Biochem Enzymes

• Order of reaction


  The sum of the exponents of the concentrations of the reactants in the rate equation
• First-order reaction


  The rate depends on the concentration of one reactant to the power of 1
• Doubling the concentration of a reactant in a first-order reaction

  Doubles the rate of reaction
• Half-life


  The time taken for the concentration of a reactant to reduce to half of its initial value
• Second-order reaction


  The rate depends on the square of the concentration of a reactant, meaning doubling the concentration will increase the rate by a factor of 4
• Zero-order reaction


  The reactant's concentration to the power of 0 means it does not impact the rate, and the term is removed from the reaction
• Michaelis-Menten kinetics


  In enzyme-catalyzed reactions, the rate increases with increased substrate concentration up to a specific Vmax, where all enzyme active sites are saturated
• Km


  In enzyme kinetics, a low Km value indicates high affinity between the enzyme and substrate, while a high Km value indicates low affinity
• Vmax


  In enzyme kinetics, Vmax represents the maximum rate of product formation when the enzyme is saturated with substrate
• Turnover number (Kcat)


  Calculated as Vmax divided by the total enzyme concentration, indicating the number of substrate molecules converted to product per enzyme active site per unit time
• Assumptions in enzyme kinetics include the formation of ES complex, ES being in equilibrium with free enzymes, and breakdown of ES to products being slower than formation and breakdown to Ets
• 1. intercept


  An important point on the curve in enzyme kinetics
• Kcat


  Equal to Vmax and represents the turnover number of an enzyme
• Enzyme inhibition


  Can be irreversible (covalently bound) leading to permanent enzyme inactivation, or reversible (non-covalently bound) with no permanent effect
• Enzymes can follow different orders of binding such as random (either substrate can bind first), ordered (one substrate must bind before another), or ping-pong mechanism where substrates and products are released in a specific sequence
• Vmax


  The maximum velocity of an enzyme-catalyzed reaction under saturated substrate conditions
• The breakdown of ES to products is slower than the formation of ES and breakdown to Ets, as indicated by the rate constants k1 and k-1
• 1. intercept


  An important point on the curve in enzyme kinetics, representing the x-intercept
• Formation of ES complex


  Involves the binding of enzyme (E) and substrate (S) to form an enzyme-substrate complex (ES) as an intermediate in the reaction
• Irreversible enzyme inhibition


  Enzymes are covalently bound to the inhibitor, leading to permanent enzyme inactivation
• Enzymes


  Work by reducing activation energy, increasing the rate of reaction, and allowing the formation of products to be favored
• Exergonic


  Energy-releasing reactions
• Negative standard free energy change (ΔG°)

  Indicates that the reaction is spontaneous and the formation of products is favored
• Positive standard free energy change (ΔG°)

  In the presence of a positive ΔG°, enzymes facilitate energy absorption (endergonic reactions) and determine where the equilibrium will lie
• Classes of enzymes


  • Oxidoreductases (redox reactions)
  • Transferases (transfer functional groups)
  • Hydrolases (hydrolysis of functional groups)
  • Lyases (removal of groups)
  • Isomerases (interconversion of isomers)
  • Ligases (linking molecules)
• Enzyme specificity


  Enzymes can be absolutely specific (catalyzing only one reaction), group-specific (acting on only one functional group), linkage-specific (involving only one chemical bond), or stereochemically specific (interacting with only one stereoisomer)
• Noncovalent bonds in enzyme-substrate interactions


  Weak interactions like hydrogen bonding, ionic bonds, electrostatic attractions, and van der Waals forces
• Enzyme active site


  Enzymes bind substrates at the active site, reducing activation energy and facilitating the reaction process
• Endergonic


  Energy-requiring reactions
• Temporary covalent bonds in enzyme-substrate interactions

  Enzymes form temporary covalent bonds with substrates, aiding in catalysis and reducing activation energy
• ES*


  Transition state, a non-energy peak of the curve and highly unstable
• Active site of an enzyme

  Contains amino acids that bind the substrate (binding site) and catalyze a reaction (catalytic site)
• ΔG°


  The standard free energy change in a reaction, calculated as ΔG = ΔH - TΔS
• Entropy (ΔS)


  A component of the standard free energy change (ΔG), where ΔG = ΔH - TΔS. When ΔS is greater than 0, there is more entropy
• Exothermic reactions result in less entropy
• Enthalpy


  The energy stored in bonds, playing a crucial role in determining the overall energy change in a reaction
• Positive ΔH


  Indicates an endothermic reaction, where energy is absorbed
• 100°C is equivalent to 373.15K
• Entropy (ΔS) vs Enthalpy (ΔH)

  When ΔS has a greater impact, there is more emphasis on changes in entropy
• Coenzymes


  Bind to enzymes, promoting better conformation and function