Enzymes and pH Levels

Enzyme Activity and pH

• R groups of amino acids in enzymes must have appropriate charge to interact with substrate, influenced by pH.
• Enzyme activity peaks at specific optimum pH, which varies among enzymes.
• Extreme pH levels can cause enzyme denaturation, disrupting the tertiary structure and reducing activity.
• At low or high pH, enzyme activity commonly decreases due to structural changes in active proteins.

Reaction Rates

• The energy barrier for substrate conversion into products must be surpassed for reactions to proceed.
• Reaction rate is contingent upon the number of substrate molecules capable of overcoming energy gaps, influenced by free energy of activation.
• Lower activation energy increases the rate of the reaction, as more molecules acquire sufficient energy for conversion.

Michaelis-Menten Model

• The model illustrates enzyme-catalyzed reactions where enzymes form an enzyme-substrate complex (ES) that converts to product (P).
• Enzyme (E) and substrate (S) binding is reversible, represented by rate constants k1, k-1, and k2.
• Reaction velocity is dependent on substrate concentration, as demonstrated by the Michaelis-Menten equation.

Michaelis-Menten Kinetics

• Km value signifies the enzyme's affinity for its substrate; reflects concentration at which reaction velocity is half of Vmax.
• A low Km indicates high affinity, requiring lower substrate concentration for half-saturation, while a high Km indicates low affinity.

Enzyme Characteristics

• Enzymes are proteins that act as catalysts, increasing reaction rates without altering equilibrium.
• They function effectively in small quantities, are specific in action, and may require cofactors for activity.
• Enzyme kinetics is the analysis of reaction velocities in relation to substrate concentration and enzyme concentration.

Active Site and Enzyme Action

• The active site facilitates substrate binding and transformation into products through various weak interactions.
• Lock-and-key and induced-fit models explain the specificity of enzyme-substrate interactions.
• Activation energy must be overcome to reach a transition state, wherein bond formation or breakage occurs.

Enzyme Inhibition

• Inhibitors reduce enzyme activity and can be classified as reversible or irreversible.
• Competitive inhibitors bind at the substrate active site, resembling substrate structure, and can be overcome by increasing substrate concentration.
• Noncompetitive inhibitors attach elsewhere on the enzyme, altering its shape and preventing substrate fit; their effects are not reversible by adding more substrate.

Practical Applications

• Enzyme inhibitors can serve as therapeutic agents; for example:
  • Sarin, a nerve gas, inhibits acetylcholinesterase, leading to accumulation of acetylcholine and severe physiological symptoms.
  • Penicillin, an antibacterial compound, binds to bacterial enzymes to hinder cell wall synthesis, preventing bacterial proliferation.

Explore the relationship between enzyme activity and pH levels in this quiz. Understand how the charge of amino acid R groups affects substrate binding and how extreme pH can lead to enzyme denaturation. Test your knowledge on optimal pH for maximum reaction rates.