This document provides information about RNA and different types of RNA. It discusses that RNA, like DNA, is composed of nucleotides joined by phosphodiester bonds, but contains ribose instead of deoxyribose and uracil instead of thymine. There are two main types of RNA - genetic RNA that acts as the genetic material of some viruses, and non-genetic RNA involved in protein synthesis, including messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). The document describes the structure and functions of mRNA and tRNA in protein synthesis.

2. PRESENTED BY
Dr. N. Sannigrahi, Associate Professor
Department of Botany
Nistarini College, Purulia (W.B) India

3. INTRODUCTION
The world of DNA is fascinating but the puzzle of the RNA world is not less
fascinating than the DNA. Have you heard about some common diseases of
human beings like paralytic poliomyelitis, common cold, Hand-foot-mouth
disease, Aseptic meningitis, Mild acute hepatitis, Acute gastroentitis , yellow
fever, Dengue, Encephalitis, SARS, AIDS, T-cell leukemia, Measles, Mumps,
Rabies, recent epidemic of COVID 19 and many more. These are all about the
examples of human communicable diseases caused by the virus having the
genetic material , RNA . Do you have an interest in genome editing technology
and molecular medicine for higher learning? Can be applied to a broad range of
scientific questions such as: Gene expression profiling between samples. study
of alternative splicing events (differential inclusion/exclusion of exons in the
processed RNA product after splicing of a precursor RNA segment) associated
with diseases. You want to make garlands of the diverse types of flowers of
different combinations . Immediately, you do need a blue print and on the basis
of the message encrypted there to make the garlands. Some agents required to
assemble the flowers in this regard. The language of DNA is converted into the
language of proteins by the dint of the another non-genetic materials like mRNA,
tRNA etc. All these genetic and non-genetic material of nucleic acid makes the
awesome RNA world.

4. RNA VIRUS

5. RIBONUCLEIC ACID ( RNA)
RNA , like DNA , is a long, unbranched macromolecule consisting of
nucleotides joined by 3-5 phosphodiester bonds. The number of nucleotides in
RNA ranges from as few as 75 to many thousands.
RNA ,molecules in the cytoplasm may be associated with ribosome. Each
ribonucleotiudes has three components-
Ribose sugar,
Nitrogenous bases (Adenine, Guanine, Cytosine & Uracil)
Phosphoric acid.
These structures are similar to DNA except that instead of deoxyribose sugar,
ribose sugar and instead of Thymine, Uracil present in RNA.
In addition to those basic differences , the following points must be accounted
of as stated below:
i. As apparent from the name. the sugar moiety in RNA , to which the
phosphate and the nitrogen bases are attached, is ribose rather than 2-
deoxyribose of DNA. Ribose contains a 2-carboxyl group not present in
deoxyribose.

6. ii. RNA contains the pyrimidine Uracil (U) in place of thymine which is the
characteristic of DNA molecule. However, it lacks the methyl group
present in thymine. But it may be noted that , however, RNA possess
thymine.
iii. The RNA is single stranded rather than double stranded helical structure
of DNA. However, given complementary base sequence with opposite
polarity, the single stranded RNA may fold back on itself like a
hairpin and thus acquire the double stranded pattern. In the region of
hairpin loop, A pairs with U and G pairs with C. Guanine can also pair
with Uracil but is less strong than G-C pair. The base pairing in RNA
hairpins is frequently imperfect. Some of the opposing bases may not
be complementary and one or more bases along a single strand may
be looped out to facilitate the pairing of the others. The proportion of
helical region in various types of RNA varies over a wide range,
although a value of 50% is typical.
iv. RNA molecule is single stranded and complementary to only one of the
two strands of gene, it need to have complementary base ratios,

8. In other words, its adenine content does not necessarily equal to its Uracil
content, nor does it Guanine content necessarily equal its Cytosine content . In a
word, it does not maintain Chargaff’s rule as far as base sequence and other rules
applicable for DNA is concerned.
v. RNA is hydrolyzed by weak alkali (pH 9 at 100℃) to 2′ -3′ – cyclic diesters
of the mononucleotides via an intermediate compound called 2′ , 3′ , 5′ -triesters.
This intermediate , however, can not be formed in alkali-treated DNA because of
the absence of a 2′ -hydroxyl group in its molecule. Thus. RNA is alkali-labile
whereas DNA is alkali-stable.
vi. Base pairing takes place in only the helical regions of the RNA molecule,
which amount to roughly half (50%) of the entire RNA molecule.
vii. RNA does not act as template for its synthesis,
vii. RNA exhibits complete and practically instantaneous reversibility of the
process of melting,
viii. RNA does not undergo mutation usually like DNA ,
ix.RNA is stained red with pyronin.

9. TYPES OF RNA
Depending upon the hereditary information, RNA may be two types-
i. GENETIC OR GENOMIC RNA- Where RNA acts as genetic material
like Riboviruses or viroid. In viroids, RNA has both genetic and catalytic
function. Genetic RNA is single stranded in most of the cases like TMV,
HIV, and is double stranded like Reovirus, wound tumor virus etc.
ii. NON-GENETIC RNA- RNA molecule does not acts as genetic material.
Rather they are associated with protein synthesis as a part of the central
dogma of the molecular basis of life. They are almost all synthesized from
DNA by the process of transcription and enjoys a wide diversity as stated
below as far as structure and function.
a. mRNA or informational RNA or Template RNA- The abundance of RNA
in the cytoplasm and its role in protein synthesis suggests that the genetic
information of nuclear DNA is transmitted to an RNA which function in
the sites of protein synthesis. As par Jacob & Monod, the mRNA should
have the following properties-
The messenger should be polynucleotide,
The base composition of the messenger should reflect the base
composition of the DNA that specifies it.

11. The mRNA should be very heterogeneous in size because of genes or groups
of genes. Vary in length. They are correctly assumed that 3 nucleotides code
for the amino acid and that the molecular weight of an mRNA should be at
least a half million.
The messenger should be , for a short period, associated with ribosome,
The messenger should be synthesized and degraded very rapidly.
All these properties are nowadays ascribed to the mRNA because the other 2
types of RNAs are homogenous and also their base composition is similar is
species that have very different base ratio.
mRNA is most heterogeneous in size and stability among all types of RNAs
having molecular weight 5,00,000 to 20,00,000 and it constitutes only about
5% of the total RNAs. The mRNA may be monocistronic carrying
information for single polypeptide or polycistronic carrying information for
many polypeptides. Some proteins contain less than 100 amino acids , mRNA
coding for those proteins must have at least 100*3=300 or more nucleotide
residues. In E. coli, average size of the mRNA is 900-1500 nucleotide units.
Half life of mRNA in bacteria may be a few seconds to about 2 minutes while
in mammalian system, it ranges from few hours to one day.

13. mRNA s are single stranded and complementary to the sense strand of the
respective structural genes The prokaryotic and eukaryotic mRNA have some
sorts of differences. In eukaryotes, mRNA molecule immediately acquires 5′ cap
which is a part of the structure recognized by the small ribosomal subunit. Protein
synthesis begins at the start codon near 5′ end of the mRNA. The 5′ end of the
mRNA is capped by a 7-methylguanosine triphosphate which is linked to an
adjacent 2′-o-methylribonucleoside at its 5′ hydroxyl through the 3 ′phosphates.
The function of the capping of mRNA is not well understood, the cap is probably
involved in the recognition of the mRNA by the translating machinery. The
translation of the mRNA into protein begins at the capped 5′ end. The other end of
the most mRNA molecules , the 5′ hydroxyl end , has attached a polymer of
adenylate residues, 20-250 nucleotides in length. The mRNA also constitutes
initiation codon (AUG or GUG), coding regions have numerous triplet codons and
in the end , termination codon (UAA, UAG and UGA). mRNA is more rapidly
produced in cell but exists much shorter period than rRNA & tRNA. So, for short
life span, mRNA is least amount available in cell than others and mRNA is
dismantled immediately after it has been used for the synthesis of a particular
protein for which it was once synthesized.

14. TRANSFER RNA(tRNA)
Transfer RNA is the smallest RNA with molecular weight from 23000-30000,
consists of 15% of the total cell RNA and more stable than mRNA. They
basically involved in the transfer of amino acids from the cytosol to the site of
the protein synthesis i.e. the specific codons of mRNA on ribosome. tRNA as
first discovered by Hoagland et al. (1957) with 4S value bearing 70-85
nucleotides which is folded over itself forming a clover leaf like (Holley et
al., 1964, two dimensional) or L shaped (Klug, 1974, three dimensional
structure).
STRUCTURE
A clover leaf model has the following characteristics
1. It has four main arms or sites excluding a fifth small arm called extra arm
or blind lump,
2. The four arms are – Acceptor arm or amino acid binding site, Anti-codon
site or Loop, Aminoacyl synthetase Binding Loop (DHU arm), Ribosomal
Binding Loop (TφC Loop).

15. 2. All tRNA molecules are unbranched chains consisting of 73-93
ribonucleotide residues, corresponding to molecular weighs between 24000 and
31000,
3. All tRNA contain from 7-15 unusual modified bases. Many of these unusual
bases are methylated or dimethylated derivatives of A,U, G and C. These
include nucleotides of pseudouridine , various methylated adenines and
Guanines , methylated pyrimidine such as thymine and 5-methylcytosine and
others. Not all these are present in any one source of tRNA but pseudouridine
(φU)is the most abundant and universally distributed. The role is uncertain but
assume to perform the following two functions-
i. Methylation prevents the formation of certain base pairs so that some of the
bases become accessible for other interactions,
ii. Methylation imparts hydrophobic character to some portions of tRNA
molecules which may be important for the interactions with the synthetase and
with ribosomal proteins.
4. The 5′ end of tRNA is phosphorylated . The 5′ terminal residue is usually
guanylate (pG)
5. The base sequence at the 3′ end of all tRNAs is CCA. All amino acids binds
to this terminal adenosine via 3′-OH group of its ribose. (5′ end)----G------
tRNA---CCA (3′ end)

16. 6. About 50% of the nucleotides in tRNAs are base paired to form double helices.
The conventional numbering of the nucleotides begins at the 5′ end and toward at
the 3′ end . In all tRNAs , the nucleotides at the 3′ end contains the sequence of
CCA. Certain locations can have additional nucleotides that are not found in all
tRNAs molecules.
7. There are, however, 5 groups of bases which are not base-paired. These 5
groups, of which 4 form ‘loops’ are :
a. The 3′ CCA terminal region,
b. The ribothymine – pseudouracil-cytosine (= TφC) loop,
c. The ‘extra arm’ or little loop, which contains a variable number of residues,
d. The dihydrouracil (=DHU) loop, which contains several dihydrouracil residues
, and
e. The anti-codon loop, which contains of 7 bases with sequence , 5′-Pyrimidine-
pyrimidine-X-Y-Z-modified purine - variable base-3′. The loop contains a triplet
of bases which allows the tRNA to hydrogen bond to a complementary sequence
on mRNA attached to ribosome.
8. The four loops are recognition sites. Each tRNA must have at least two such
recognition sites; One for the activated amino-acid enzyme complex with which
it must react to form the amino-acyl-activated amino acid enzyme complex with
which it must react to form the aminoacyl-tRNA and other for the site on the

18. A messenger RNA molecule which contains the code for that particular amino
acid. It is interesting to note that the former involves recognition by bases of
amino acid residues or of a site on the enzyme molecule whereas the latter
involves recognition by bases of bases (hydrogen bonding).
9. A unique similarity among all tRNA molecules is that the overall distance
from CCA at one end to the anti-codon at the other end is constant. The
differences in nucleotide numbers in various tRNA molecules is, in fact,
compensated for by the size of the ‘extra arm’ which is located between the
anti-codon loop and Tφ C loop.
THREE DIMENSIONAL STRUCTURE OF tRNA
Rich & Klug (1960) on the basis of X-ray crystallography have elucidated the
three dimensional structure of tRNA as follows:
i. The molecule is L-shaped,
ii. There are two segments of double helix, each of the helix contains 10
base pairs which corresponds to one turn of the helix and they are
perpendicular to each other,
iii. The CCA terminus containing the attachment site for the amino acid is
one at one end of the L. The other end of the L is occupied by the
anticodon loop. The DHU and T φ C loops from the corner of the loop,

19. iv. The CCA terminus and the adjacent helical region do not interact strongly with
the rest of the molecule and may change conformation with respect to amino
acids
RIBOSOMAL RNA ( rRNA)/INSOLUBLE RNA
It is the component of ribosome. The rRNA molecule appears as a single
unbranched polynucleotide chain and the structures depends upon ionic
strength. Ribosome has two sub units- smaller & larger having different
sedimentation coefficient values in prokaryotes and eukaryotes. In both the
subunits, rRNA is present being coiled in between and over protein
molecules. The rRNA is four types as far as sedimentation coefficient
values- 28S (23S in prokaryotes), 18S ( 16S in prokaryotes), 5.8S ( absent in
prokaryotes) and 5S. The 28S, 5.8S, and 5S rRNA in eukaryotes occur in
larger subunits but 18S rRNA occur in smaller sub units of ribosome. rRNA
is formed in the nucleolus region of eukaryotes. rRNA constitutes about
80% of the total RNA of the cell. Its molecular weight ranges from 35000-
10,00,000. rRNA is involved in protein synthesis. Different types of rRNA
have different functions.18S rRNA provides binding site to mRNA and 5S
rRNA has a similar site for tRNA. rRNA is more stable than mRNA.

21. DIFFERENT OTHER RNAs
In addition to these three major RNAs , there are other types of RNAs which
also deserve understanding in this regard for the clear understanding of the RNA
found in the nature. They are as follows:
Small Nuclear RNA (snRNA)- It is a small Uridine rich RNA that occurs inside
the nucleus. It is associated with 7-8 molecules of proteins and takes part in
splicing and processing of other RNAs.
Small Cytoplasmic RNA (scRNA)- It is also small RNA present in the
cytoplasm. It helps in the processing of polypeptides.
Micro-RNA (miRNA)- It is a small non-coding RNA containing about 32
nucleotides and found in plants, animals and virus. It plays important role in
mRNA silencing and post-transcriptional regulation of gene expression. The
human genome may encode over 1000 miRNAs.
Small interfering RNA ( siRNA)- The RNA derived from longer regions of
double stranded RNA.
Guide RNA (gRNA)- Synthesized from mtDNA and used for RNA editing

22. Short Hairpin RNA ( shRNA)- In artificial RNA used fro gene silencing.
Antisense RNA- Inhibit translation process
HETEROGENOUS NUCLEAR RNA ( hnRNA)
In mammalian cells including human beings, a precursor RNA is synthesized in
the nucleoplasm by DNA-dependent RNA polymerase. This precursor is
degraded by a nuclear nuclease to mRNA that is then translocated to the
cytoplasm where it becomes associated to the ribosomal system. This precursor
RNA constitutes the another class of RNA molecules and it is designed as
heterogeneous nuclear RNA ( hnRNA). The hnRNA molecules may have high
molecular weight whereas the mRNA has least molecular weight. Most
mammalian mRNA molecules are 400-4000 nucleotides in length but hnRNA
molecules possess 5000-50,000 nucleotides. Some uncertainty still exist
concerning the precursor product relationship between hnRNA and
mRNA..The hnRNA molecules appear to be processed to generate the mRNA
templates for protein synthesis.
It has been recently found that RNA not only carries blueprint message from
imperious DNA to the factories that churn out proteins but it could catalyze the
reactions that protein enzyme do. The Ribozyme has been derived from that
and this has lead the concept of RNA world.

23. FUNCTIONS OF RNA
The RNA plays important role in the molecular biology of the cell structural and
functional attributes and play a very crucial role in the following issues.
Genetic RNA- These RNAs act as hereditary information of different viruses
and viriods and play crucial role for keeping up the genetic information in this
regard.
RNA as primer- The autocatalytic function of DNA is initiated by the uses RNA
as primer for the faithful replication of DNA.
In Ribosome- rRNA acts as the constituents of ribosome to perform the
multifold functions in different cellular activities.
Role of Genetic Code- mRNA bears the codon which carry genetic messages
from DNA and later on undergoes translation as a language of protein.
Polypeptide Processing- It is carried out by small cytoplasmic RNA and plays a
very important role in this regard.
RNA enzyme- Ribozyme, a non-protein enzyme is made up of RNAs
Ribonuclease-P and peptidyltransferase enzymes are also made up of RNAs
RNA processing- snRNAs participate in splicing and processing of RNAs.

24. References:
1. Google for images,
2. The selfish Genes- Richard Dawkins
3. Genome- Matt Ridley
4. Different open sources of information of WebPages
5. Biochemistry- Lehninger
2. Bio-molecules & Cell Biology- Arun chandra Sahu,
3. A textbook of Botany (Vol. II) Ghosh, Bhattacharya, Hait
4. Fundamentals of Biochemistry- Jain, Jain, & Jain,
5.A Textbook of Genetics- Ajoy Paul
DISCLAIMER:
This presentation has been made to enrich open source of learning
without any financial interest. The presenter acknowledges Google for
images and other open sources of information to develop this PPT.

25. AWESOME ROAD NEEDS
EXPLORATION
THANKS FOR YOUR VISIT