Enzyme Mechanisms and Function

Enzyme Mechanisms and Function

• Enzymes are biological catalysts, speeding up reactions essential for life that would otherwise proceed too slowly.
• Catalysts change reaction rates without being consumed; enzymes are unaffected and reusable.
• Almost all enzymes are proteins (tertiary or quaternary structure).
• Enzymes lower activation energy, enabling reactions to occur.
• They are not consumed in the reaction.
• Enzymes have active sites that bind specific substrates, forming enzyme-substrate complexes.

Enzyme Types

• Simple enzymes are composed only of proteins.
• Complex enzymes need a cofactor besides the protein component.
  • Apoenzyme: inactive form lacking the cofactor.
  • Holoenzyme: active form with the cofactor.

Cofactors and Coenzymes

• Cofactors are inorganic metal ions (e.g., Zn, Fe, Cu), crucial enzyme function.
• Coenzymes are organic molecules, often derived from water-soluble vitamins (e.g., NAD+ from niacin).

Enzyme Components and Function

• Enzymes act on substrates at their active sites.
  • Substrate: the reactant acted upon by the enzyme.
  • Active site: a binding pocket with a catalytic center, converting substrate to product.
• The induced fit model describes how enzyme shape changes upon substrate binding for a tighter fit, optimal catalysis.

Enzyme Specificity

• Reaction Specificity: Enzymes catalyze one specific chemical reaction (e.g., sucrase hydrolyzes sucrose).
• Forward and Reverse Reactions: Many metabolic enzymes catalyze reactions in both directions.
• Substrate Specificity: Enzymes recognize a particular set of substrates essential for their specific reactions (e.g., sucrase binds sucrose, water, glucose, and fructose).

Enzyme Names

• Enzyme names typically end in "-ase".
• The root signifies the reaction type or product generated. (e.g., ATPase).

Exothermic Reactions

• Exothermic reactions release energy during reaction
• Requires energy input to break bonds in reactants prior to releasing energy.
• Energy comes from thermal sources.

Activation Energy

• Activation energy (EA) is the energy needed to surpass the transition state, where reactant molecules become unstable.
• Thermal agitation increases molecular speed and collision strength, facilitating reactions.
• Transition state is peak of activation energy.
• Bonds are eventually broken, and new ones form.

Change in Free Energy (ΔG)

• ΔG is the difference in free energy between products and reactants.
• ΔG is negative for exothermic reactions.
• Enzymes do not alter ΔG. but they help reactions reach equilibrium faster.

Factors Affecting Enzyme Activity

• Enzymes lower activation energy (EA) by facilitating the transition state.
• Reduced temperature requirements speed up reaction rates.
• Limitations:
  • Substrate concentration
  • Temperature
  • pH
  • Cofactor availability.

Substrate Concentration

• Low substrate concentration: rate directly correlates with substrate concentration.
• High substrate concentration: enzyme saturation occurs, and increasing substrate concentration has little effect on rate other than enzyme saturation.

Temperature

• Higher temperature increases enzymatic reaction rates due to increased molecular movement and collisions.
• Optimal temperature exists for each enzyme.
• High temperatures cause enzyme denaturation, halting enzyme activity.

pH

• Each enzyme has an optimal pH range.
• Deviating from optimal pH disrupts the active site causing enzyme denaturation. and halts activity.
• Stomach enzymes (e.g., pepsin) function optimally at low pH, whereas intestinal enzymes (e.g., trypsin) function optimally at higher pH.

This quiz explores the mechanisms and functions of enzymes, the biological catalysts essential for life. It delves into enzyme types, their structures, and the roles of cofactors and coenzymes in enzyme function. Test your knowledge on how enzymes facilitate reactions and their importance in biological processes.