A-LevelBiologyBiological molecules9700/22 · May/June 2017 · Q211 Marks

Lipase is an enzyme with many commercial uses. Some species of bacteria are of great interest as they produce large quantities of lipase.

(a)Complete Fig. 2.1 to show the hydrolysis of triglyceride by lipase. triglyceride + `_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _` lipase `_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _` [Figure 2.1][2]
(b)Researchers carried out investigations into lipase extracted from a bacterium found in hot springs. To measure the activity of the bacterial lipase during their investigations, the researchers used a method based on the biological test for triglycerides. Outline a biological test that could be carried out to show the presence of triglyceride in a liquid mixture and describe the positive result for this test.[3]
(c)The researchers investigated the effect of pH values between pH2.0 and pH 10.5 on the activity of bacterial lipase in hydrolysing triglyceride at a temperature of 37 °C. The results are shown in Fig. 2.2. [Figure 2.2] With reference to Fig. 2.2, describe the effect of pH on the activity of bacterial lipase.[4]
(d)(i)A separate investigation into the effect of pH on the same bacterial lipase compared the enzyme free in solution with the enzyme immobilised by physical attachment to a stable polymer. At a temperature of 37°C, the optimum pH of the enzyme free in solution was the same as that shown in Fig. 2.2. The optimum pH of the immobilised enzyme was measured as pH4. Suggest one reason to explain why the enzyme free in solution has a different optimum pH compared to the immobilised enzyme.[1]
(d)(ii)Suggest one advantage of immobilising the extracted lipase for commercial use.[1]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.

[1] addition of water shown; A H₂O
[1] fatty acid(s) and glycerol ;
[1] ref. to mixing with / dissolving in / adding / adding to, alcohol / ethanol ; R if incorrect substance added to alcohol, e.g. fatty acids, then allow ecf
[1] then, add/add to, water;
[1] positive result emulsion; I on top / throughout A milky (layer) / cloudy (suspension) / opaque / white droplets R precipitate
[1] increase (pH2) to pH7, decrease from pH7 (to pH10.5); A trend described as increase then decrease
[1] optimum / peak / maximum activity / 99% / 100% (relative) activity, at pH7 ;
[1] steep(er) decrease from, pH7 / optimum, (to pH10.5); in context of steepness of increase from pH2–7
[1] detail either side of optimum (pH2–7 or pH7–10.5); pH2-7 less steep (increase) pH5–pH7 / little difference between pH5 and 6/ steepest increase between pH2–4 or pH 7–10.5 steeper decrease between pH 7 and 7.5 / less steep decrease between pH 7.5 and 10.5
[1] activity, pH2–7 / below 7, higher than activity, after pH8; A in, alkaline / basic, pH / conditions A enzyme works better in acidic and neutral conditions ora A enzyme works better in acidic than, alkaline / basic, conditions ora
[1] enzyme active throughout the pH range;
[1] data/manipulated data, (to support above mps); needs comparison values, pH and, percentage activity/%
[1] ref. to partial denaturation at higher pH ; A starts to denature
[1] (immobilised) support material/AW, affects enzyme action ;
[1] support material is charged ;
[1] idea that free has greater exposure to hydrogen ions or immobilised has protection from hydrogen ions ;
[1] idea that immobilised has changed ability to catalyse ;
[1] immobilised has (slightly) altered active site ; R ref. to denaturation I changes to tertiary structure
[1] support material causes change to, external/substrate, solution;
[1] can be re-used ;
[1] can be easily recovered;
[1] easier downstream processing;
[1] product, not/less, contaminated;
[1] longer shelf life of enzyme ;
[1] more stable;
[1] can use higher temperatures (owing to protective matrix);
[1] more productive ;
[1] less time-consuming ;
[R] cost alone is not enough