BIOLOGICAL MOLECULES QUESTIONS WITH VERIFIED ANSWERS

What is digestion? - ANSWERSIt is the hydrolysis of larger insoluble molecules to soluble smaller molecules. Endocellulases and Exocellulases act at different points on a cellulose molecule - ANSWERS1. Active sites are different shapes; 2. So different enzyme-substrate complexes (are formed); OR So complementary to different parts of cellulose / substrate; What is a monomer? - ANSWERS(a monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made; What is isomer? - ANSWERSCompounds with the same chemical formula can have different arrangement of atoms. These molecules are called isomers. Describe the structure of a cellulose molecule and explain how cellulose is adapted for its function in cells. - ANSWERS1. made from β-glucose; 2. joined by condensation / removing molecule of water / glycosidic bond; 3. 1 : 4 link specified or described; 4. "flipping over" of alternate molecules; 5. hydrogen bonds linking chains / long straight chains; 6. cellulose makes cell walls strong / cellulose fibres are strong; 7. can resist turgor pressure / osmotic pressure / pulling forces; 8. bond difficult to break; 9. resists digestion / action of microorganisms / enzymes; (allow maximum of 4 marks for structural features) Describe how a peptide bond is formed between two amino acids to form a dipeptide - ANSWERS1. Condensation (reaction) / loss of water; Accept each marking point if shown clearly in diagram. 2. Between amine / NH2 and carboxyl / COOH; Accept between amino (group) and carboxylic / acid (group) The secondary structure of a polypeptide is produced by bonds between amino acids. Describe How. - ANSWERS1. Hydrogen bonds; Accept as a diagram Reject N - - - C / ionic / disulfide bridge / peptide bond 2. Between NH (group of one amino acid) and C=O (group); OR Forming β pleated sheets / α helix; Two proteins have the same number and type of amino acids but a different tertiary structure. Explain why. - ANSWERSThe arrangement of amino acid in each protien. Explain the difference in the structure of the starch molecule and the cellulose molecule shown in the diagram above. - ANSWERS1. Different sequence of amino acids OR Different primary structure; If candidate assumes proteins are the same, accept effect of different pH/ temperature 2. Forms ionic / hydrogen / disulfide bonds in different places; Explain how cellulose molecules are adapted for their function in plant cells - long answer - ANSWERS1. Insoluble; 2. Don't affect water potential; OR 3. Helical; Accept form spirals 4. Compact; OR 5. Large molecule; 6. Cannot leave cell. 2 (c) 1. Long and straight chains; 2. Become linked together by many hydrogen bonds to form fibrils; 3. Provide strength (to cell wall). Unsaturated vs Saturated - ANSWERSThey contain carbon-carbon bonds they are unable to accept more hydrogen bonds Starch (4) - ANSWERSHelical/spiral shape so compact Large and insoluble so osmotically inactive Branches so glucose is easily released for respiration Large molecule so can't leave the cell Glycogen - ANSWERS Human breast milk is produced and secreted by gland cells. These gland cells have adaptations that include many mitochondria and many Golgi vesicles. The milk contains a high concentration of protein. Explain the role of these cell adaptations in the production and secretion of breast milk. - ANSWERS1. (Many mitochondria) release energy / ATP for movement of vesicles / synthesis of protein / active transport; 2. (Many Golgi) vesicles transport protein / glycoprotein / milk to cell membrane / out of cel Describe the induced fit model of enzyme action. - ANSWERSActive site / enzyme not complementary; Active site changes (shape) / is flexible; (Change in enzyme allows) the substrate to fit / E-S complex to form; Active site becomes complementary / wraps around substrate = 2 marks The scientist used the same concentration of endocellulase and exocellulase in the mixtures. The rate of digestion of cellulose is greatest when both enzymes are present. Suggest why. - ANSWERS1. Endocellulase create more ends / increases surface area; 2. For exocellulase to act on / hydrolyse / digest; Lactulose is used to treat diarrhoea it is small soluble molecule. - ANSWERS1. (Lactulose) lowers the water potential of faeces / intestine / contents of the intestine; Accept Ψ for water potential 2. Water retained / enters (due to osmosis) and softens the faeces; Describe the biochemical test you would use to identify each of the following: - Reducing sugars - Non-reducing sugars - Starch - Proteins - Lipids (Spec 3.1, Biological Molecules) - ANSWERSReducing sugar 1. Heat with Benedicts reagent (blue); 2. Brick red (orange/green/yellow) precipitate formed as positive result; Non-reducing sugar 3. Boil with acid (break glycosidic bonds); 4. Heat with Benedicts reagent (blue); 5. Brick red (orange/green/yellow) precipitate formed as positive result; Starch 6. Add iodine / potassium iodide solution (orange/brown); 7. Blue/black colour as positive result; Proteins 8. Add Biuret reagent (blue); 9. Lilac/purple colour change as positive result; Lipids 10. Mix / crush / grind; with ethanol / alcohol; 11. Then add water; 12. Forms emulsion / goes white / cloudy as positive result;