Viruses
A viruses is a
non-cellular particle made up of genetic material and protein that can invade
living cells.
Sub microscopic
entity consisting of a single nucleic acid surrounded by a protein coat and
capable of replication only within the living cells of bacteria, animals or
plants.
Discovery
The scientific
study of viruses and the infections they cause – began in the closing years of
the 19th century. Although Louis Pasteur and Edward Jenner developed the
first vaccines to protect against viral infections, they did not know
that viruses existed. The first evidence of the existence of viruses came from
experiments with filters that had pores small enough to retain bacteria. In
1892, Dmitry
Ivanovsky used one of
these filters to show that sap from a diseased tobacco plant remained
infectious to healthy tobacco plants despite having been filtered. Martinus Beijerinck called the
filtered, infectious substance a "virus" and this discovery is
considered to be the beginning of virology. The subsequent discovery and
partial characterization of bacteriophages by Felix d'Herelle further catalyzed the field, and by the early 20th
century many viruses were discovered.
Dmitry Ivanovsky
Martinus Beijerinck
Felix d'Herelle
Characteristics
They are enclosed in a protective envelope.
They have spikes, which helps them to attach to the host
cell.
They are non cellular.
They do not respire, do not metabolize and do not grow
but they do reproduce.
They contain a protein coat called the Capsid.
They have
a nucleic acid core containing DNA or RNA.
Ribosomes and enzymes are absent, which are needed for
metabolism.
They are considered both as living and non living
things, as viruses are inactive when they are present outside of host cells and
are active in side of host cells. As they make use of raw materials and enzymes
of the host cell to reproduce and causes several infections.
Most virus infect only specific host cell.