Enzymes

• Fluctuations in pH can disrupt the formation of hydrogen and ionic bonds between polypeptide chains, therefore affecting the formation of the secondary and tertiary protein structures.
• Activation energy is the energy required to bring about a reaction.
• The active site is the region of the enzyme into which the substrate fits to catalyse a reaction.
• Enzymes lower activation energies by providing an alternative pathway for reactions to occur.
• A competitive inhibitor is a substance that binds to the active site of an enzyme to directly interfere with its functions.
• The term 'complementary' refers to the concept that the shape of an enzyme's active site is specific to the shape of the substrate.
• An enzyme is a protein that acts as a catalyst and alters the speed of a biochemical reaction.
• The lock-and-key model suggests that the active site of an enzyme has a fixed structure, while the substrate must fit perfectly into it.
• The active site of an enzyme can be altered through mutations or chemical modifications.
• In the induced-fit model, the active site changes slightly when the substrate enters, allowing them to interact more effectively.
• Competitive inhibition occurs when an inhibitor competes with the substrate for binding to the active site of the enzyme.
• Inhibitors are molecules that prevent enzymatic activity from occurring.
• Noncompetitive inhibition involves the formation of a complex between the inhibitor and the enzyme, which changes the conformation of the active site and prevents substrate binding.
• Noncompetitive inhibitors bind at another location on the enzyme, altering its conformation and preventing substrates from reaching the active site.
• The enzyme-substrate (ES) complex is formed when the substrate is acted upon by the enzyme and held in its active site.
• Enzymes can be denatured or unfolded if exposed to extreme temperatures, pH levels outside their optimal range, or high concentrations of detergents.
• Denaturation causes the loss of tertiary structure and disrupts hydrogen bonds, leading to the separation of amino acids into individual chains.
• During denaturation, the secondary structures of proteins such as alpha helices and beta sheets break down, resulting in random coils.
• Denaturation causes the loss of tertiary structure and function of proteins.
• The induced fit model proposes that the active site forms as the enzyme and substrate interact because the enzyme is flexible and moulds itself around the substrate molecule.
• Inhibitors are molecules that reduce the rate of an enzyme-catalysed reaction.
• Kinetic energy is the energy an object has when in motion.
• The lock and key model proposed that a particular substrate will only fit into the active site of a particular enzyme which has a perfectly complementary shape.
• Enzymes have specific shapes called active sites where they bind with their substrates.
• A catalyst increases the speed at which a chemical reaction occurs without being used up during the process.
• Metabolism is the sum of all chemical reactions that take place in living organisms.
• A non-competitive inhibitor binds to the enzyme somewhere other than the active site and alters its shape to inhibit substrate molecules from occupying it.
• Non-competitive inhibitors are not affected by increasing concentrations of substrate because they do not compete directly with the substrate for the active site.
• pH is the measure of the hydrogen ion concentration of a solution.
• The rate of reaction is how long it takes for the particular event to run its course.
• The term 'specific' refers to the how restrictive the enzyme is in its choice of substrate.
• A substrate molecule is a substance that is acted upon or used by another substance or process.
• Enzymes act as biological catalysts because they physically bring reactants closer together, increasing the frequency of collisions. This lowers the amount of energy needed because collisions can occur more frequently and efficiently. Therefore, reactions are sped up.
• The roles of proteins in the body:

  • enzymes (e.g. amylase)
  • structure(e.g. collagen in tendons/ligaments)
  • hormonal signalling (e.g. insulin in the blood)
  • contractile (e.g. actin/myosin)
  • storage (e.g. albumen)
  • defence (e.g. antibodies)
  • transport (e.g. haemoglobin)
• pH Affecting Enzyme Action:

  • all enzymes have an optimum pH as well as temperature; most work best at pH 7 but some work best at pH 2 (e.g. pepsin in the stomach)
  • above and below the optimum pH for each enzyme the H+ and OH- ions disrupt the ionic and hydrogen bonds holding the enzyme's tertiary structure in place
  • at extremes of pH the active site changes shape and no more ES-complexes can be formed as the substrate no longer fits; the enzyme is permanently denatured and the reaction stops
• Temperature Affecting Enzyme Action:

  • as temperature increases so does the rate of reaction: there is more kinetic energy = molecules move faster, increasing the number of collisions and the number of ES-complexes formed
  • each enzyme has an optimum temperature; once this has been reached increasing the temperature further decreases the rate of reaction
  • at high temperatures, the enzyme molecules vibrate too much and the bonds in the 3° are broken; the active site changes shape and the substrate no longer fits so the enzyme is permanently denatured and the reaction stops
• Substrate Concentration Affecting Enzyme Action:

  • increasing the substrate concentration increases the rate of reaction as there are more substrate molecules
  • more collisions so more ES-complexes formed
  • the rate of reaction will slow as the enzyme concentration becomes the limiting factor; when all the active sites are occupied (saturation point) increasing the substrate concentration will have no further effect on the rate
• Enzyme Concentration Affecting Enzyme Action:

  • increasing enzyme concentration increases the number of active sites available for the substrate to collide with
  • more ES-complexes form
  • the rate of reaction increases until the substrate concentration becomes the limiting factor as there are more enzymes than substrate molecules
• Enzymes:

  • are globular proteins
  • catalyse biochemical reactions
  • lower the activation energy of a reaction
  • can be re-used repeatedly
  • have a tertiary structure which creates the active site
• The Lock and Key Hypothesis explains the concept of an enzyme's active site being a rigid receptacle, allowing only a perfectly complementary substrate molecule to fit inside. However, this is now outdated and disproven by the discovery of the flexible structure of enzymes.