Structurally viruses are made up of envelope, capsid, nucleoid and occasionally one or two enzymes.
(i) Envelope : Some viruses possess an outer thin loose covering, called envelope. It is composed of proteins (from virus), lipids and carbohydrates (both from host). The smaller subunits of envelope are called peplomers. Envelope is mainly found in some animal viruses (e.g., Herpes Virus, HIV, Influenza virus, Rous sarcoma virus) and rarely in some plant viruses (e.g., Potato yellow dwarf virus) and bacterial viruses (e.g., Pseudomonas Z). The viruses, which do not possess envelope, are called naked.
(ii) Capsid : It is the protein coat that surrounds the central portion of nucleoid and enzymes (if present). The capsid consists of a specific number and arrangement of small sub-units called capsomeres. These sub-units possess antigenic properties.
(iii) Nucleoid : The nucleic acid present in the virus is called nucleoid. It is the infective part of virus which utilizes the metabolic machinery of the host cell for synthesis and assembly of viral components. The genetic material of viruses are of four types :
(a) Double stranded DNA (ds DNA) : Occur in Herpes virus, Pox virus, Cauliflower mosaic virus (linear), Hepatitis–B virus (circular).
(b) Single stranded DNA (ss DNA) : Occur in Coliphage fd (linear), coliphage (cyclic).
(c) Double stranded RNA (ds RNA) : Occur in Reo virus, wound tumour virus.
(d) Single stranded RNA (ss RNA) : Occur in Tobacco mosaic virus, Influenza virus, Foot and Mouth virus, Polio virus, Retroviruses (e.g. HIV), etc.
Structurally viruses are made up of envelope, capsid, nucleoid and occasionally one or two enzymes.
(i) Envelope : Some viruses possess an outer thin loose covering, called envelope. It is composed of proteins (from virus), lipids and carbohydrates (both from host). The smaller subunits of envelope are called peplomers. Envelope is mainly found in some animal viruses (e.g., Herpes Virus, HIV, Influenza virus, Rous sarcoma virus) and rarely in some plant viruses (e.g., Potato yellow dwarf virus) and bacterial viruses (e.g., Pseudomonas Z). The viruses, which do not possess envelope, are called naked.
(ii) Capsid : It is the protein coat that surrounds the central portion of nucleoid and enzymes (if present). The capsid consists of a specific number and arrangement of small sub-units called capsomeres. These sub-units possess antigenic properties.
(iii) Nucleoid : The nucleic acid present in the virus is called nucleoid. It is the infective part of virus which utilizes the metabolic machinery of the host cell for synthesis and assembly of viral components. The genetic material of viruses are of four types :
(a) Double stranded DNA (ds DNA) : Occur in Herpes virus, Pox virus, Cauliflower mosaic virus (linear), Hepatitis–B virus (circular).
(b) Single stranded DNA (ss DNA) : Occur in Coliphage fd (linear), coliphage (cyclic).
(c) Double stranded RNA (ds RNA) : Occur in Reo virus, wound tumour virus.
(d) Single stranded RNA (ss RNA) : Occur in Tobacco mosaic virus, Influenza virus, Foot and Mouth virus, Polio virus, Retroviruses (e.g. HIV), etc.