibrium requires flipping reactions.

  • Overview of Energy Charge Regulation

    • Adenylate System: Quantitative representation of available ATP in a cell, defined as energy charge.
    • High energy charge correlates to ATP abundance, low energy charge indicates nutrient use.

  • Homeostasis of Metabolism: Catabolism vs. Anabolism

    • Homeostatic points dictate nutrient usage.
    • Use of stored nutrients (glycogen/lipids) during low energy charge conditions requiring catabolic pathways; rebuilding in high energy conditions using anabolic pathways.

  • Interdependence of Pathways and Real-World Applications

    • Plant vs. heterotroph energy acquisition and implications in metabolism pathways.

Importance of Water in Biochemical Reactions

  • Hydrogen Bonding

    • Water's unique properties stem from its ability to form hydrogen bonds, ultimately giving rise to polar interactions in biochemical processes.
    • Ion-Dipole Interaction: Water molecules organize due to ionic interactiveness, explaining why substances dissolve/mix.

  • Osmosis

    • The process of water diffusion across semipermeable membranes, crucial in cellular homeostasis.

  • Acid-Base Chemistry Basics

  • Review of acid-base concepts, including the ionization of water and its role in pH.

Detailed Acid-Base Principles with Amino Acids

  • Ionization of Amino Acids

    • Focus on amino acids, with their functional groups influencing acid-base properties.

  • Buffering Systems Adapting to pH

    • Connection to biochemical reactions allowing living organisms to maintain neutral pH levels through dynamic processes.

  • Henderson-Hasselbalch Equation

    • Relationship established between pH and pKa, enabling individual analysis of various amino acid behaviors under switched pH conditions.