Scientists have produced structures known as virosomes, which are used in certain vaccines. Virosomes do not cause disease. Fig. 4.1 is a diagram of a section through a virosome used in some vaccinations to protect against the virus which causes influenza. [Figure 4.1]

1. (a)(i)State the differences between the structure of a virosome and a virus.[2]
2. (a)(ii)Explain how the structure of the virosome shown in Fig. 4.1 suggests that the central area of the virosome is aqueous.[2]
3. (b)The glycoproteins haemagglutinin and neuraminidase are found in the influenza virus and in the virosomes used in a vaccine against the influenza virus. Haemagglutinin binds to a receptor in the cell surface membrane of phagocytes. Suggest why haemagglutinin is present in virosomes used in the vaccine for influenza.[2]
4. (c)Different strains of the influenza virus have formed as a result of mutations. Each strain of the virus contains the enzyme neuraminidase. Neuraminidase helps the virus to leave host cells after the virus has replicated. In each strain of the influenza virus, the primary structure of the active site of the neuraminidase enzyme remains unchanged. Suggest why the primary structure of the active site of neuraminidase remains unchanged in each strain of the influenza virus.[2]

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