Introduction to Enzymes

Introduction to Enzymes

• Enzymes are biological catalysts that accelerate biochemical reactions in living organisms.
• They are typically proteins, although some RNA molecules (ribozymes) also function as enzymes.
• Enzymes increase the rate of reactions by lowering the activation energy required for the reaction to proceed.
• They are highly specific, typically catalyzing only one particular reaction.
• Enzymes are not consumed or changed by the reactions they catalyze; they remain unchanged after the reaction is complete.

Enzyme Structure and Function

• The active site is a specific region of the enzyme’s structure that binds to the substrate, the molecule on which the enzyme acts.
• The shape and chemical properties of the active site are crucial for substrate specificity.
• The interaction between the enzyme and substrate often involves weak, non-covalent bonds such as hydrogen bonds, ionic bonds, and van der Waals forces.
• The induced fit model suggests that the enzyme’s active site changes shape slightly upon substrate binding to optimize the interaction and improve the catalytic efficiency.

Factors Affecting Enzyme Activity

• Temperature: Enzymes have optimal temperatures for activity. Above or below this optimal temperature, activity decreases due to denaturing or reduced substrate interaction.
• pH: Each enzyme has a specific pH range for optimal activity. Changes in pH can disrupt the enzyme’s structure and alter the charges on amino acid residues in the active site, affecting substrate binding and catalysis.
• Substrate concentration: Increasing substrate concentration generally increases the reaction rate until the enzyme becomes saturated, and the reaction rate reaches its maximum.
• Enzyme concentration: Increasing enzyme concentration, with sufficient substrate, also increases the reaction rate up to a point, where all enzymes are functioning to capacity.
• Inhibitors: Substances that can decrease enzyme activity. Competitive inhibitors bind to the active site, blocking substrate binding; non-competitive inhibitors bind to a different site on the enzyme, altering its shape and making the active site less effective.

Enzyme Classifications

• Enzymes are grouped into six major classes based on the type of reaction they catalyze.
  • Oxidoreductases: Catalyze oxidation-reduction reactions.
  • Transferases: Catalyze the transfer of a functional group from one molecule to another.
  • Hydrolases: Catalyze the hydrolysis of a chemical bond by adding water.
  • Lyases: Catalyze the addition or removal of a group from a substrate, often forming or breaking double bonds.
  • Isomerases: Catalyze the conversion of one isomer to another.
  • Ligases: Catalyze the joining of two substrate molecules using ATP energy.

Enzyme Regulation

• Allosteric regulation: Enzyme activity is modulated by the binding of a molecule at a site other than the active site (allosteric site). This binding can either activate or inhibit the enzyme.
• Covalent modification: Enzyme activity can be regulated by the addition or removal of a chemical group (e.g., phosphorylation). This process can either activate or deactivate the enzyme.
• Feedback inhibition: The product of a metabolic pathway can inhibit the activity of an enzyme early in the pathway to prevent excessive product accumulation.

Importance of Enzymes in Biological Systems

• Enzymes are essential for the vast majority of biochemical processes in living organisms.
• They are responsible for metabolic pathways (e.g., glycolysis, Krebs cycle), providing energy and necessary materials for life.
• They catalyze various vital processes like DNA replication, protein synthesis, and cellular respiration.
• Their regulated function is crucial for maintaining homeostasis and ensuring proper cellular function.