1.5 Enzymes

• The most important part of an enzyme is the active site.
• An enzyme is a biological catalyst that speeds up reactions by lowering the activation energy by bending the bonds in the substance.
• Temperature, pH and concentration affect how fast enzymes can work.
• Lipase, protease, amylase are examples of enzymes.
• Carbohydrase is an enzyme that breaks down carbohydrates into simple sugars.
• Lipase is an enzyme that breaks down lipids into fatty acids and glycerol.
• Protease is an enzyme that breaks down proteins into amino acids.
• Amylase is an enzyme that breaks down starch into glucose.
• A substrate binds to the active site of an enzyme to form an enzyme-substrate complex.
• After an enzyme-substrate complex is formed, the unaffected enzyme releases the products.
• Activation energy is the energy required to start a reaction.
• The lock and key model doesn't show that the enzyme's active site changes slightly so the substrate can fit.
• The induced fit model shows how an enzyme's active site changes shape slightly so the substrate will fit.
• When an enzyme binds to a substrate, it is called an enzyme-substrate complex.
• The shape of the active site is complementary to the shape of the substrate.
• The tertiary structure of a protein defines the shape of the active site.
• The substrate is broken down into its products and is released from the enzyme.
• When an enzyme is denatures, the ionic bonds, hydrogen bonds and disulphide bridges in the tertiary structure are broken, so the shape of the active site changes, so can no longer bond to form enzyme-substrate complexes.
• How does pH affect enzymes?

  H+ ions disrupt the ionic bonds, hydrogen bonds, and disulphide bridges in the tertiary structure, this means the active site and substrate are no longer complementary and do not join. This means few enzyme-substrate complexes are formed.
• The limiting fact limits the rate of reaction (can be either the enzyme concentration or the substrate concentration).
• As enzyme concentration increases, more active sites become available. This means more enzyme-substrate complexes can be formed, so rate of reaction increases.
• Enzymes can be stopped from working by inhibitors.
• We can control the enzyme activity to control the amount of product made, or amount of substrate used.
• Many poisons inhibit important respiratory enzymes, causing cell death.
• A competitive inhibitor blocks the enzyme's active site.
• Non-competitive inhibitors change the shape of the active site by binding to the allosteric site.