A virus is a tiny particle (between about 20 and 800 nm in size, 1 nm = 1 × 10–9m) made from a protein coat (called a capsid) containing some genetic material such as DNA. A virus infects a host cell by injecting its genetic material, which hijacks the cell, forces it to replicate the viral DNA and directs it to produce the protein components to build new capsids. Viruses that infect bacteria are known as bacteriophages (Figure 1).
While the mechanism of viral infection is reasonably well understood, less is known about how viral particles assemble. The process starts after viral genetic information enters the cell and ‘deceives’ it into producing everything necessary for the assembly of the virus. For the majority of bacteriophages the assembly begins with the formation of a procapsid around a portal protein. The portal protein contains a specific ‘doorway’ for DNA to pass through, formed by a circular assembly of 12 identical subunits (Figure 2). Another viral protein called terminase recognises the viral DNA and its interaction with the capsid leads to the formation of an active molecular motor (Figure 3). This motor uses energy from the conversion of ATP to ADP (see CHEMISTRY REVIEW, Vol. 19, No. 1, p. 7) to transfer the DNA into the capsid at a speed of about 300 nm per second. When the DNA is completely packed into the new virus, several more protein components are attached to the capsid, leading to the formation of a mature viral particle.
Your organisation does not have access to this article.
Sign up today to give your students the edge they need to achieve their best grades with subject expertise
Subscribe
