enzymes

• Conditions for a chemical reaction to occur:

  • Reacting particles need to collide with enough energy to break the bonds (activation energy)
  • Particles must collide so that the correct atoms come into contact with one another
• At any given temperature, a certain proportion of particles have enough energy to satisfy the activation energy, which increases with temperature
• Catalysts decrease the energy needed to break bonds, lowering activation energy and allowing more particles to react, speeding up the reaction; catalysts are not consumed during reactions
• In living things, catalysts are proteins called enzymes, which allow chemical reactions to occur at a fast enough rate at body temperature
• Enzymes are biological catalysts that speed up reactions by lowering activation energy; they are specific for a particular reaction and are not consumed or altered in the reaction
• Enzymes have a specific shape that allows them to combine with only one particular substrate, forming an enzyme-substrate complex at the active site
• Two models describe enzyme function:

  1. Lock-and-key model: enzyme shape (key) is complementary to substrate shape (lock), fitting exactly

  2. Induced-fit model: enzyme and substrate form weak bonds, causing enzyme shape to change to fit substrate
• higher concentration of enzymes will have a higher rate of reaction because there are more enzyme molecules to influence reactants
• the body can control which reactions occur and the rate by regulating the type and number of enzymes present
• increase substrate concentration increases the rate of reaction because there will be more substrate molecules coming into contact with enzyme molecules
• increasing substrates beyond a certain point will have no affect as the enzymes become saturated
• the products of reactions must be continually removed otherwise the rate of reactions will slow because it becomes more difficult for the substrates to make contact with enzymes
• increase in temperature will increase the rate of most chemical reactions but only within a certain temperature range. optimum temperature is between 30 - 40
• beyond 45 - 50 enzymes change structures and are denatured
• enzymes are sensitive to the pH of their environment
• cofactors are certain ions or non-protein molecules that are required for enzymes to start catalysing reactions. they change the shape of the active site so enzymes can combine with the substrate
• coenzymes are non-protein organic molecules that are cofactors for enzymes
• enzyme inhibitors are substrates that slow or stop the enzyme's activity
• inhibitors are used by cells to control the reactions that take place so products are produced in specific amounts