This document discusses RNA genomes and their replication. It begins by defining RNA and noting that some viruses and certain bacteria use RNA as their genetic material rather than DNA. It then discusses how RNA replicates, noting that RNA viruses encode an RNA-dependent RNA polymerase to copy their genomes. The replication of positive-sense, negative-sense, and double-stranded RNA viruses is explained. Retroviruses are provided as an example of viruses that replicate through a DNA intermediate using the enzyme reverse transcriptase. In summary, the document outlines the key differences between RNA and DNA genomes and explains the mechanisms that RNA viruses use to replicate.

1. Duration: 15 min M.Sc Biotechnology 1st Semester SUBJECT-Molecular Biology
RNA GENOME AND ITS
REPLICATION
MADE BY- SARAH HAMID
M.Sc BIOTECHNOLOGY
PGY-1

2. (1)What is RNA?
(2)How does it replicates?
(3)Which organisms have RNA as their genome
Genome, virus, RNA, Reverse Transcriptase
Learning objectives
Keywords
Presentation’s overview
(1)Understanding RNA
(2)Replication mechanism of RNA viruses
(3)Important enzymes for viral RNA replication

3. 1. What is a genome?
2. What is RNA?
A genome is an organism’s complete set of genetic
instructions. Each genome contains all of the information
needed to build that organism and allow it to grow and
develop.
A nucleic acid similar in structure and properties to DNA,
but it only has a single strand of bases and instead of the
base thymine (T), RNA has a base called uracil (U).
RNA was the first genetic material. There is now enough
evidence to suggest that essential life processes (such as
metabolism, translation, splicing, etc.), evolved around
RNA. RNA used to act as a genetic material as well as a
catalyst (there are some important biochemical reactions
in living systems that are catalysed by RNA catalysts and
not by protein enzymes).
2. What is RNA?

4. But, RNA being a catalyst was reactive and hence unstable. Therefore,
DNA has evolved from RNA with chemical modifications that make it more
stable. DNA being double stranded and having complementary strand
further resists changes by evolving a process of repair.

5. 3. RNA as a genome
“RNA is a source of information, a genetic material, which sends
information towards the host cell to exploit it and reproduce within
it, thus creating more of its copies. These copies do this same
process again and again, growing in numbers numerously. RNA can be
therefore interpreted as a “brain” or “information carrier”
• Viruses are tiny particles that can infect not only humans, but also
plants and animals and cause them a disease.
• Viruses are created of a genetic material RNA, which is protected
by a protein wrapping.
• Viruses abduct specific cells of living organisms. Their insert their
genetic information into the cell, overwrite it and take control. Cell
becomes an unwilling host, which is forced to make more viruses and
spread them to infect them further.
• As more and more cells are infected, the immune system starts to
tackle them and signs of health issues occur. With the Flu, it can
be sneezing, headache, raised temperature.

6. 4.ORGANISMS HAVING RNA AS A GENOME
• The organisms that have RNA as their
genome include several viruses. The viruses
include- poliovirus, HIV, and several plant
viruses(tobacco mosaic virus and barley
yellow dwarf virus).
• Some bacteriophages also have RNA as
their genetic material.

7. 5. Difference between DNA and RNA

9. 6. RNA REPLICATION
• RNA replication is the process by which new copies of genome-length RNAs are made.
• RNA replication occurs in the cytoplasm and is carried out by the viral RNA polymerase.
The full length plus strand is coated with nucleocapsid protein as it is made (mRNAs are not coated
with this protein, which would interfere with the host protein translation machinery).
• The new positive strand is copied into full length minus strand, which is also coated with nucleocapsid
protein as it is made.
• Replication of an RNA target sequence results from continuous cycles of Reverse
transcription and RNA transcription by means of cDNA intermediates
• Viruses also reproduce, but they cannot do so on their own. That is why they cannot be called “alive” in
the strictest sense of the word.

10. 6. RNA replication contd..
• They use the replication apparatus of the host cells, and have
additionally developed a number of special characteristics.
• Scientists differentiate viruses according to the genome type –
there are DNA and RNA viruses: viruses may have single-stranded
or double-stranded linear RNA, single-stranded or double-stranded
linear DNA, single-stranded or double-stranded circular DNA and
other variations.
• Some viruses contain some of the enzymes required for their
replication, for example the influenza virus, whose envelope not only
contains an RNA genome but also an RNA polymerase. When the
virus enters the host cell, the enzyme RNA polymerase starts to
replicate the viral genome.
• The synthesis of the genome of DNA viruses usually begins at a
replication origin that binds specific initiator proteins, which recruit
replication enzymes of the host cell which then replicate the viral
genome.

11. • Plus-stranded RNA viruses- the same as mRNA
and functions as mRNA.
• Negative-stranded RNA viruses- complementary
to mRNA and need to be copied to plus-sense
mRNA.
• Double-stranded RNA viruses- cannot function as
mRNA and need RDRP.

12. BALTIMORE CLASSIFICATION SYSTEM
• There are 2 types of RNA viruses-
(1)Virus that have DNA intermediates in
their replication cycle(group Vl)
(2)Virus that do not have a DNA
intermediate in their replication
cycle(group lll, lV and V)

13. REPLICATION STRATEGIES IN VIRUS
(a)RNA virus that do not have a DNA phase
These viruses have RNA intermediates, hence
they need an enzyme called RDRP(RNA
dependent RNA polymerase) to replicate their
RNA.
These viruses have RDRP packaged along with
their genome as the host animal cells do not
code for this enzyme.
(1)Positive-stranded RNA viruses- These can
directly act as mRNA and carry out the
process of translation. For e.g. Poliovirus
(2)Negative-stranded RNA viruses- These
cannot directly act as mRNA and first have to
transcribe the plus sense strand which then
carries out the process of translation. For e.g.
Ebola virus

14. (b) Viruses which have a DNA phase
• Best example for such type of viruses are
the Retroviruses.
• These viruses are positive-stranded RNA
viruses still it doesn't act as mRNA rather
they have a special enzyme i.e. Reverse
Transcriptase which reverse transcribes the
viral RNA into a complementary
DNA(cDNA).
• This cDNA is then integrated into the host
genome(DNA) with the help of the enzyme-
Integrase.
• This is called as provirus.
• Now the virus takes over the host’s
machinery to make more viral particles.

15. • https://www.microbiologybook.org/
• https://www.youtube.com/
• https://microbenotes.com/
• https://www.ncbi.nlm.nih.gov/
• https://courses.lumenlearning.com/
• Book- NCERT(Biology) class 12th
REFERENCES