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==Structure of Viruses==
The fundamental component of a virion is the nucleoprotein core that contains the genetic ability to infect host cells and replicate inside them. The genome of viruses able to infect vertebrates is enclosed by a capsid and is haploid in all cases except retroviruses in which they are diploid. The nuclear material and the capsid are called the nucleocapsid. Capsids are made up of multiples of one or more types of protein subunits and it is this orderly arrangement of types of protein that creates a symmetrical structure.
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In many virus species the nucleocapsid is covered by an envelope composed of a lipid bilayer and glycoproteins. This envelope is acquired when the nucleocapsid buds through the lipid bilayer of the host cell. In some viruses this envelope is acquired from the endoplasmic reticulum or the golgi apparatus. This represents an important element of virus structure in that the proteins encoded by the viral nucleic acid are integrated into the glycoprotein envelope in the appropriate manner to ensure that the virus has the ability to bind to receptors on host cells. In most enveloped viruses the virus must remain intact to ensure that the virus is infective.
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Viruses also have a layer of protein called the "matrix" which is between the nucleocapsid and the envelope. The matrix layer provides the overall virus structure with increased rigidity.
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[[Image:Virus structure.jpg|thumb|right|150px|Virus Structure - B. Catchpole, RVC 2008]]
[[Image:Virus structure.jpg|thumb|right|150px|Virus Structure - B. Catchpole, RVC 2008]]
Outside the host cell, viruses exist as particles known as virions, consisting essentially of the virus genome, packaged in a 'capsid,' and a lipid component, which contains proteins that aid entry into the host cell. Viruses can be classified as either:
Outside the host cell, viruses exist as particles known as virions, consisting essentially of the virus genome, packaged in a 'capsid,' and a lipid component, which contains proteins that aid entry into the host cell. Viruses can be classified as either:
'''Membranes''':
'''Membranes''':
*Most viruses have a lipid membrane. If present at the surface, the membrane is known as the 'envelope'. Several viruses keep the lipid membrane within themselves
*Most viruses have a lipid membrane. If present at the surface, the membrane is known as the 'envelope'. Several viruses keep the lipid membrane within themselves
**Often associated with proteins such as glycoproteins- these often aid the fusion process[[Category:Viruses]]
**Often associated with proteins such as glycoproteins- these often aid the fusion process
[[Category:Viruses]]
[[Category:To_Do_-_Clinical/Viruses]]
[[Category:To_Do_-_Clinical/Viruses]]