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Viruses are acellular entities and have no complete cellular structure.  Structurally, they are made up of:

1. Envelope:

  1. It is the outer thin loose covering present in some viruses.
    Eg.  Herpes virus, HIV virus, etc.
  2. It is composed of proteins (from virus) and carbohydrates and lipids (from host).
  3. It is made up of smaller subunits called peplomers.
  4. Viruses which do not possess an envelope are called naked viruses.

2. Capsid:

  1. It is the protein coat surrounding the central core of nucleic acid and enzymes (if present).
  2. It consists of specific number and arrangement of small sub-units called capsomers.
  3. They possess antigenic properties.

3. Nucleic Acid:

  1. It is called as nucleiod.
  2. It is the infective part of the virus which utilizes the host cell machinery for the synthesis and assembly of viral components.
  3. For each virus, only one nucleic acid, either DNA or RNA is present.
  4. There are four types of genetic material seen in viruses:

Single stranded DNA (ssDNA) – Coliphage

Double stranded DNA (dsDNA) – Hepatitis-B virus

Single stranded RNA (ssRNA) – Tobacco Mosaic virus (TMV)

Double stranded RNA (dsRNA) – Wound tumour virus

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