Biology 9700 · AS & A Level · Genetic technology applied to medicine

Genetic technology applied to medicine — practice question

The bacterium Treponema pallidum is the cause of syphilis, a sexually transmitted infectious disease. If it is not treated, the disease may be fatal, although early diagnosis can result in successful treatment. A key problem when diagnosing it in the early stages is distinguishing T. pallidum from other Treponema species that live in humans. These other treponemes do not cause harm. A mouse was injected with some cells of T. pallidum.
(a)[4]

Outline the steps that would then be needed to make a clone of hybridoma cells that secretes an antibody against this bacterium.

(b)[3]

Suggest how H9-1 is used in the diagnosis of syphilis, using a sample taken from a sore and placed on a microscope slide.

(c)[2]

Before H9-1 was developed, two tests were used to look for T. pallidum: dark-field microscopy, where treponemes could be seen moving against a dark background, and testing for anti-treponemal antibodies in blood plasma. Suggest why, at the early stage of an infection, the presence of T. pallidum might escape detection by either of these tests.

(d(i))[3]

Using Table 2.1, compare how accurately the different tests diagnose the presence of T. pallidum.

(d(ii))[1]

Suggest why blood testing for anti-treponemal antibodies gave two positive results in patients who were later shown not to have the infection.

(e)[2]

Describe briefly one use of a monoclonal antibody in the treatment of disease.

Worked solution & mark scheme

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