Chapter - 6 (1)

ENERGY and METABOLISM

Chapter Overview

• Focuses on the relationship between energy and metabolism in living organisms.

The Energy of Life

• Living cells operate as chemical factories with thousands of simultaneous reactions.

• Cells extract, convert, and apply energy to perform various work functions.

• Some organisms exhibit bioluminescence, converting energy into light (e.g., fluorescent frog).

Metabolism

• Defined as the total chemical reactions within an organism, a key emergent property of life.

• Involves specific reactions at the cellular level.

• Governed by two main factors:

  • Direction: Influenced by concentration and available energy.

  • Rate: Catalysts (enzymes) speed up reactions.

  • Example reaction: aA + bB ↔ cC + dD.

Metabolic Pathways

• Definition: A series of reactions beginning with a specific molecule and ending with a product, with each step catalyzed by an enzyme.

• Types of Pathways:

  • Catabolic pathways: Release energy by breaking down complex molecules.

  • Anabolic pathways: Consume energy to build complex molecules from simpler ones.

• Example: The conversion of α-ketoglutarate and NH4+ into glutamate.

• Bioenergetics: Study of energy flow in living organisms.

Energy

• Defined as the ability to promote change; it exists in various forms:

  • Kinetic Energy: Associated with movement.

  • Potential Energy: Due to structure or location (e.g., chemical energy).

  • Thermal Energy: Kinetic energy related to atomic/molecular movement.

  • Heat: Thermal energy transferred between objects.

  • Light: A form of energy that can perform work.

• Thermodynamics: Study of energy transformations.

  • Units of Energy:

    • Calorie: Heat required to raise 1g of water by 1°C.

    • Kilocalorie: 1000 calories.

    • Joule: 0.239 calories.

Redox Reactions

• Oxidation-reduction reactions transfer energy:

  • Oxidation: Loss of an electron.

  • Reduction: Gain of an electron.

• These reactions are always paired.

Laws of Thermodynamics

1. First Law: Conservation of energy principle (energy cannot be created or destroyed).

2. Second Law: Energy transfer increases entropy (disorder).

   • Open Systems: Exchange energy and matter with surroundings.

   • Isolated Systems: No exchange occurs.

   • Note: Organisms are open systems.

Free Energy Changes

• Changes in free energy (G) dictate reaction direction and spontaneity:

  • Entropy: Measure of disorder, cannot be harnessed to perform work.

  • Variables:

    • H: Enthalpy (total energy).

    • G: Free energy (usable energy).

    • S: Entropy (unusable energy).

    • T: Absolute temperature (in Kelvin).

  • Equation: H = G + TS.

Spontaneous Reactions

• Occur without additional energy input and are identified by free energy changes:

  • Exergonic Reactions: ΔG < 0 (negative free energy change), spontaneous.

  • Endergonic Reactions: ΔG > 0 (positive free energy change), require energy input.

ATP Hydrolysis

• Hydrolysis of ATP releases energy (ΔG = -7.3 kcal/mole), driving cellular processes.

• Main types of cellular work:

  • Chemical Work

  • Transport Work

  • Mechanical Work

• Coupling of endergonic and exergonic reactions allows for spontaneous reactions.

Energy from Catabolism

• Catabolic processes release energy and generate ATP (exergonic).

• ATP is utilized in endergonic reactions (energy-consuming processes).

Overcoming Activation Energy

• Activation energy is the energy needed to initiate a reaction:

  • Requires destabilizing chemical bonds to reach the transition state.

• Methods of overcoming energy barriers:

  • Add large amounts of heat or use enzymes to lower activation energy.

Enzymes and Catalysis

• Catalysts: Substances that increase reaction rates without being consumed (e.g., enzymes).

• Enzymes: Protein catalysts specific to reactions in living cells.

• Activation Energy: Required to initiate bond rearrangement during a reaction.

Enzyme Specificity and Function

• The active site is where enzymes interact with substrates to form enzyme-substrate complexes.

• Enzymes have a high affinity for substrates, often described by the lock-and-key model and induced fit mechanism.

• Factors affecting enzyme activity:

  • Temperature and pH levels; enzymes often need a specific environment to function optimally.

Enzyme Regulation

Types of Inhibitors

• Competitive Inhibitors: Compete with substrates for the active site.

• Noncompetitive Inhibitors: Bind elsewhere on the enzyme, changing its shape and functionality.

Allosteric Regulation

• Allosteric enzymes exist in active and inactive forms, regulated by allosteric activators and inhibitors.

• Feedback Inhibition: The end product of a metabolic pathway inhibits an enzyme involved in its synthesis, preventing resource wastage.

• Cooperativity: A form of allosteric regulation that can amplify activity when one substrate molecule primes the enzyme for additional substrate molecules.