Enzyme Action

• Enzyme


  Protein that catalyses a specific chemical reaction
• Mechanism of Enzyme Action

  1. Enzyme has an active site where specific substrates bind forming an enzyme-substrate complex

  2. Substrate collides with the enzyme's active site at the correct orientation and speed for a reaction to occur

  3. Extremes of heat or pH can change the shape of the active site, preventing substrate binding (denaturation)
• Active site of an enzyme

  • Has a specific shape to fit a specific substrate
  • When the substrate binds, an enzyme-substrate complex is formed
• Enzyme specificity


  The complementary nature between the shape of the active site on the enzyme and its substrate(s)
• The shape of the active site (and therefore the specificity of the enzyme) is determined by the complex tertiary structure of the protein that makes up the enzyme</b>
• Proteins are formed from chains of amino acids held together by peptide bonds, and the order of amino acids determines the shape of an enzyme
• Enzyme specificity


  • The enzyme catalase can bind to its substrate hydrogen peroxide as they are complementary in shape, whereas DNA polymerase is not
• The enzyme-substrate complex


  1. An enzyme-substrate complex forms when an enzyme and its substrate join together

  2. The enzyme-substrate complex is only formed temporarily before the enzyme catalyses the reaction and the product(s) are released
• Lock-and-key hypothesis


  Enzymes and substrates are rigid structures that lock into each other very precisely, like a key going into a lock
• Induced-fit hypothesis


  The enzyme and its active site (and sometimes the substrate) can change shape slightly as the substrate molecule enters the enzyme, known as conformational changes, to achieve an ideal binding arrangement
• Activation energy


  The amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed
• Enzymes


  Speed up chemical reactions by providing an alternative energy pathway with a lower activation energy, avoiding the need for extreme conditions that would otherwise kill cells