question_answer 11)

Give a brief account of viruses with respect to their structure and nature of genetic material. Also name four common viral diseases.

Answer:

Viruses are non-cellular, ultramicroscopic, infectious particles. They are made up of envelope, capsid, nucleoid and occasionally one or two enzymes. Viruses possess an outer thin loose covering called envelope. The central portion of nucleoid is surrounded by capsid that is made up of smaller sub-units known as capsomeres. The nucleic acid present in the viruses is known as nucleoid. It is the infective part of the virus which utilises the host cell machinery. The genetic material of viruses is of four types— (i) Double stranded DNA (dsDNA) as found in pox virus, hepatitis-B virus and herpes virus, etc. (ii) Single stranded DNA (ssDNA) occur in coliphage fd, coliphage f x174. (iii) Double Stranded RNA (cteRNA) occur in Reo virus, (iv) Single stranded RNA : (dsRNA) occur in TMV virus, polio virus, etc. Four common viral diseases are (i) Polio, (ii) AIDS, (iii) Hepatitis-B, (iv) Rabies.