State the source, substrate, products and optimal pH condition for lipase in the human digestive system.

Outline the use of named enzymes in gene transfer using plasmids.

Explain the effect of changes of pH, substrate concentration and temperature on enzyme activity.

eg source: pancreas;
substrate: triglycerides / lipids / fats / oils;
product: glycerol and (three) fatty acids; (both needed)
optimal pH: 8; (accept answers in the range of 7 to 8)
Accept other correct examples.

a. plasmids are removed/obtained from bacteria;
b. endonuclease/restriction enzymes cut the plasmids at target sequences;
c. DNA fragments of other organism are cut with the same restriction enzymes;
d. in both DNA and plasmid, complementary sticky ends/staggered cut are produced;
e. DNA segment added to the opened plasmid;
f. spliced together by ligase;
g. reverse transcriptase makes DNA copies of mRNA / DNA polymerase to increase the amount of DNA;
h. recombinant plasmids inserted into new/host cells;
i. cultured/cloned to produce the new genes/more genetically modified cells;
Award [3 max] if no specific enzyme names are given.
Do not accept the word “enzyme” on its own.

pH:
a. enzymes have an optimal pH/work best at a given pH;
b. activity increases as pH gets closer to optimal pH;
c. extreme pH denatures enzymes;
d. by breaking bonds / changing enzyme shape/structure / active site shape/structure;

substrate:
e. as substrate concentration increases, activity increases;
f. as substrate concentration increases, the collisions between substrate and enzyme increase;
g. up to a maximal level of action / reaching a plateau;
h. all active sites are saturated/occupied;

temperature:
i. enzymes have an optimal temperature (where they work most effectively);
j. activity increases as it gets closer to optimal temperature;
k. high temperatures stop enzyme activity due to irreversible changes in structure / denaturation;
l. by breaking bonds / changing enzyme shape/structure / active site shape/structure;
Award any of the above points in an annotated graph.
Award up to [8] if all three addressed and [6 max] if only two addressed.

Clear answers were given by most of the students that had the knowledge.

Some students got confused with other biological techniques, making reference to PCR for example, apart from explaining correctly some steps in gene transfer. There was often no mention of reverse transcriptase.

Most of the students scored marks for this answer, some of them confused the graphs of temperature and pH with the one of substrate concentration, consequently their explanations were incorrect. A number of students incorrectly wrote that the enzyme denatures once it reaches its optimal temperature or pH, so marks were not awarded.