VIRUSES ::
These are ultra microscopic obligatory intracellular parasites resistant to antibiotics but susceptible to interferons
Structurally virus consists of a core of nucleic acid which is surrounded by proteinous coat called capsid The whole structure is covered by external lipid membrane called envelop The nucleic acid may be DNA or RNA and accordingly viruses are classified as RNA viruses or DNA viruses Pox virus herpes virus adenovirus etc are the examples of DNA viruses Enterovirus rhinovirus influenza virus mumps measles etc are the examples of RNA viruses
Recently the interest in viral infection has been towards AIDS (Acquired Immuno Deficiency Syndrome ) which is caused by a typical type of virus (retrovirus ) The human immunodeficiency virus type 1(HIV 1) causes AIDS HIV 1 virus carries its genetic message in the form of RNA rather than DNA It carries an enzyme reverse transcriptase which synthesises a single DNA strand in the host based upon the viral RNA code present in the virus
The multiplication of viruses include various steps The virus first gets attached to the host cell membrane (adsorption or attachment ) This is followed by its penetration within the cell once it enters the cell it looses its envelope and capsid (uncoating) the nucleic acid (DNA) undergoes replication (division into two helical chains ) By process of transcription and translation proteins are formed Transcription also forms newer RNA or DNA strands final step is assembling The procapsid which contains RNA or DNA gets covering of protein layer (Capsid) and the envelope (lipid layer) This is new virus
0 Comments