Biology 9700 · AS & A Level · Infectious diseases

Infectious diseases — practice question

The fig tree, Ficus carica, and the papaya tree, Carica papaya, both yield a milky fluid called latex. This latex is discharged when plant tissue is damaged and is believed to provide defence against attack by herbivorous insects or parasitic worms. Latex is a complicated blend of substances, and its precise makeup varies with plant species. Enzymes that hydrolyse proteins, called cysteine proteases, are often present in latex. Ficin, found in F. carica, and papain, found in C. papaya, are both cysteine protease enzymes. These enzymes have been removed and purified for commercial use.
(a(i))[3]

Using Fig. 5.1 as a reference, describe how the activity of papain differs from that of ficin over the range $20\,^{\circ}\text{C}$ to $80\,^{\circ}\text{C}$.

(a(ii))[1]

Ficin and papain have been found to work effectively in the digestion of parasitic nematodes (roundworms). Using Fig. 5.1, explain which enzyme you would choose for an oral medicine to treat human intestinal parasitic nematodes.

(b)[1]

One commercial application of ficin is making Fab fragments (antigen binding regions) of mouse IgG antibodies for immunological studies. The method uses immobilised ficin to cut the antibodies in the hinge region. Suggest one practical benefit of using immobilised ficin in this process instead of ficin in free solution.

(c(i))[1]

Streptococcus pyogenes is a bacterium that can cause a variety of diseases in humans. S. pyogenes produces streptopain, a cysteine protease that hydrolyses structural proteins in human connective tissue. Streptopain is released outside the cell. State the term used for an enzyme that is made by a cell and then secreted to the outside, where it acts.

(c(ii))[1]

Suggest one example of a structural protein found in connective tissue that streptopain can hydrolyse.

Worked solution & mark scheme

This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: Papain’s optimum temperature is higher than ficin’s

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