Enzymes Notes

Enzymes Overview

• Enzymes are biological catalysts that speed up biochemical reactions without being consumed.

• Substrates are reactants acted upon by enzymes, which convert them to products.

• General equation: enzymes + substrates → products

Role of Enzymes in Metabolism

• Metabolism: Network of chemical reactions in living organisms.

  • Reactions can be intracellular (inside cells) or extracellular (outside cells).

  • Metabolic pathways usually involve multiple steps with specific intermediates.

• Enzymes exhibit specificity, catalyzing only specific reactions, requiring various enzymes for different reactions.

Metabolic Processes

• Anabolism: Reactions that build larger molecules from smaller ones (requires energy).

  • Example: Photosynthesis (conversion of CO2 and H2O to glucose).

  • Other examples: Protein synthesis, DNA synthesis, polysaccharide synthesis.

• Catabolism: Reactions that break down larger molecules into smaller ones (release energy).

  • Example: Cellular respiration of glucose into CO2 and H2O, producing ATP.

Enzyme Structure and Function

• Enzymes are globular proteins with specific 3D structures.

  • Active Site: Region where substrates bind; specific shape complements substrate.

  • Binding leads to substrate transformation and release of products.

  • Key steps in enzyme-substrate interaction include collision, binding, and product release.

Influence of Molecular Motion

• Molecular motion impacts enzyme and substrate interactions:

  • Reaction rate increases with temperature (increased kinetic energy) and substrate concentration.

  • Three scenarios: Enzyme larger than substrate, substrate larger, or enzyme immobile in membranes.

Factors Affecting Enzyme Activity

• Temperature: Higher temperatures increase reaction rates but can denature enzymes.

• pH Levels: Most enzymes function optimally at around pH 7; deviations lead to denaturation by altering active site shape.

• Substrate Concentration: Increased concentration raises reaction rates until active sites become saturated.

Activation Energy

• Substrates must reach a transition state requiring activation energy to react.

• Enzymes decrease the activation energy needed, facilitating quicker reactions.

Types of Enzymes

• Intracellular Enzymes: Synthesized within the cell (e.g., hexokinase in glycolysis).

• Extracellular Enzymes: Synthesized outside the cell (e.g., digestive enzymes).

Enzyme Inhibition

• Inhibitors can decrease enzymatic activity.

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

  • Non-Competitive Inhibitors: Bind to the allosteric site, altering enzyme shape.

Feedback Inhibition

• Metabolic pathways are regulated by feedback inhibition to prevent overproduction.

  • End-products inhibit the first enzyme in a pathway by binding to its allosteric site.

Mechanism-Based Inhibition

• Irreversible inhibitors form permanent complexes with enzymes, rendering them inactive (e.g., heavy metals, sarin gas affecting acetylcholinesterase).

• Example: Penicillin inhibits transpeptidase in bacteria, weakening cell walls and causing bacterial cell lysis.