EXAM QUESTIONS

• DESCRIBE HOW MONOMERS JOIN TO FORM THE PRIMARY STRUCTURE OF A PROTEIN

  A condensation reaction forms between amino acids forming peptide bonds. This creates a specific sequence of amino acids.
• MANY PROTEINS ARE ENZYMES.

  IN 1894, A SCIENTIST SUGGESTED THE LOCK AND KEY MODEL OF ENZYME ACTION.

  FIGURE 5 SHOWS THE LOCK AND KEY MODEL.

  DESCRIBE ONE SIMILARITY AND ONE DIFFERENCE BETWEEN THE INDUCED-FT MODEL OF ENZYME ACTION AND THE LOCK AND KEY MODEL OF ENZYME ACTION.

  SIMILARITIES:

  • substrate fits/binds to active site.
  • enzyme-substrate complex formed

  DIFFERENCES:

  • the active site changes shape, but doesn’t change in lock and key.
  • Initially, the active site isn’t complementary to substrate with induced fit, but it’s complementary in lock and key.

  
• STATE HOW ENZYMES HELP REACTIONS TO PROCEED QUICKLY AT LOWER TEMPERATURES (DON’T WRITE ABOUT ACTIVE SITES)

  there is a lower activation energy which is needed to start a reaction.
• Figure 6

  Increased maltase concentration

  
• NAME THE MAIN POLYMER THAT FORMS THE FOLLOWING CELL WALLS:

  • PLANT CELL WALL:
  • FUNGAL CELL WALL:

  plant cell wall: cellulose

  fungal cell wall: chitin
• THIS AP HAS A SECONDARY STRUCTURE IN A HELICAL SHAPE.

  WHICH TYPE OF BOND MAINTAINS THE HELICAL STRUCTURE OF THE POLYPEPTIDE?

  Hydrogen
• TWO ENZYMES, P AND Q, ADE PROTEINS WITH QUATERNARY STRUCTURE WHICH CATALYSE THE SAME REACTION, BUT THEY HAVE DIFFERENT AMINO ACID SEQUENCES.

  DEFINE THE QUATERNARY STRUCTURE OF A PROTEIN.

  more than one polypeptide.
• EXPLAIN HOW TO TWO ENZYMES WITH DIFFERENT AMINO ACID SEQUENCES CAN CATALYSE THE SAME REACTION

  1. Both active sites have similar tertiary structures.

  OR

  1. Both active sites have identical amino acid sequences.

  2. So form enzyme-substrate complexes with the same substrate,
• SCIENTISTS INVESTIGATED THE EFFECT OF PH 8.4 AND PH 7.5 ON THE ACTIVITY IF ENZYMES P AND Q

  FIGURE 8 SHOWS THEIR RESULTS.

  DESCRIBE WHAT THE SCIENTISTS SHOULD PLACE IN THE CONTROL TUBES IN THIS INVESTIGATION.

  1. The same volume of each buffer/pH solution.

  2. same concentration/mass of substrate at the start.

  3. same concentration/mass of denatured enzyme.

  
• GIVE THREE CONCLUSIONS YOU CAN MAKE FROM FIGURE 8 (3 marks)

  1. Both P and Q are active at pH 8.4.
  2. P is most active at both pHs

  2. Q is less active than P at both pHs.

  2. P is not affected by pH (change)

  2. Q is affected by pH (change)

  3. Q is denatured/not active at pH 7.5

  3. Q is less active than the control at pH 7.5

  4. Reaction occurs without enzymes

  4. Reaction occurs in the control

  5. All reactions reach the same end point

  5. Substrate isn’t used up

  
• Polysaccharides

  Both starch and cellulose are polysaccharides
• Glucose polymers

  Both starch and cellulose are glucose polymers
• Both starch and cellulose are made of glucose monomers
• Both starch and cellulose contain glycosidic bonds between monomers
• Both starch and cellulose contain carbon, hydrogen, and oxygen
• Starch

  • Has alpha glucose
  • Is helical
  • Is branched
• Cellulose

  • Has beta glucose
  • Is straight
  • Is unbranched
  • Has micro fibrils
• Starch has 1-6 glycosidic bonds and cellulose doesn't
• Starch

  Contains two types of molecule: amylose and amylopectin
• Cellulose

  Contains one type of molecule
• DESCRIBE THE CHEMICAL REACTIONS INVOLVED IN THE COVERSION OF POLYMERS TO MONOMERS AND MONOMERS TO POLYMERS. GIVE TWO NAMED EXAMPLES OF POLYMERS AND THEIR ASSOCIATED MONOMERS.

  1. A condensation reaction joins monomers together and forms a chemical bond and releases water.
  2. a hydrolysis reaction breaks a chemical bond between monomers and uses water.
  3. EXAMPLE: amino acid and polypeptide, enzyme antibody OR nucleotide and polynucleotide, DNA or RNA OR alpha (beta) glucose and starch/glycogen (cellulose)
  4. another example
  5. correct bond with a named polymer.
• WHAT IS A MONOMER?

  A smaller, repeating unit from which larger polymers are made.
• TABLE

  B, D, C, B

  
• Raffinose is a trisaccharide of three monosaccharides: galactose, glucose and fructose. The chemical formulae of these monosaccharides are:

  • galactose = C6H12O6

  • glucose = C6H12O6

  • fructose = C6H12O6

  Give the number of carbon atoms, hydrogen atoms and oxygen atoms in a molecule of raffinose.

  NO. OF CARBON ATOMS = 18

  NO. OF HYDROGEN ATOMS = 32

  NO. OF OXYGEN ATOMS = 16
• A BIOCHEMICAL TEST FOR REDUCING SUGAR PRODUCES A NEGATIVE RESULT WITH RAFFINOSE SOLUTION.

  DESCRIBE A BIOCHEMICAL TEST TO SHOW THAT RAFFINOSE SOLUTION CONTAINS A NON-REDUCING SUGAR.

  1. heat with acid and neutralise.
  2. heat with Benedict’s solution.
  3. result should be brick red precipitate.
• A (IMAGE) STUDENT CARRIED OUT THE BENEDICTS TEST. SUGGEST A METHOD, OTHER THAN USING A COLORIMETER, THAT THIS STUDENT COULD USE TO MEASURE THE QUANTITY OF REDUCING SUGAR IN A SOLUTION

  1. Filter and dry
  2. find mass/weight

  
• (IMAGE) EXPLAIN THE RESULTS FOR BEAKERS A AND B IN THE TABLE

  A = glucose

  B = maltose

  because more sugar/precipitate after hydrolysis/maltase action

  
• USE OF A COLORIMETER IN THIS INVESTIGATION WOULD IMPROVE THE REPEATABILITY OF THE STUDENTS RESULTS. GIVE ONE REASON WHY.

  1. Quantitive OR colour change is subjective
  2. standardises the method
• LACTULOSE IS A DISACCHARIDE FORMED FROM ONE MOLECULE OF GALACTOSE AND ONE MOLECULES OF FRUCTOSE.

  OTHER THAN BOTH BEING DISACCHARIDES, GIVE ONE SIMILARITY AND ONE DIFFERENCE BETWEEN THE STRUCTURES OF LACTULOSE AND LACTOSE.

  SIMILARITY:

  1. Both contain galactose/ a glycosidic bond

  DIFFERENCE:

  2. Lactulose contains fructose, whereas lactose contains glucose.
• GLYCOGEN AND CELLULOSE ARE BOTH CARBOHYDRATES.

  DESCRIBE TWO DIFFERENCES BETWEEN THE STRUCTURE OF A CELLULOSE MOLECULE AND A GLYCOGEN MOLECULE.

  1. Cellulose is made up of beta glucose monomers and glycogen is made up of alpha glucose monomers.
  2. cellulose molecule has straight chain and glycogen is coiled
  3. glycogen has 1,4- and 1,6- glycosidic bonds and cellulose has only 1,4- glycosidic bonds.
• STARCH IS A CARBOHYDRATE OFTEN STORED IN PLANT CELLS. DESCRIBE AND EXPLAIN TWO FEATURES OF STARCH THAT MAKE IT A GOOD STORAGE MOLECULE.

  1. Insoluble in water doesn’t affect water potential.
  2. branched/coiled/alpha helix so makes the molecule compact Which allows many to fit into a small area.
  3. Polymer of alpha glucose so provides glucose for respiration
  4. branched for fast enzyme action
  5. large molecule so can’t cross the cell membrane
• WHAT TEST WOULD BE USED TO SHOW THE PRESENCE OF STARCH?

  iodine/potassium iodide test
• DESCRIBE THE STRUCTURE OF GLYCOGEN

  1. polysaccharide of alpha glucose
  2. joined by glycosidic bonds
• DURING EARLY PREGNANCY, THE GLYCOGEN IN THE CELLS LINING THE UTERUS IS AN IMPORTANT ENERGY SOURCE FOR THE EMBRYO. SUGGEST HOW GLYCOGEN ACTS AS A SOURCE OF ENERGY. DO NOT INCLUDE TRANSPORT ACROSS MEMBRANES IN YOUR ANSWER.

  1. hydrolysed into glucose
  2. glucose used in respiration
• NAME THE MONOMERS FROM WHICH A MALTOSE MOLECULE IS MADE

  glucose and glucose
• NAME THE TYPE OF CHEMICAL BOND THAT JOINS THE TWO MONOMERS TO FORM MALTOSE

  (Alpha 1,4) glycosidic
• (IMAGE)

  HEADINGS: mol dm-3 AND volume of water/ cm3

  CONCENTRATION: 0.2

  
• (IMAGE) EXPLAIN HOW YOU WOULD USE TEH GRAPH TO DETERMINE THE MALTOSE CONCENTRATION WITH A LIGHT ABSORBANCE OF 0.45 ARBITRARY UNITS.

  line of best fit drawn, read off value at 0.45

  
• (IMAGE) EXPLAIN THE DIFFERENCE IN THE STRUCTURE OF THE STARCH MOLECULE AND THE CELLULOSE MOLECULE SHOWN IN THE DIAGRAM.

  1. Starch formed from an alpha glucose but cellulose formed from beta glucose
  2. position of hydrogen and hydroxyl groups on carbon atom 1 inverted.

  
• STARCH MOLECULES AND CELLULOSE MOLECULES HAVE DIFFERENT FUNCTIONS IN PLANT CELLS. EACH MOLECULE IS ADAPTED FOR ITS ACTION. EXPLAIN ONE WAY IN WHICH STARCH MOLECULES ARE ADAPTED FOR THEIR FUNCTION IN PLANT CELLS.

  1. insoluble so don’t affect water potential
  2. helical so compact
  3. large molecule so can’t leave cell