Metabolic Pathways

• For substance 4 to bring about feedback inhibition, with which of the following would it interact?

  enzyme 1
• 4. As part of a metabolic pathway substrate X is

  converted into product Y.

  Under what circumstances would this reaction

  be reversed?

  An increase in concentration of Y and

  removal of X
• Non-competitive inhibitors affect enzyme action by

  altering the shape of the active site of the enzyme
• 7. The diagram below represents the shapes of

  an enzyme molecule and its substrate.

  Which row in the table below shows the possible

  shapes of two types of molecule that could

  inhibit the enzyme above?

  D
• catabolism?

  1. Releases energy
  2. Involves the breakdown of molecules
  3. Has reversible and irreversible steps and alternative routes
• 11. Which statement about enzyme inhibition is correct?

  In competitive inhibition, the inhibitor binds to the active site of the enzyme
• If an inhibitor which affects enzyme 2 is introduced to the system, which of the following will happen?

  X will accumulate
• Phenylketonuria (PKU) is a metabolic

  disorder which can be lethal in childhood. It is

  caused by an inability to make enzyme X, shown

  in the metabolic pathway below.

  Which substance would have to be removed

  from the diet for someone who has this

  disorder?

  Phenylalanine
• Non-competitive inhibitors affect enzyme action by

  altering the shape of the active site of the enzyme
• Describe how a substitution mutation would alter the gene coding for enzyme

  One base is replaced
• Explain how a substitution mutation may cause the synthesis of a faulty enzyme.

  The enzyme is shorter due to the presence of a stop codon.
• Use the metabolic pathway above to suggest

  i. why PKU results in a build-up of phenylalanine.

  Phenylalanine cannot be broken down
• why individuals with PKU can still produce melanin.

  They get tyrosine from their diet.
• State the term which describes a metabolic pathway in which simple molecules are built up into complex molecules.

  anabolic / synthesis
• Enzyme 1 is activated by the binding of magnesium ions.

  Suggest how the binding of these ions leads to an increase in enzyme activity.

  It lowers the activation energy.
• The conversion of glucose 6-phosphate to fructose 6-phosphate is a reversible reaction. Describe the circumstances under which this reaction would go in the opposite direction to that shown in the diagram.

  When there has been an increased concentration of fructose 6-phosphate.
• Explain why the addition of an inhibitor would slow down the rate of a reaction.

  Mutation or alteration of DNA.
• Explain why the time taken for the film to clear changed as trypsin concentration increased from 1% to 4%.

  There is more enzyme active sites to react with the substrate.
• Suggest why there was no change in the time taken to clear the

  film at trypsin concentration above 4%.

  Surface area of film is limiting the rate of reaction
• Explain why less agar jelly turned blue in this experiment than in the first experiment, which also used a 0.5 molar urea solution.

  The inhibitor blocked the active site on the enzyme.
• Suggest why some agar jelly turned blue in this experiment.

  Not all active sites were blocked
• The inhibitor used in the experiment was non-competitive.

  Describe how a non-competitive inhibitor works.

  It binds elsewhere on enzyme) / not to the active site and changes the shape of the active site.
• Suggest how the results would confirm that the inhibitor was non-competitive.

  The (final) alcohol concentration will not change
• A chromosome mutation in humans can result in the formation of the Philadelphia chromosome. The presence of this chromosome causes a form of leukaemia through the over-production of an enzyme.

  A drug has been used to successfully treat this form of leukaemia by blocking the active site of the enzyme.

  Name the type of enzyme inhibition shown by this drug.

  competitive
• White blood cell counts in humans normally range from 5000 to

  10,000 cells per μl of blood. The table shows the white blood cell counts

  from a patient with leukaemia before and after treatment with this

  drug.

  Explain how the results suggest that the type of leukaemia in this patient was a result of the presence of a Philadelphia chromosome.

  Drug was effective as white blood cell count reduced to normal.

  Drug works by inhibiting the enzyme produced by Philadelphia chromosome.
• Explain the role of the active site in enzyme-catalysed reactions.

  The substrate attaches to the active site (on the enzyme)

  This lowers the activation energy (required for the reaction to occur)

  Products are released as they have a low affinity to the active site.