Biology 9700 · AS & A Level · Infectious diseases

Infectious diseases — practice question

Baculovirus is a virus that destroys some insect pests of major crops. Once the virus leaves the insect body, it is enclosed in tough, protective particles called polyhedrons. Polyhedrin, a protein molecule, makes up most of the polyhedron. Polyhedrons may be sprayed onto plants as a bioinsecticide. Feeding insect larvae eat them, and when they reach the insect gut they dissolve and release the virus.
(a)[2]

Explain why the phrase infectious disease can be used to describe the effect of baculovirus on insects.

(b)[2]

Suggest and explain the conditions inside the insect gut that could lead to polyhedrons breaking down.

(c)[4]

A polyhedrin molecule consists of three identical polypeptides. Each polypeptide contains 245 amino acids. The first 10 amino acids of the polypeptide are shown in Fig. 3.1. Using Fig. 3.1 and Fig. 3.2, describe the structure of a polyhedrin molecule.

(d)[3]

The DNA nucleotide sequence of the gene in baculovirus that codes for the polyhedrin polypeptide has been identified. Explain why the amino acid sequence of the polypeptide cannot be used to deduce the sequence of nucleotides in the gene that codes for the polyhedrin polypeptide.

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This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Baculovirus is infectious and transmissible from one insect to another.” …

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