Enzymes

• Chemical reactions that occur in the body include:

  • Releasing energy
  • Digesting food
  • Repairing cell structure
  • Assembling molecules
• Example: amylase in saliva aids in digesting food
• Enzymes are catalysts that speed up chemical reactions without being used up
• Enzymes decrease the amount of energy (activation energy) needed for a reaction to occur by bringing reactants into the best position at the active site where the enzyme and substrate join
• The protein structure of enzymes is a folded 3-dimensional shape, where the shape of the active site matches the substrate
• Enzymes weaken substrate bonds, making it easier to break them and decreasing the energy needed for the reaction to occur
• Factors affecting enzymes:

  • pH: unique enzymes function at different pH levels
  • pepsin: in stomach at pH 1.5
  • lipase: in intestines at pH 8.0 (basic)
  • catalase: in digestive organelles peroxisomes at pH 7
  • Temperature: enzymes function best at the temperature of the organisms (e.g., human enzymes work best at 37°C)
• Competitive inhibitor interferes with the active site of an enzyme, preventing the substrate from binding
• Temperature influences the rate of enzyme-catalyzed reactions
• Enzyme inhibitors control enzymes, allowing them to be turned on or off:

  • Non-competitive inhibitors: molecules that bond to the enzyme, changing its shape so the substrate cannot bind, rendering the enzyme inactive
• Too much product can inhibit the enzyme from functioning and slow down the rate of reaction until the amount is reduced again
• Noncompetitive inhibitor changes the shape of the enzyme so it cannot bind to the substrate (noncompetitive inhibition)
• Enzyme inhibition can slow down reactions, with feedback inhibition stopping enzyme reactions when a certain amount of product is reached