Enzyme Regulation and Function

Enzyme Regulation and Metabolic Control

Allosteric Regulation

  • Enzymes are regulated by binding molecules at allosteric sites (specific binding sites that are not the active site).
  • Allosteric binding changes the enzyme's shape, which can either stimulate or inhibit enzyme activity.
Feedback Inhibition
  • In feedback inhibition, the end product of an enzymatic pathway inhibits an enzyme earlier in the pathway by binding to its allosteric site.
  • This mechanism increases the efficiency of the pathway by turning it off when the end product accumulates.
  • Efficient energy use is achieved when the product of one step becomes the reactant for the next.
  • Feedback mechanisms are triggered by changes in molecular concentrations to maintain homeostasis.

Cellular Respiration and Fermentation

  • Summary Equation of Cellular Respiration:
    • Understanding the source and fate of reactants and products is crucial.
  • Distinction between Fermentation and Cellular Respiration:
    • Key differences exist between these two processes.
  • Glycolysis:
    • An ancient, oxygen-independent process shared by all life forms.
    • Glycolysis oxidizes glucose, producing ATP, NADH, and pyruvate.
  • Pyruvate Transport:
    • Pyruvate moves from the cytosol into the mitochondria for further processing.
    • It is then introduced into the citric acid (Krebs) cycle.
  • Electron Transport Chain and Chemiosmosis:
    • Electrons from NADH and FADH2 are passed to electron acceptors.
    • This process produces ATP through chemiosmosis.
  • Mitochondrial Membrane, Proton Gradient, and ATP Synthase:
    • These components play vital roles in ATP generation.

Cofactors and Coenzymes

  • Many enzymes require nonprotein helpers called cofactors for proper function.
  • Cofactors include metal ions like zinc, iron, and copper, which facilitate catalysis.
  • Coenzymes are organic cofactors; vitamins are examples of coenzymes.

Enzyme Regulation

  • Enzymes are regulated by being "turned off" when there is too much product and "turned on" when more product is required.
Competitive Inhibitors
  • Competitive inhibitors compete with the substrate for the active site.
  • They can bind reversibly or irreversibly.
  • Many poisons act as competitive inhibitors.
  • Competitive inhibitors reduce the efficiency of the enzyme.
  • They are often similar to the normal substrate molecule.
Noncompetitive Inhibitors
  • Noncompetitive inhibitors bind to another part of the enzyme, not the active site.
  • Binding changes the enzyme's shape, rendering the active site nonfunctional.
Enzyme and Substrate Concentration
  • Enzyme and substrate concentrations affect the efficiency of enzymatic reactions.
  • Assuming abundant substrate, increasing enzyme concentration increases the final product.
  • If enzyme concentration is constant, increasing substrate concentration increases the reaction rate until the enzyme is saturated.

Visual Representation Analysis

  • Typical Enzyme Reaction Graph:
    • The graph illustrates the amount of product over time.
  • Effect of Increased Enzyme Concentration:
    • Increasing enzyme concentration will increase the rate of product formation, resulting in a steeper curve on the graph.
  • Effect of Increased Substrate Concentration:
    • Increasing substrate concentration will increase the rate of product formation until the enzyme is saturated, after which the rate will plateau.