Viruses
A fully infective virus is called a viron. The genomes of viruses are much smaller than those found in prokaryotic and eukaryotic cells and in most viruses the nucleic acid is present in a single molecule. The genomes of viruses can be either single or double-stranded and viruses can contain either RNA or DNA. Due to this viruses can be catagorised into three main groups based on their nucleic acid composition; DNA viruses, RNA viruses and viruses which utilise both DNA and RNA for replication.
