Scientists have long sought to uncover the structure and function of viruses. Viruses are unique -- they have been classified as both living and nonliving at various points in the history of biology. What makes them so interesting? Let's look at the structure of viruses.
Structure
A virus particle, also known as a virion, is essentially a nucleic acid (DNA or RNA) enclosed in a protein shell or coat. Viruses are extremely small, approximately 15 - 25 nanometers in diameter.
Structure
A virus particle, also known as a virion, is essentially a nucleic acid (DNA or RNA) enclosed in a protein shell or coat. Viruses are extremely small, approximately 15 - 25 nanometers in diameter.
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Genetic Material
Viruses may have double-stranded DNA, double-stranded RNA, single-stranded DNA or single-stranded RNA. In different viruses, which of the four is the "genetic material," depends on the nature and function of the specific virus.
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.
Protein Coat
The protein coat that envelopes the genetic material is known as a capsid. It can have several shapes: polyhedral, rod or "complex." The protein subunits of the capsid are called capsomeres.
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Tobacco Mosaic virus and T4 Bacteriophage images copyrightDennis Kunkel. | ||
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.
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Image courtesy of Linda M. Stannard, University of Cape Town. | |
Capsid additions are also found in bacteriophages. For example, bacteriophages can have a protein "tail" attached to the capsid that is used to infect the host bacteria.
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