Understanding Enzymes: Catalysis and Function

Enzymes

• Enzymes are protein catalysts which speed chemical reactions in cells at low temperatures by reducing activation energy.
• Enzymes remain unchanged after reactions and can be reused.

Key Terms

• Catalyst: Increases reaction rate without being altered.
• Enzyme: A protein catalyst.
• Substrate: A molecule acted upon by an enzyme.
• Active Site: Area of an enzyme that binds with a substrate.
• Cofactor: An inorganic ion that helps an enzyme bind.
• Coenzyme: An organic molecule synthesized from a vitamin aiding enzyme binding.
• Competitive Inhibitor: A molecule that competes with the substrate for the enzyme's active site.
• Feedback Inhibition: The inhibition of an enzyme in a metabolic pathway by the pathway's final product.
• Precursor Activity: Activation of the last enzyme in a metabolic pathway by the initial substrate.
• Allosteric Activity: A change in an enzyme due to molecule binding.

Enzyme Identification

• Enzymes are identified by the suffix "-ase."
• Carbohydrases break down carbohydrates.
• Sucrase hydrolyzes sucrose into glucose and fructose.
• Proteases break down proteins.
• Lipases act on lipids.

Enzyme Reactions

• Enzymes increase reaction probability by bringing substrate molecules together.
• Enzymes have folded surfaces which trap and align substrate molecules.
• Emil Fischer proposed the "lock-and-key model" in 1890.
• The "induced-fit model" suggests the active site's shape changes slightly when substrate molecules are trapped to make the fit tighter.

Factors Affecting Enzyme Reactions

• pH: Enzymes function best within specific pH ranges.
• Pepsin operates best in acidic conditions.
• Trypsin is most effective in a basic medium.
• pH affects the folds of protein molecules, altering the active site and reaction.
• Substrate Molecule Concentration: Greater number of substrate molecules increases the number of collisions, and increases reaction rate up to a limit.
• Temperature: Reaction rates increase as temperature increases, but drop if temp is too high
• Enzymes change shape or denature at high temperatures.
• Enzyme shape change affects the formation of an enzyme-substrate complex.
• High fevers can be dangerous due to temperature's effect on enzymes.
• Homeotherms maintain optimal temperatures for reactions.

Enzyme Regulation

• Metabolic pathways proceed in orderly sequences of chemical reactions.
• Production of chemicals is regulated.
• Feedback inhibition slows reaction rate and prevents final product accumulation.
• The final product combines with the regulatory site of the enzyme.
• Precursor activity speeds up final product formation.
• Both feedback inhibition and precursor activity involve molecule binding and are called allosteric activity.