Enzymes

• Enzymes are biological catalysts made of globular proteins.
• What determines the shape of the active site ?

  The specific folding and bonding in the tertiary structure of the protein.
• What is an intracellular reaction ?

  Reaction that occurs inside the cell
• Give an example of an intracellular reaction ?

  The break down of hydrogen peroxide into oxygen and water, catalysed by catalyse.
• Give an example of extracellular reaction ?

  The hydrolysis of proteins in the small intestine, catalysed by trypsin.
• How do enzymes work?

  They lower the activation energy, this means that more molecules will have the correct activation energy when collision occurs. Therefore more successful collisions and faster rate of reaction.
• What is the difference between lock and key model and the induced model ?

  Lock and key : enzyme active site is completely complementary to substrate

  Induced fit model : The enzyme active site is able slightly change shape to mould around the substrate.
• Anabolic reaction = a reaction that requires energy and builds up large molecules from smaller ones
• Catabolic reaction = a reaction that releases energy and breaks larger molecules into smaller ones
• Which 4 conditions effect the rate of enzyme controlled reactions ?

  • Temperature
  • pH
  • substrate concentration
  • enzyme concentration
• What happens to rate at a low temp and why ?

  The rate is slow, the molecules have insufficient kinetic energy for collisions to be successful.
• What happens to enzymes activity when temperature increases above optimum and why ?

  The activity decreases as the enzymes have denatured, this is due to the increased vibrations breaking the bonds that hold the enzymes together.
• Q10 = measure of the rate of change of an enzyme-controlled reaction as a result of increasing temperature by 10 c.

  e.g if Q10=2 , then the rate doubles every 10 c
• Q10= (rate at higher temp.)/(rate at lower temp.)
• Why do enzymes denature when ph is not optimum ?

  H+ and OH- ions break the ionic and hydrogen bonds, causing the tertiary structure to break down.
• What is the effect of a low substrate or enzyme conc.?

  Slower rate of reaction as there are few collisions between the enzymes and substrate.
• V.max = all active sites are engaged in catalysis.
• What happens at an extremely high substrate concentration ?

  The rate of reaction plateaus as all active sites are in use, therefore enzymes are fully saturated.
• competitive inhibitor = binds to active site to prevent enzyme-substrate complexes forming
• Name a difference between competitive inhibitors and non-competitive ?

  Competitive inhibitors are reversible and can be corrected wth high enough substrate concentration.
• Non-competitive inhibitors = bind to the enzyme at a different site to the active site (allosteric site ). They cause the protein to change shape and therefore altering the enzymes active site
• End-product inhibitors = products of some reactions are reversible inhibitors for enzymes involved in controlling reactions.
• What is purpose of end-product inhibitors?

  Controll the reaction and prevent resources being wasted.
• Name two reversible inhibitors ?

  Competitive and end-product
• What are cofactors?

  Non-protein molecules that assist enzymes carry out their catalytic functions
• Name 3 differences between coenzymes and cofactors ?

  Coenzymes : Organic, participate in reaction, changed by reaction

  Cofactors : inorganic, does not directly participate in reaction, not changed by reaction.
• Prosthetic group = type of cofactor that is permantly attached to enzyme.
• Metabolic poisons - interfere with metabolic reactions in cells, causing cell death.
• Example of inhibitor poisons ?

  Cyanide poisoning

  inhibits vital respiratory enzyme ( cytochrome oxidase )

  no ATP created

  body cannot function = death
• Example of medical inhibitors?

  HIV Protease inhibitor

  Competitively inhibits HIV virus protease enzyme

  RNA cannot be cut into smaller pieces to be implanted into hosts DNA

  Virus canot replicate