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Enzymes

Overview

  • Enzymes are macromolecules that catalyze biochemical reactions by lowering the activation energy.

  • They are proteins, and their names typically end in '-ase'.

  • Enzymes are not consumed by the reaction; they can be reused multiple times.

Metabolism

Definition

  • Metabolism: The sum of all chemical reactions in an organism.

Metabolic Pathways

  • Metabolic pathways: A series of chemical reactions that either build complex molecules (anabolic pathways) or break down complex molecules (catabolic pathways).

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

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

Energy in Biological Systems

Types of Energy

  • Kinetic energy: Energy associated with motion. Includes thermal energy from atom/molecule movement.

  • Potential energy: Stored energy, including chemical energy available for release in a chemical reaction.

Laws of Thermodynamics

  1. First Law: Energy cannot be created or destroyed; it can only be transformed or transferred.

  2. Second Law: Energy transformations increase the universe's entropy; during transformation, some energy is lost as heat.

Importance of Free Energy

  • Free energy (ΔG) is used to determine the likelihood of reactions:

    • ΔG = ΔH - TΔS.

    • Positive ΔG indicates non-spontaneous reactions (endergonic), while negative ΔG indicates spontaneous reactions (exergonic).

Cellular Work and ATP

ATP Structure and Function

  • Adenosine triphosphate (ATP): A vital energy carrier in cells.

  • Cells use ATP to perform three types of work:

    • Mechanical: Movement.

    • Transport: Pumping substances across membranes.

    • Chemical: Synthesis of molecules.

ATP Cycle

  • ATP can be regenerated from ADP through exergonic reactions, providing energy for cellular work.

Enzyme Mechanism

Enzyme-Substrate Interaction

  • Enzymes work by forming an enzyme-substrate complex at an active site where substrates are converted to products.

  • Induced fit: Enzyme changes shape slightly to better accommodate the substrate.

Factors Affecting Enzyme Activity

  • Enzymes' activity can be influenced by:

    • Temperature: Each enzyme has an optimal temperature; higher temperatures may lead to denaturation.

    • pH: Each enzyme operates best within a specific pH range; deviations can disrupt enzyme shape and function.

Cofactors and Coenzymes

  • Cofactors: Non-protein molecules (like metals) that assist enzyme function.

  • Coenzymes: Organic cofactors (e.g., vitamins).

Enzyme Inhibitors

Types of Inhibition

  1. Competitive Inhibitors: Block substrates from binding to the active site; can be overcome by increasing substrate concentration.

  2. Noncompetitive Inhibitors: Bind to another site (allosteric site), changing the active site shape.

Regulation of Pathways

  • Allosteric Regulation: Involves non-covalent binding to regulatory sites, which alters enzyme activity.

    • Activators: Stabilize the active form, enhancing enzyme function.

    • Inhibitors: Stabilize the inactive form, reducing activity.

Feedback Inhibition

  • End products of pathways can inhibit early enzymes, preventing overproduction and recycling of resources.