2.4 Enzymes

• enzyme: a biological catalyst that speeds up the rate of a reaction by lowering activation energy, without being used up at the end.
• anabolic enzymes build up molecules from smaller ones, while catabolic enzymes break down molecules into smaller ones
• enzymes will only speed up certain reactions as they are what?


  specific
• what processes are enzymes used for?

  respiration, protein synthesis, digestion, photosynthesis, DNA replication.
• the shape of the active site is complementary to the substrate molecule, giving enzymes their specificity.
• intracellular enzymes: enzymes that are work inside the cell.
• extracellular enzymes: enzymes that are secreted by an organism and are found outside the cell. this includes fungi (saprotrophic) secreting digestive enzymes then re absorbing the nutrients.
• cofactor: a molecule that is required for the enzyme to take place at an appropriate rate.
• a prosthetic group is an example of a cofactor that is part of the enzyme structure, held by covalent bonds. (permanently bound).
• Other cofactors can be mineral ion cofactors or organic coenzymes. These are not permanently bound to the enzyme structure.
• co-substrates join with the substrate to form the correct shape to bind with the active site and create enzyme substrate complexes.
• The chloride ion is a cofactor of amylase
• many coenzymes are water-soluble vitamins
• induced fit model: the active site of an enzyme changes shape to fit the substrate
• what factors affect enzymes?

  temperature, pH, enzyme concentration and substrate concentration.
• temperature coefficient: the measure of how much the rate of a reaction increases with a 10 degree celsius rise in temperature.
• optimum temperature: the temperature at which the maximum rate of reaction occurs
• Q10 = rate at temperature (t + 10) / rate at temperature. The answer is usually 2 for enzymes.
• Describe the effect of temperature on enzyme activity

  Gradual increase at lower temperatures, sharp decline after v-max (optimum).
• explain the effect of temperature on enzyme activity

  collissions are less frequent at lower temperatures so product release is decreased. As temperature increases, molecules move faster as enzymes and substrate gains kinetic energy transferred from heat. thus collisions are more frequent and more product is released.
• above a certain temperature, bonds holding the enzyme structure break and the enzyme changes shape. the active site is now no longer complementary to the substrate so the enzyme is denatured.
• the effect of temperature on enzyme (amylase) activity test: IV - temperature of the water baths, DV - the time taken for starch to be broken down.
• buffer: chemicals that help reduce pH fluctuations.
• most enzymes have an optimum pH of 7, so the graph looks sort of like a bell.
• serial dilution technique: used to dilute the concentration of a solution using water. dilution factor can be going down by 10 or half.
• effect of enzyme concentration on rate: proportional. plateaus because the substrate concentration becomes the limiting factor.
• effect of substrate concentration on rate: proportional, plateaus because enzyme concentration has become the limiting factor.
• The saturation point: the point at which there is so much of somethings that no more can be added successfully.
• competitive inhibitor: similar to the shape of the substrate but doesn't react with it. It competes with the real substrate for binding sites on the active site.
• If the concentration of substrate is higher, it can outcompete the competitive inhibitor.
• non-competitive inhibitors bind to an allosteric site (different from the active site).
• Non-competitive inhibition causes a permanent change in the structure of the enzyme (active site shape), making it less effective.
• Non-competitive inhibitors have a greater inhibitory effect, as outcompeting using substrate concentration does not work, as the shape of the active site is no longer complementary.
• end production inhibition: when the product produced by an enzyme inhibits the enzyme from making more product.
• enzyme inhibition can be used in poisons and medicinal drugs: penicillin inhibits the enzyme that produces bacterial cell walls, preventing cell division.