BIOCHEM LEC ENZYMESS

• What Affects Enzyme Activity?

  • Three factors:
  • 1. Environmental Conditions
  • 2. Cofactors and Coenzymes
  • 3. Enzyme Inhibitors
• Environmental Conditions


  • Concentration of the Substrate
  • Concentration of the Enzyme
  • Extreme Temperature
  • pH (most like 6 - 8 pH near neutral)
• Substrate concentration: Non-enzymic reactions


  The increase in velocity is proportional to the substrate concentration
• Substrate concentration: Enzymic reactions


  • Faster reaction but it reaches a saturation point when all the enzyme molecules are occupied
  • If you alter the concentration of the enzyme then Vmax will change too
• Concentration of the Enzyme


  The increase in velocity is proportional to the enzyme concentration
• The effect of temperature


  • Graph showing enzyme activity at different temperatures
• The effect of pH


  • Graph showing optimum pH values for Trypsin and Pepsin
• Cofactors and Coenzymes


  Inorganic substances (zinc, iron) and vitamins are sometimes needed for proper enzymatic activity
• Enzymes


  Proteins with catalytic properties due to their power of specific activation
• Example of Cofactor


  • Iron must be present in the quaternary structure of hemoglobin in order for it to pick up oxygen
• Chemical reactions


  1. Need an initial input of energy = the activation energy

  2. During this part of the reaction the molecules are said to be in a transition state
• Competitive inhibitors


  Chemicals that resemble an enzyme's normal substrate and compete with it for the active site
• Noncompetitive inhibitors


  Inhibitors that do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site
• Enzymes


  • Can increase the rate of reactions without increasing the temperature
  • They do this by lowering the activation energy
  • They create a new reaction pathway "a short cut"
• Enzymes


  • Most are proteins (tertiary and quaternary structures)
  • Act as catalysts to accelerate a reaction
  • Not permanently changed in the process
• Enzymes


  • Are specific for what they will catalyze
  • Are reusable
  • End in -ase (e.g. Sucrase, Lactase, Maltase)
• How enzymes work


  Enzymes work by weakening bonds which lowers activation energy
• Without enzyme


  Higher free energy of activation
• With enzyme


  Lower free energy of activation
• Enzyme-substrate complex


  The substance (reactant) an enzyme acts on is the substrate
• Active site


  A restricted region of an enzyme molecule which binds to the substrate
• Cofactors


  • Additional non-protein molecules needed by some enzymes to help the reaction
  • Tightly bound cofactors are called prosthetic groups
  • Cofactors that are bound and released easily are called coenzymes
  • Many vitamins are coenzymes
• Lock and key hypothesis


  • Fit between the substrate and the active site of the enzyme is exact, like a key fits into a lock very precisely
  • Temporary structure called the enzyme-substrate complex formed
  • Products have a different shape from the substrate
  • Once formed, they are released from the active site leaving it free to become attached to another substrate
• Enzyme may be used again

  Enzyme-substrate complex forms, then products are released
• Induced fit


  A change in the configuration of an enzyme's active site (H+ and ionic bonds are involved), induced by the substrate