This document discusses RNA viruses. It describes how RNA viruses were discovered and studied using random sequence RNAs. RNA viruses have protein capsids that protect their RNA genomes. Their RNA can be directly used for protein synthesis upon entering a host cell. Retroviruses are a category of RNA virus that use reverse transcriptase to transcribe their RNA into DNA, which can then integrate into the host cell's genome. RNA viruses mutate frequently due to the lack of proofreading by RNA-dependent RNA polymerases during replication, with mutation rates estimated between 10-4 to 10-6 mutations per base pair per generation.

1. RNA VIRUSES

2. HISTORY;
 RNA viruses were discovered The genetic
code was quickly deciphered with Khorana's
synthetic trinucleotides, and a modified form
of methionine (N-formyl-methionine) that
minimally resembled a peptide was found to
initiate protein synthesis in bacteria.
 To study protein synthesis in more detail,
RNAs of random sequence made with
template-independent polynucleotide
phosphorylase were used as ersatz mRNAs.
 Natural mRNAs at the time were hard to get
hold of, especially in intact form, until it was
appreciated that some recently-found
bacteriophages contained RNA genomes that
were also bona fide mRNAs. In contrast to
cellular mRNAs like reticulocyte β-globin,
phage RNA genomes came enclosed in “cast-
iron” capsids that were easy to purify intact,
free of RNase.

3. RNA virus may experience alterations
of between .03 and 2 percent of its
entire genome each year
STRUCTURE
Attachment to the host cell
Penetration
Protective Capsid
Life cycle
RNA present in a virus provide
important consequences in the
life cycle of the virus - and
gives it the potential to outwit
the immune system of host.
lipid envelope
protective
capsid of
protein,
Emergence from the cell

4. RNA viruses invade the human
organism, they inject their RNA
into the cytoplasm of the host
cell. Once they are inside the
cytoplasm, RNA can be used to
synthesize proteins, and,
eventually, to form replica
viruses.
There is a special category of
RNA viruses, which is called
retroviruses.
These viral agents contain
protein known in biology
as reverse transcriptase.
Once the retrovirus injects its
RNA into the cell, reverse
transcriptase transcribes the
RNA into DNA (the operation
that is the reverse of normal
transcription).
• This transcribed viral DNA, once
synthesized, can then be
incorporated into the host cell’s
DNA.
• When the cell replicates, and
eventually divides, it passes down
the viral DNA portion to the
replicated cells.
• One well-known example of the
retrovirus that can infect the human
organism is HIV (Human
immunodeficiency) virus.
RNA DNAREVERSE TRANSCRIPTASE

6. Because RNA viruses are replicated by
RNA-dependent RNA polymerases that
lack proofreading ability, they have the
highest known per bp per generation
mutation rates.
whereas RNA
viruses have
mutation rates of
between 10−4 and
10−6 mutations per
bp per generation
Averaging one mistake per 10,000 nucleotides
each time RNA is copied.
Double-stranded
DNA viruses have
mutation rates of
between 10−6 and
10−8 mutations per
bp per generation,

7. International_Commitee_on_Taxonomy_of Viruses
RabiesMeasles
Parainfluenza
viruses (PIV), and
Respiratory syncytial
virus (RSV),
metapneumovirus
EbolaInfluenza