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.