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Viruses are composed of a central core of nucleic acid surrounded by a protein coat (Capsid) which is made up of capsomeres.

Most of the viruses exhibit characteristic symmetry:

  1. Icosahedral: In case of spherical viruses
  2. Helical: In case of rod-shaped viruses
  3. Complex: In case of miscellaneous group

The nucleic acid core along with the capsid forms the Nucleocapsid. In some viruses, the nucleocapsid is covered by an outer membrane like structure called the envelope which is made up of lipids and proteins. It is 100-150A thick and is derived from the host plasma membrane. The viruses covered by envelop are Influenza virus, Mumps virus, Herpes virus and Rous Sarcoma virus.

Nucleic Acids:

The viral genome contains all the genetic information and is composed of nucleic acid. However, the virus contain either DNA or RNA but neither both which is in contrast to all cellular forms of life which contains both types of nucleic acids. On this basis, two classes of viruses were recognized: DNA Viruses and RNA Viruses

Other Chemical Components:

  1. Carbohydrates: All viruses contain carbohydrates since the nucleic acid itself contains deoxyribose or ribose. Enveloped viruses such as Influenza virus have spikes made up of glycoprotein on its envelop
  2. Protein: Protein is the major chemical component of the virion The capsid is made up of proteins.
  3. Lipid: Phospholipid is the predominant lipid substance found in the viral envelope. A variety of lipid compounds such as glycolipids, phospholipids, fatty acids and cholesterol have been found in viruses. 
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