Enzymes

• What are enzymes?


  Enzymes are biological catalysts that speed up metabolic reactions, both intracellular and extracellular, building or breaking down molecules. They are made of globular proteins with an active site specific in shape, due to the bonding and folding in the tertiary structure of the protein.
• What is an intracellular reaction?


  Reactions where molecules are made and retained within the cell, eg. catalase is an enzyme inside of live cells that breaks down hydrogen peroxide into oxygen and water.
• What is an extracellular reaction?


  Reaction where molecules are made and retained outside of the cell, eg. trypsin is an enzyme in in the small intestines that hydrolyses proteins.
• What is activation?


  All reactions require a certain amount of activation energy before the reaction can begin, when enzymes attach to the substrate they lower this activation energy required by providing an alternative reaction pathway that speeds up the reaction.
• What is the lock and key model?


  The substrate (key) fits complementary to the specific tertiary structure of the enzyme (lock), forming an enzyme substrate complex and producing products. The active site is fixed, and the substrate attaches with the enzyme through random collisions; the charged groups within the active site distorting the substrate and lowering its activation energy.
• What is the induced fit model?


  The enzymes active site is induced and undergoes conformational changes upon binding to their substrate in order to achieve an enzyme substrate complex. This puts strain on the bonds and lowers the activation energy, enhancing catalytic activity.
• What does anabolic mean?

  Building up simple molecules into complex.
• What does catabolic mean?


  Breaking down complex molecules into simples.
• What is competitive inhibition?


  These are molecules that are the same shape as a specific substrate and therefore complementary to the active site, binding to it and stopping the substrate from binding, slowing the reaction and forming an enzyme inhibitor complex.
• Is competitive inhibition reversible?


  Yes, if high concentrations of substrate is added, the substrate can replace the inhibitor which is removed, increasing reaction rate.
• What type of bonds do competitive inhibitors usually use?


  Non covalent bonds.
• What is a non competitive inhibitor?


  A molecule that binds to an enzymes allosteric site, causing the active site to change shape, so the substrate is no longer complementary and fewer complexes form, reducing its catalytic activity.
• Is non competitive inhibition reversible?


  No, regardless of how much substrate is added.
• What type of bonds do non competitive inhibitors usually use?


  Covalent bonds.
• What is end product inhibition?


  Regulation of a metabolic pathway by the final product of that pathway.
• How does end product inhibition work?


  The products of some reactions act as reversible inhibitors for enzymes that control reactions, so if a lot of product is present it inhibits the enzymes and causes the reaction to slow or stop; preventing resource waste and acting as a negative feedback loop.
• What is a coenzyme?


  A non-protein organic molecule that assists enzymes in carrying out their functions; direct participation.
• What is a cofactor?


  A non-protein non organic molecule or ion that is required for the activity of an enzyme; no direct participation.
• Why are coenzyme, cofactors, and prosthetic groups needed?


  Some enzyme controlled reactions require an additional non-protein molecule in order to catalyse the reaction, and they are carried from one reaction to the next in multi step pathway reactions, binding to active sites to make them complementary to substrates.
• What is a prosthetic group?


  A type of cofactor, but instead of usual cofactors, they are permanently attached to enzyme by covalent or non covalent forces.
• What is the structure of enzyme?


  They are held together by ionic, hydrogen, and disulfate bonds, and are 3D and spherical. They are sometimes tertiary but usually quaternary, as well as being soluble in water to the position of the hydrophilic and hydrophobic R groups.
• What are examples of competitive inhibitors?

  • Statins - used in the synthesis of cholesterol, an enzyme used to reduce blood cholesterol concentration.
  • Aspirin - inhibits the active site of cox enzymes, preventing the synthesis of prostaglandins and thromboxane, chemicals responsible for producing pain and fever.
• What are examples of non competitive inhibitors?

  • Proton pump inhibitors (PPIS) - treat long term indigestion by blocking enzymes from secreting hydrogen ions in the stomach, reducing the production of excess acid which can cause stomach ulcers.
  • Organophosphates - used as insecticides and herbicides to irreversibly inhibit the enzyme acetyl cholinesterase, an enzyme responsible for nerve impulse transmission, leading to muscle cramps, paralysis, and death if ingested.
• What is precursor activation?


  Enzymes often occur in an inactive form, requiring a cofactor to activate them by binding and changing the shape of the tertiary structure. This prevents the enzymes from causing damage within cells and ensures they are only used when needed.
• What is the inactive and active enzyme called.


  A precursor protein is an apoenzyme, and an activated one is a holoenzyme.
• What are the affecting factors of enzymes?

  • Temperature
  • pH
  • Substrate enzyme concetration
• How does temperature affect enzymes?


  If temperature is too low there is insufficient kinetic energy for successful substrate enzyme collisions. If it is too high the enzymes bonds will break and the tertiary structure is altered causing a change to the active site, at which point they have denatured and can no longer form complexes.
• What is a Q10 calculation?


  Q10 temperature coefficient is a measure of the rate of change of an enzyme controlled reaction as a result of increasing the temperature by 10 Degrees Celsius.
• What is the calculation of Q10?


  Q10=R2/R1

  R1 - rate of reaction at a temperature of x Degrees Celsius.

  R2 - rate of reaction at temperature (x+10) Degrees Celsius.
• What is the affect of pH on enzyme action?

  Enzymes have varying optimum pH, and if it is too high or low pH interferes with the charges in amino acids in the active site of enzymes, causing the ionic and hydrogen bonds of enzymes to break; altering the tertiary structure and shape of the active site, deeming the enzyme denatured.
• What is the affect of substrate concentration?


  If a low concentration of substrate is present, there will be a reduced number of collisions between enzymes and substrates, decreasing the rate of reaction; if this substrate concentration increases, so does the rate. At high substrate concentration the rate will plateau as all enzymes active sites are in use, and therefore saturated.
• What is the affect of enzyme concentration?


  A low enzyme concentration causes a lower rate, and increasing this concentration increases rate, as there is a higher likelihood that enzyme substrate complexes will form. At high enzyme concentration (as long as unlimited substrate isn't added) the rate again plateaus as there will be insufficient substrate to bind to.