A virus particle, also known as a virion, is essentially a nucleic acid ( HYPERLINK "http://biology.about.com/od/geneticsglossary/g/DNA.htm"DNA or RNA) enclosed in a protein shell or coat. Viruses are extremely small, approximately 15 - 25 nanometers in diameter. Viruses: Genetic Material
Viruses may have double-stranded DNA, double-stranded RNA, single-stranded DNA or single-stranded RNA. The type of genetic material found in a particular virus depends on the nature and function of the specific virus. The genetic material is not typically exposed but covered by a protein coat . The viral genome can consist of a very small number of genes or up to hundreds of genes depending on the type of virus. Note that the genome is typically organized as a long molecule that is usually straight or circular. Viruses: Capsids
The protein coat that envelopes viral genetic material is known as a capsid. A capsid is composed of protein subunits called capsomeres. Capsids can have several shapes: polyhedral, rod or complex. Capsids function to protect the viral genetic material from damage. In addition to the protein coat, some viruses have specialized structures. For example, the flu virus has a membrane-like envelope around its capsid. The envelope has both host cell and viral components and assists the virus in infecting its host. Capsid additions are also found in bacteriophages . For example, bacteriophages can have a protein "tail" attached to the capsid that is used to infect host bacteria .
Transmission of viruses
Viruses can be transmitted by travelling within a fluid, such as mucus droplets from a sneeze. Once they have entered a living host they begin the process of replication. This replication process always follows a particular pattern. Attachment Virus binds to a specific receptor on the host cell surface. Penetration The viral nucleic acid enters the cell.
Synthesis of new components. Viral nucleic acid takes over control of the...
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