CAPSID AND ENVELOPE

CAPSID AND ENVELOPE - used for identification, and they...

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CAPSID AND ENVELOPE The nucleic acid is surrounded by a protein coat called the capsid. The capsid composed of  protein subunits called capsomeres. The structure of these viral proteins is determined by genes  of the virus. The arrangement of the capsomeres is characteristic of the virus. With the electron  microscope, individual capsomeres may be visible.   Some viruses have an additional outer covering called an envelope. This is composed of lipids,  proteins, and carbohydrates. If a virus has this covering, it acquired it as it was released from an  animal host cell. The envelope is basically plasma membrane of the host cell, but the proteins it  contains are viral proteins.   In some viruses, the envelope is covered by projections called spikes. These project from the  surface of the envelope and may be used by the virus to attach to host cells. The spikes can be 
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Unformatted text preview: used for identification, and they also enhance the pathogenicity of some viruses. For example, the virus that causes influenza has spikes that bind to red blood cells and cause them to clump together (hemagglutination). Nonenveloped viruses do not have the envelope. In these the capsid provides the protection for the nucleic acid and attaches to host cells. Whether the outer covering of a virus is an envelope or the capsid, it is this outer covering to which the immune system of the host responds by producing antibodies, which should be capable of binding to and inactivating the virus. Some viruses slip past this defense by frequently changing the characteristics of their outer covering to that the antibodies not longer recognize it. Influenzavirus is outstanding at this trick, and this is why flu shots have to change every year....
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CAPSID AND ENVELOPE - used for identification, and they...

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