enzymes

• Enzyme


  A biological molecule that catalyzes and speeds up the rate of biological processes and reactions inside cells
• Enzymes are required for cellular processes to occur at a rate that sustains life
• Cofactor


  Additional molecules required for enzymes to function effectively and efficiently
• Apoenzyme


  An enzyme without its cofactor
• Holoenzyme


  An enzyme bound to its cofactor
• Types of cofactors


  • Metal ions
  • Organic molecules (coenzymes) formed from vitamins
• Enzymes


  • Highly specific, only bind to specific substrates and catalyze a single reaction or a set of related reactions
  • Extremely efficient, limit unwanted products
• Nearly all enzymes are proteins, but some are RNA molecules
• Enzymes are not used up or depleted in chemical reactions, they remain unchanged at the end
• enzyme require a helper molecules 


  COFACTOR

  
• The majority of the chemical reactions and biological processes that take place within the human body are governed by a class of biomolecules known as enzymes
• Virtually all enzymes are proteins, some enzymes are in fact RNA molecules
• Enzymes


  Protein molecules that assist the chemical reactions that take place within the human body
• Enzymes


  • They increase the rate of the reaction by decreasing the activation energy of that reaction
• Enzyme catalysis

  1. Reactants

  2. Transition state

  3. Products
• Enzymes


  Increase the rate of the forward reaction and the reverse reaction by decreasing the activation energy
• Enzymes do not affect the thermodynamics of the reaction, they only affect the kinetics
• Enzymes do not change the energy of the reactants or products, they only decrease the activation energy
• Enzymes are not consumed or destroyed in the reactions they catalyze, they are regenerated at the end of the reaction
• A small quantity of enzymes can catalyze many reactions because they are not consumed
• The enzyme on the product side is the same as the enzyme on the reactant side
• Enzyme reaction


  Enzyme + Substrate ⇌ Enzyme-Substrate Complex → Product
• Kinetic constants


  • K_on: Rate constant for enzyme-substrate binding
  • K_off: Rate constant for enzyme-substrate unbinding
  • K_cat: Turnover number, rate of product formation per enzyme
  • K_M: Michaelis-Menten constant, measure of substrate binding affinity
• Competitive inhibitor


  Binds to the enzyme at the same site as the substrate, competes for binding
• Effects of competitive inhibitor

  • - Increases apparent K_M (decreases substrate binding affinity)
  • No change in V_max
• Uncompetitive inhibitor


  Binds only to the enzyme-substrate complex, not the free enzyme
• Effects of uncompetitive inhibitor

  • - Decreases apparent K_M (increases substrate binding affinity)
  • Decreases apparent V_max
• Competitive inhibitors can be overcome by increasing substrate concentration, uncompetitive inhibitors cannot
• Uncompetitive inhibitor


  Binds to the enzyme-substrate complex, decreases Vmax apparent and decreases Km apparent
• Non-competitive inhibitor


  Binds to both the free enzyme and the enzyme-substrate complex, does not change Km apparent but decreases Vmax apparent
• Mixed inhibitor


  Binds to both the free enzyme and the enzyme-substrate complex, but with unequal affinity, can increase or decrease Km apparent depending on which form it prefers, decreases Vmax apparent
• How to deal with inhibitors

  1. Can't compete out uncompetitive or non-competitive/mixed inhibitors, have to dilute them out

  2. Can compete out competitive inhibitors by adding more substrate
• Competitive inhibitors typically resemble the substrate or transition state
• Allosteric inhibitors (uncompetitive, non-competitive, mixed) can bind at sites other than the active site, so their structure is harder to predict
• Binding of inhibitor


  Affects Km apparent and Vmax apparent in different ways depending on the type of inhibitor
• Mixed inhibition is a combination of competitive and uncompetitive effects, with the net impact on Km apparent depending on which binding mode dominates