RNA is a molecule of life, it is present in all living beings and plays a central role in central dogma of life

1. RNA As Molecule Of Life
Presented by
Aanchal Joshi
St. Xavier’s College
(Autonomous) , Ahmedabad
Seminar on

2. •Structure of RNA
•RNA World hypothesis
•RNA as molecule of life
•Functions of RNA
•References

3. RNA is a nucleic acids and is the
major macromolecule essential for all forms
of life. RNA is a polymer of nucleotides
arranged in a chain.
Each nucleotide in RNA contains
• A ribose sugar, with carbons numbered 1' to
5’.
•A base is attached to the 1‘
position, adenine (A), cytosine (C), guanine (G)
or uracil(U) are present. Adenine and guanine
are purines, cytosine and uracil
are pyrimidines.
• A phosphate group is attached to the 3'
position of one ribose and the 5' position of the
next.
RNA

4. The chemical structure of RNA is very similar to that of DNA, but differs in three primary
ways:
• Strandedness
Unlike double-stranded DNA, RNA is a single-stranded, shorter chain molecule. It
posses ability of self complementarity i.e. it base pairs with itself forming intrastrand (i.e.,
single-strand) double helixes, as in tRNA.
• Composition
SUGAR: Unlike DNA which contains deoxyribose, RNA contains ribose as sugar.
It posses a hydroxyl group attached to the pentose ring in the 2’ position. The hydroxyl groups
in the ribose backbone make RNA less stable than DNA because it is more prone
to hydrolysis.
BASE: The complementary base to adenine in DNA is thymine, whereas in RNA,
it is uracil, which is an unmethylated form of thymine.

5. • Uracil is energetically less expensive then thymine (RNA construction happens
1000s of times per minute in a single cell, 1000s of genes are being transcribed into
RNA molecules for many different reasons in cell)
• Using uracil is therefore preferred choice to conserve energy within a cell
• Uracil is abundant in the cell because it is the output of the breakdown of cytosine
• RNA uses the uracil since this C to U mutations are not as harmful in RNA because it
is shorter live and synthesized in greater quantities compared to DNA .

6. •RNA plays a central role in the pathway from DNA to proteins, known as the
"Central Dogma" of molecular biology.

7. •The central dogma of molecular biology explains the flow of genetic
information, from DNA to RNA, to make a functional product, a protein.
• During the process of transcription, a segment of DNA is copied to RNA, or
messenger RNA (mRNA).
• mRNA is the biochemical messenger between the nucleus and the protein
factories called ribosome, present in cell cytoplasm or on the RER.
•tRNA is another type of RNA that helps in decoding the message of the
mRNA by complementarily binding and bringing specific amino acids.
• rRNA present in ribosome forms chains between amino acids via peptide
bonds, building the acids into protein.

8. DNA can also be transcribed into non-coding RNA-
tRNA (transfer): transfer of amino acids to the
ribosome during protein synthesis.
rRNA (ribosomal): essential component of the ribosomes (complex with rProteins).
snRNA (small nuclear): mainly involved in RNA-splicing
(removal of introns).
snoRNA (small nucleolar): involved in chemical modifi-cations of ribosomal RNAs
and other RNA genes.
miRNA (microRNA) : functions in RNA silencing and post-transcriptional
regulation of gene expression.
siRNA (Small interfering RNA ) : promotes the degradation of mRNA at specific
sequences thus prevents the production of specific proteins.

9. DNA makes mRNA makes Protein

10. •The RNA world is a hypothetical stage in the evolutionary history of life on Earth, in
which self-replicating RNA molecules proliferated before the evolution
of DNA and proteins.
•The term RNA world was first used by Walter Gilbert in 1986.
•The RNA world hypothesis is supported by RNA’s ability to store, transmit, and duplicate
genetic information.
• RNA can acts as a ribozyme, a special type of enzyme. Because it can perform the task of
both DNA and enzyme. RNA is believed to have once been capable of supporting
independent life forms and therefore considered as the first molecule of heredity.
•The RNA is much more unstable then DNA. This inherent instability of RNA is a further
limitation to the ability of RNA to account for origin of life.
•As life progressed and evolved over time only DNA, which is much more chemically stable
than RNA, could support large genomes and eventually took over the role as the major
carrier of genetic information.
•RNA enzymes, or ribozymes, are found in today's DNA-based life and could be examples
of living fossils.

11. RNA molecules play an active role within cells by-
• Catalyzing biological reactions.
Example ribozymes function as part of the large subunit
ribosomal RNA to link amino acids during protein synthesis, also in RNA
splicing, viral replication, and transfer RNA biosynthesis.
hammerhead ribozyme, VS ribozyme, Leadzyme and the hairpin
ribozyme.
• Sensing and communicating responses to cellular signals.
RNAs can act as molecular adaptors to connect incoming
analog signals to sequence-specific outcomes. This is exemplified by
‘riboswitches’ which are mRNA elements that alter their structure in
response to ligands, enabling them to sense and react to environmental
parameters

12. • Controlling gene expression and protein synthesis
• Storing heritable information
RNA viruses have genomes composed of RNA that encodes
a number of proteins.

13. •Orgel, L. E. (1998). The origin of life—a review of facts and
speculations. Trends in biochemical sciences, 23(12), 491-495.
•Joyce, G. F. (1989). RNA evolution and the origins of life. Nature, 338(6212),
217.
•https://www.ncbi.nlm.nih.gov/books/NBK26876/
•Orgel, L. E. (2003). Some consequences of the RNA world hypothesis. Origins
of Life and Evolution of the Biosphere, 33(2), 211-218.