2.2. Carbohydrates and lipids
A subsection of Biology, 9700, through 2. Biological molecules
Listing 10 of 368 questions
Triglycerides and phospholipids are types of lipid. shows the structure of one type of phospholipid known as phosphatidylcholine. F1 and F2 are fatty acid residues. CH3 CH2 CH2 H2C CH C O O CH3 H3C N+ CH2 O P O O– O O F2 C O F1 choline Phospholipase is an enzyme that can break down phospholipids. This enzyme is found in the venom of some insects, such as bees. Bee venom can destroy red blood cells, a condition known as haemolysis. Suggest how bee venom destroys red blood cells. Compare, stating similarities and differences, the structure of the phosphatidylcholine shown in with the structure of a triglyceride molecule. similarities differences Name and describe the cell structure in which the synthesis of triglycerides and other lipids takes place.
9700_w17_qp_22
THEORY
2017
Paper 2, Variant 2
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shows the molecular structure of a triglyceride molecule. C H H O O H H H H H H H H H H C C C C C C H C H O O H H H H H H H H H H C C C C C C H C H O O H H H H H H H H H H H C C C C C C H Draw a circle around an ester bond shown in . Name the type of reaction used to produce a triglyceride from its components. State the number of water molecules produced during this reaction. type of reaction number of water molecules produced Lipases are enzymes that digest triglycerides in the lumen of the human intestine. These enzymes are released by exocytosis from intestinal epithelial cells. Underline all the terms from the list that are used to describe these lipases. macromolecule extracellular enzyme fibrous protein polysaccharide Scientists have found that treating milk with lipase can improve its taste. The scientists carried out an experiment to determine the effect of lipase activity on the triglycerides found in milk. • Lipase was immobilised in alginate beads. • The pH of a known volume of milk was adjusted to pH 8 by adding an alkali. • The beads were then mixed with this milk in a beaker. • The pH of the reaction mixture was recorded over a period of 24 hours. The results are shown in . 6.0 time / h 6.2 6.4 6.6 6.8 7.0 7.2 pH of reaction mixture 7.4 7.6 7.8 8.0 shows that the pH decreases steeply and then, after 18 hours, remains constant. Calculate the time taken for the pH to decrease from pH 6.6 to pH 6.3. time taken = h Explain the results shown in . The scientists repeated the experiment using a higher concentration of lipase. All other variables remained constant. Predict how an increase in the concentration of the lipase would affect the results of the experiment.
9700_w20_qp_21
THEORY
2020
Paper 2, Variant 1
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Phosphatidate phosphatase (PAP) enzymes have an important role in lipid metabolism. The reaction catalysed by PAP is shown in . phosphatidate + H2O PAP diglyceride + inorganic phosphate (PExperiments were carried out to investigate the activity of PAP extracted from the cotyledons (seed leaves) of bitter gourd, Momordica charantia. There are two types of PAP enzymes: • PAP1 enzymes need magnesium ions (Mg2+) in the active site to function • PAP2 enzymes do not need Mg2+. The effect of different concentrations of Mg2+ on the activity of PAP extracted from M. charantia was investigated. The results are shown in . 0.0 0.0 10.0 20.0 30.0 40.0 0.5 1.0 1.5 concentration of Mg2+ / mmol dm–3 PAP activity / arbitrary units 2.0 2.5 3.0 Explain, with reference to , whether the PAP extracted from M. charantia is a PAP1 enzyme or a PAP2 enzyme. shows the effect of increasing phosphatidate concentration on the activity of PAP extracted from M. charantia. phosphatidate concentration / μmol dm–3 PAP activity / arbitrary units With reference to , describe and explain the effect of increasing phosphatidate concentration on the activity of PAP. The diglycerides formed as a result of the action of PAP can be used to synthesise triglycerides and membrane phospholipids. Explain how the structure of a triglyceride is suited to its function as an energy storage molecule. Explain why phospholipids are able to form a bilayer in cell membranes.
9700_m20_qp_22
THEORY
2020
Paper 2, Variant 2
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