Viruses (AQA A Level Biology): Revision Note
Exam code: 7402
The structure of viruses
Viruses are non-living because they:
are non-cellular
cannot reproduce independently (they require a host)
do not grow or respond to stimuli
do not carry out protein synthesis (they use the protein-building machinery in host cells)
They have no metabolic activity
All viruses are parasitic
They are much smaller than prokaryotic and eukaryotic cells
Structurally they have:
Genetic material: either DNA or RNA, and can be single or double-stranded
A capsid: a protein coat surrounding genetic material and containing attachment proteins
Attachment proteins: these bind to receptors on host cells during invasion

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