1.3 Protein Structure and Enzyme Function

• Active site

  Region on an enzyme with a specific shape to fit certain molecules
• How enzymes work

  They work on anabolic reaction (joining molecules together) or catabolic reaction (separating molecules)
• Enzyme-substrate complex

  An enzyme bonded to its substrate
• Enzymes lower activation energy


  Lowering the amount of energy required for a reaction to begin, increasing reaction rate
• Enzyme-substrate interaction

  When a substrate binds to an enzyme, the active site changes shape slightly to improve the fit (induced-fit model)
• Enzymes

  • Proteins that catalyze (speed up) chemical reactions
  • Have a region called the active site with a specific shape to fit certain molecules
  • Each enzyme has a specifically shaped active site to match its substrate
• Factors affecting enzyme activity
• Induced fit model

  When an enzyme and substrate match, the enzyme changes shape slightly for a better fit
• Substrate and enzyme example

  • sucrase (enzyme) breaks down sucrose (substrate) molecule
• Substrate

  A molecule that an enzyme acts on
• Denaturing


  The altering of an enzyme's shape, rendering it non-functional
• Activation energy

  The initial energy input needed to start a reaction
• Factors affecting enzyme activity

  • Temperature
  • pH
  • Inhibitors
  • Concentration of enzymes and substrates
• Optimum temperature


  The temperature at which an enzyme works best
• Concentration of enzymes and substrates

  • Rate of reaction is low with fewer enzymes due to fewer active sites
  • If substrate concentration is low, enzymes will run out of molecules to bind to, resulting in a slower reaction
  • Insufficient enzyme or substrate becomes a limiting factor, limiting the speed of the chemical reaction
• Inhibitors

  • Competitive inhibitors bind to the active site, preventing substrate binding and reaction
  • Non-competitive inhibitors bind to the enzyme, changing its shape so the substrate no longer fits