1.5 Enzymes

• Key ideas

  • Globular proteins
  • Specific tertiary structure
  • intracellular/ extracellular
  • Biological catalysts
• Characteristics

  • Sensitive to temperature
  • High molecular weight
  • Sensitive to pH
  • Generally specific reactions
  • Some can do the reverse reaction
• Lock and key model


  Enzyme binds to substrate to form an enzyme-substrate complex

  
• Induced fit model


  • Considers that proteins have some 3D flexibility
  • substrate binds to active site
  • induces enzyme to change shape to form an exact fit
  • Reactions take place after induced fit
• cofactor


  substance that must be present for enzyme controlled reactions to take place at the appropriate rate
• coenzyme


  organic molecule that binds either just before or at the same time as the substrate that helps reactions take place in sequence
• Prosthetic group


  inorganic ion that is a permanent part of the enzyme contributing to its 3D shape.
• Inorganic ion


  either binds to enzyme or substrate to help form the enzyme-substrate complex
• Activation energy


  Energy needed to get a reaction started
• Temperature and molecular collisions

  -low temp= low energy =low movement= less successful collisions

  -High temp= high energy= high movement= more successful collisions
• Denaturing


  High temps=vibrations break hydrogen bonds, active site changes, substrate can't bind and form enzyme-substrate complexes
• Enzymes and pH


  changes in pH affects ionic and hydrogen bonds
• Calculation for pH of solution based on hydrogen ion concentration


  pH=-log^10(H+)
• Effect of substrate concentration on enzyme activity

  • low substrate concentration=low product concentration
  • reaches v max
• The rate of enzyme concentration

  rate of reaction and enzyme concentration are directly proportional
• Enzyme inhibitiors


  any substance that interferes in a detrimental way with enzyme activity
• How do competitive inhibitors work?

  • compete for the active site, occupies it
  • increase concentration of substrate to decrease effect of inhibitor

  
• How do non-competitive inhibitors work?

  • attach to allosteric site
  • Alters enzyme's active site temporarily, substrate can't bind
  • Cannot be overcome

  
• Examples of competitive inhibitors


  • penicillin
  • Protease inhibitor
  • Ethanol
• Examples of non-competitive inhibitors


  -ibuprofen
• Examples of irreversible inhibitors acting as poisons


  • snake venom
  • Cyanide