RNA is a molecule that is present in most living organisms and viruses. It is made up of nucleotides containing ribose sugars attached to nitrogenous bases and phosphate groups. There are three major types of RNA: messenger RNA (mRNA) which carries DNA instructions to the ribosome, ribosomal RNA (rRNA) which forms the ribosome where protein synthesis occurs, and transfer RNA (tRNA) which transports amino acids to the ribosome during protein synthesis. The document further describes the structure, function and roles of mRNA, rRNA, tRNA as well as other types of RNA like microRNA. It also explains the wobble hypothesis regarding degeneracy in the genetic code.

1. RIBONUCLEIC ACID
(RNA)
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2. RNA
• Ribonucleic acid (RNA) is a molecule that is present in the majority of living organisms
and viruses. It is made up of nucleotides, which are ribose sugars attached to
nitrogenous bases and phosphate groups. The nitrogenous bases include adenine,
guanine, uracil, and cytosine. RNA mostly exists in the single-stranded form, but there
are special RNA viruses that are double-stranded. The RNA molecule can have a variety
of lengths and structures. An RNA virus uses RNA instead of DNA as its genetic material
and can cause many human diseases. Transcription is the process of RNA formation
from DNA, and translation is the process of protein synthesis from RNA. The means of
RNA synthesis and the way that it functions differs between eukaryotes and
prokaryotes. Specific RNA molecules also regulate gene expression and have the
potential to serve as therapeutic agents in human diseases.
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3. A general structure of RNA
It is made up of nucleotides, which are ribose sugars attached to nitrogenous bases and phosphate groups. The
nitrogenous bases include adenine, guanine, uracil, and cytosine.
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4. Three major forms of RNA
1. Messenger RNA (mRNA)
2. Ribosomal RNA (rRNA)
3. Transfer RNA (tRNA)
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5. OTHER FORMS OF RNA......
Small nuclear RNA (SnRNA)
Micro RNA (Mi RNA)
Small interfering RNA (Si RNA)
Teleomerase RNA component
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6. Messenger RNA (mRNA)
Formed in the nucleus as the complementary strand for the gene that is to be expressed. This
step is called transcription, since the protein message is being written out as mRNA. After the
gene's code is written, mRNA takes the code out to a ribosome to be translated. The code is used
to put amino acids in the correct order to build the correct protein
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7. Function of mRNA;
• - mRNA makes up about 5% of the total RNA composition of the cell
• - mRNA serves as a template for protein synthesis in a process called translation
• - in eukaryotes a distinct mRNA molecule is produced for each gene
• - in prokaryotes mRNA molecules code for several genes
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8. RIBOSOMAL RNA (rRNA)
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9. Ribosomes are composed of a large subunit called the 50S and a small
subunit called the 30S, each of which is made up of its own specific
rRNA molecules. Different rRNAs present in the ribosomes include
small rRNAs and large rRNAs, which belong to the small and large
subunits of the ribosome, respectively rRNAs combine with proteins
and enzymes in the cytoplasm to form ribosomes, which act as the site
of protein synthesis.
It is Formed into ribosomal subunits in the nucleolus of the nucleus.
Once formed, they are shipped out to the cytoplasm to begin
translating mRNA sequences into proteins. To translate an mRNA
code, a small and a large ribosomal subunit must combine to make a
complete ribosome. When finished, the subunits detach and seek out
another mRNA strand to decode.
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10. Function
-rRNA makes up about 80% of the total cellular RNA
-rRNA is a major constituent of the ribosomes
-rRNA gives the ribosome its structure and also plays a catalytic role
-Prokaryotes have 3 varieties of rRNA: 5S, 16S and 23S rRNAs(The 5S and 23S rRNAs are
found within the large ribosomal subunit, while the 16S rRNA is located in the small
ribosomal subunit)
-Eukaryotes have four types of rRNA: 3 species in the LSU and 1 in the SSU.
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11. TRANSFERE RNA (tRNA)
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12. • tRNA is the smallest of the 3 types of RNA, possessing
around 75-95 nucleotides. tRNAs are an essential
component of translation, where their main function is the
transfer of amino acids during protein synthesis. Therefore,
they are called transfer RNAs.
Each of the 20 amino acids has a specific tRNA that binds
with it and transfers it to the growing polypeptide chain.
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13. FUNCTION;
• Transfer RNA, abbreviated tRNA, brings amino acids to the ribosome.
There are sixty-four possible formations of tRNA, and each tRNA is
bonded to a specific amino acid. The ribosome matches the tRNA code
to the mRNA code to build the correct sequence of amino acids. Like
rRNA, the tRNA molecules are reusable, so once they drop off their
assigned amino acid, they can go pick up another one.
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14. Function cont…..
• -tRNA makes about 15% of the total cellular
RNA
• -Each amino acid has at least one tRNA made
specifically to carry it to the ribosome
• - this form of RNA has a distinct stem-loop
structure and functions in carrying activated
amino acids to the ribosome
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15. THE WOBBLE HYPOTHESIS
• The Wobble Hypothesis explains why multiple codons can code for a
single amino acid. One tRNA molecule (with one amino acid
attached) can recognise and bind to more than one codon, due to the
less-precise base pairs that can arise between the 3rd base of the
codon and the base at the 1st position on the anticodon. This hence
explains why more codons exist than there are specific tRNA
molecules. The Wobble Hypothesis also illustrates why the only
variability between many codons, that encode the same amino acid,
is their 3rd base.
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16. • • Crick (1996) proposed the 'wobble hypothesis' to explain the
degeneracy of the genetic code.
• • Except for tryptophan and methionine, more than one codons direct
the synthesis of one amino acid.
• • There are 61codons that synthesis amino acids, therefore, there
must be 61 tRNAs each having different anticodons. But the total
number of tRNAs is less than 61.
• • This may be explained that the anticodons of some tRNA read more
than one codon.
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17. • • In addition identity of the third codon seems to be unimportant. For
example CGU, CGC, CGA and CGG all code for arginine.
• • It appears that CG specifies arginine and the third letter is not
important. Conventionally the codons are written from 5'end to 3'end.
• • Therefore the first and second bases specify amino acids in some
cases.
• • According to the wobble hypothesis only the first and second bases of
the triple codon 5‘→3' mRNA pair with the bases of the anticodon of
tRNA, i.e., A with U or G with C.
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18. • • The pairing of the third base varies according to the base at this
position for example G may pair with C the convention pairing [A =U ,
G=C] is known as wotson - Crick pairing and the second abnormal
pairing is called wobble pairing.
• • This was observed from the discovery that the anticodon
of Yeast alanine tRNA contains the nucleoside inosine in the
first position[ 5'→3'] that paired with the third base of the codon
[5'→3'].
• • Inosine was also found at the first position in other tRNA.
e.g. isoleucine and serine.
• • The purine inosine is a wobble nucleotide and is similar
to guanine which normally pairs with A, U,G, and C.
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19. The significance of the Wobble
• Our bodies have a limited amount of tRNAs and Wobble allows for
broad specificity.
• Wobble base pairs have been shown to facilitate many biological
functions, most clearly proven in the bacterium Escherichia coli.
• The thermodynamic stability of a wobble base pair is comparable to
that of Watson-crick base pair.
• Wobble base pairs are fundamental in RNA secondary structure and
are critical for the proper translation of the genetic code.
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20. Significance cont......
• Wobbling allows faster dissociation of tRNA from mRNA and also
protein synthesis.
• The existence of Wobble minimizes the damage that can be caused by a
misreading of the code; for example, if the Leu codon CUU were
misread CUC or CUA or CUG during transcription of mRNA, the codon
would still be translated as Leu during protein synthesis.
• Relation to redundancy
• The genetic code is redundant whereby several different codons code
for the same amino acid. Often, this redundancy is specified in the
third codon position such that several codons with the same first two
nucleotides, but different third position nucleotides, code for the same
amino acids.
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21. Revised pairing rules;
tRNA 5' anticodon base mRNA 3' codon base
G U,C
C G
k2C A
A U,C,(A),G
unmodified U U,(C),A,G
xo5U U,A,G
I A,C,U
•
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22. In Conclusion;
mRNA tRNA rRNA
definitions Sub type of the RNA molecule that
carries a portion of the DNA code
to other parts of the cell for
processing
Helps in decoding mRNA series
into a protein
It is called the cells protein factory
and is the component of the
ribosome
Shape Linear shaped Clover shaped Sphere shaped
3D in appearance
Function carries a portion of the DNA code
to other parts of the cell for
processing
It is a small RNA molecule
responsible for transferring amino
acids in the cytoplasm to the
ribosome
Forms the ribosomes and serves as
the structure of translation
Codons or Anti codons Codons are present Anti codons are present Neither codons nor anti codons are
present
Size Typically 400-12000 nucleotides in
mammals
76-90 nucleotides Size can either be 30S,40S,50S and
60S
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23. BIBLIOGRAPHY:
• P. Ahlquist, RNA-dependent RNA polymerases, viruses, and RNA silencing, Science, 296:1270–
1273, 2002 DOI:
• http://doi.org/10.1126/science.1069132 B. Alberts et al., Molecular Biology of the Cell, 5th ed.,
Garland Science, New York, 2008
• P. P. Amaral et al., The eukaryotic genome as an RNA machine, Science, 319:1787–1789, 2008
DOI:
• http://doi.org/10.1126/science.1155472 B. L. Bass (ed.), RNA Editing, Oxford University Press,
Oxford, U.K., 2001
• T. R. Cech, Crawling out of the RNA world, Cell, 136:599–602, 2009 DOI:
http://doi.org/10.1016/j.cell.2009.02.002
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24. THANK YOU SO MUCH FOR
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