Viruses are unique from all other life forms in that they can contain ONLY ONE FORM OF NUCLEIC ACID. Some viruses use RNA as their genetic material and other use DNA, but NEVER do they contain both. Further, this nucleic acid polymer may either exist as DOUBLE STRANDED (DS) DNA or RNA or as SINGLE STRANDED (SS) DNA or RNA. Each of these characteristics is a constant for a particular virus and is part of it description. The nucleic acid polymer may contain as few as 4 to 7 genes for very small viruses to 150 to 200 genes for very large viruses. In some viruses the nucleic acid exists in more that one molecule. Some viruses contain a few enzymes and some contain none, but no viruses contain the large numbers of enzymes found even in the smallest bacteriaAll viruses are covered with a PROTEIN COAT. This protein coat is mainly composed of a FEW TYPES of proteins of which there are many copies per virus; something like the individual threads in a shirt. These identical protein subunits are called CAPSOMERES and they are made so that they spontaneously come together (ASSEMBLE) in a PREDETERMINED way to produce the virus coat which is called the CAPSID.
If a virus has ONLY a protein capsid covering it, it is termed a NAKED CAPSID VIRUS or a NAKED VIRUS. However, some viruses pick up a lipid membrane from the host cell when it is released, that surrounds the capsid. The lipid membrane is called an ENVELOPE and such viruses are termed ENVELOPED VIRUSES. All virus contain one more important proteins type; this is ATTACHMENT PROTEIN or #docking proteins. The attachment protein is needed by the virus to ATTACH TO ITS TARGET CELL before it can enter that cell. Obviously this attachment protein must lie on the outer surface of the virus so that it is available to contact the appropriate RECEPTOR SITES on the target host cells. These attachment proteins are often called SPIKES because they can extend away from the cell so as to better be able to contact the host receptor (think of the viral AP & the host receptor site as being the pairs of a VELCRO SYSTEM). In addition, virus may contain small quantities of carbohydrate (glycoprotein).
If a virus has ONLY a protein capsid covering it, it is termed a NAKED CAPSID VIRUS or a NAKED VIRUS. However, some viruses pick up a lipid membrane from the host cell when it is released, that surrounds the capsid. The lipid membrane is called an ENVELOPE and such viruses are termed ENVELOPED VIRUSES. All virus contain one more important proteins type; this is ATTACHMENT PROTEIN or #docking proteins. The attachment protein is needed by the virus to ATTACH TO ITS TARGET CELL before it can enter that cell. Obviously this attachment protein must lie on the outer surface of the virus so that it is available to contact the appropriate RECEPTOR SITES on the target host cells. These attachment proteins are often called SPIKES because they can extend away from the cell so as to better be able to contact the host receptor (think of the viral AP & the host receptor site as being the pairs of a VELCRO SYSTEM). In addition, virus may contain small quantities of carbohydrate (glycoprotein).
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