The document discusses the structure and types of ribonucleic acid (RNA). It notes that RNA is a polymer of ribonucleotides found in all living cells and viruses. There are various types of RNA including messenger RNA (mRNA), transfer RNA (tRNA), ribosomal RNA (rRNA), and micro RNA (miRNA). mRNA encodes proteins, tRNA transfers amino acids during protein synthesis, rRNA is a major component of ribosomes, and miRNA regulates gene expression post-transcriptionally. The document provides details on the chemical composition, functions, and synthesis of these different RNA types.

1. STRUCTURE OF NUCLEIC ACID :
RIBONUCLEIC ACID (RNA )
rRNA,mRNA,tRNA and Micro RNA
BY
Dr. Ichha Purak
University Professor
Ranchi Women’s College,Ranchi
http://www.dripurak.com/
http://drichhapurak.webnode.com/

2. Friedrich Miescher in 1869 discovered substance
nuclein from the nuclei of pus cells which was later
termed nucleic acid because of having phosphate
group and was of acidic nature.
Nucleic acids are present in all living organisms
(plants,animal,bacteria and even Virus and viriods)
and therefore origin of life is suspected with the
formation of nucleic acids. All living cells contain
both DNA and RNA, while viruses contain either DNA
or RNA, usually not both.
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3. The nucleic acids are most important
biological macromolecules responsible for transmission and
storage of heredity or genetic information from one generation
to next by means of Replication, Transcription and Translation.
Nucleic acids are fibre like molecules having much greater
length in comparision to diameter
Nucleic acids are the found in abundance in all living things,
where they function in encoding, transmitting and expressing
genetic information
The nucleic acids are generally associated with proteins to
form nucleoproteins
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4. There are two types of nucleic acids :
RNA (Ribonucleic acid ) = (Ribonucleotide )n –A U C G
DNA ( Deoxyribonucleic acid)=(Deoxyribonucleotide)n
– A T C G
These are polymers consisting of long chains of monomers
called nucleotides linked in a chain through
phosphodiester bond
A nucleotide consists of a nitrogenous base, a pentose sugar
and a phosphate group
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5.  There are two related pentose sugars:
- RNA contains ribose
- DNA contains deoxyribose
 The sugars have their carbon atoms numbered with
primes to distinguish them from the nitrogen bases
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6. NITROGEN BASES
 The nitrogen bases in nucleotides consist of two general types:
 - pyrimidines: cytosine (C), thymine (T) and Uracil (U)
 - purines: adenine (A) and guanine (G)
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7.  The primary structure of a nucleic acid
 is the nucleotide sequence joined by phosphodiester bonds
 The 3’-OH group of the sugar in one nucleotide forms an ester bond
to the phosphate group on the 5’-carbon of the sugar of the next
nucleotide
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8. READING PRIMARY STRUCTURE
 A nucleic acid polymer has a
free 5’-phosphate group at one
end and a free 3’-OH group at
the other end
 The sequence is read from the
free 5’-end using the letters of
the bases
 This example reads
5’—A—C—G—T—3’
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9. EXAMPLE OF RNA PRIMARY STRUCTURE
In RNA, A, C, G, and U are linked by 3’-5’ ester bonds between
ribose and phosphate
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10. RNA is polymer of
Ribonucleotides
RNA is a polymeric
constituent of all living
cells and many viruses. it is
long single stranded chain
of alternating phosphate
and ribose sugar units with
the nitrogenous bases
Adenine & guanine
(purines) and cytosine and
uracil (pyrimidines) bonded
to ribose sugar.
RIBONUCLEIC ACID (RNA )
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11. Chemical structure of RNA
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12. RBONUCLEOTIDES
(AMP )adenosine
monophosphate
(GMP) gwanosine
monophosphate
PURINES
(CMP) cytidine
monophosphate
(UMP) uridine
monophosphate
PYRIMIDINES

13. 13
STRUCTURE OF RIBO NUCLIC ACIDS
 Polymers of four nucleotides
 Linked by alternating sugar-phosphate bonds
 RNA: ribose and A, C, G, U
P sugar
A
P sugar
G
P sugar
C
P sugar
U
AMP
CMP
GMP
UMP

14. RNAs are usually single
stranded, but many RNA
molecules have secondary
structure in which
intramolecular loops are formed
by complementary base pairing
(tRNA and rRNA ).
Base pairing in RNA follows
exactly the same principles as
with DNA: the two regions
involved in duplex formation are
antiparallel to one another, and
the base pairs that form are A-U
and C-G
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15. RNA is much more abundant than DNA
DFFERENCES BETWEEN RNA AND DNA
S N RNA DNA
1 RNA is polymer of Ribonucleotides DNA is polymer of
Deoxyribonucleotides
2 RNA has Ribose sugar DNA has Deoxyribose sugar
3 Ribose sugar (C5H10O5) has OH-
at C2,C3 &C5
Deoxyribose Sugar has OH- only at
C3 & C5
4 RNA is generally single stranded
Exception tRNA & rRNA at some
places are double stranded
DNA is Generally Double Stranded
Exception In Bacteriophage Ф-
174 and S-13
5 RNA has Pyrimidines Cytosine
and Uracil
DNA has Pyrimidines Cytosine
and Thymine
6 RNA generally Non Genetic but
in some Viruses it is Genetic
Material
DNA is Genetic Material
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16. 7 RNA is not stable DNA is stable in alkaline
condition
8 RNA is synthesized by
transcription using one strand
of DNA as Template
DNA is Synthesized by
Replication using both
strands of DNA as templates
during Interphase
9 In helical regions A-U and C-G
are the Base Pairs
A- T and C-G are the Base
Pairs
10 The helix geometry of RNA is
of A-Form
Is destroyed by enzymes and
produced again
The helix geometry of DNA is
of B-Form
Protects itself against
enzymes
11 RNA performs the function of
a messenger between DNA
and the proteins.
DNA performs long term
storage and transfer of
Genetic Information
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17. Ribose replaces deoxyribose; uracil replaces thymine
RNA
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18. S N Coding RNA Non-coding RNAs
1 mRNA (Messenger RNA)
2 tRNA ( Transfer RNA)
3 rRNA (Ribosomal RNA
4 snRNA (Small nuclear RNA )
5 snoRNA (Small nucleolar RNA )
6 scRNA (Small cytoplasmic RNA)
7 aRNA (Antisense RNA )
8 miRNA (microRNA )
9 siRNA (small interference RNA )
10 Ribozyme (catalytic RNA )
11 cRNA (Complementary RNA )
12 gRNA ( guide RNA )
TYPES OF RNAs
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19. MAJOR TYPES OF RNAS
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SYNTHESIS AND MAIN FUNCTIONS OF DIFFERENT RNAs

21. BRIEF DESCRIPTION OF DIFFERENT RNAS
Messenger RNA(mRNA )-is the only coding RNA as it
bears a complementary copy of deoxyribonucleotide
sequence present on Gene (DNA segment ) as
ribonucleotide sequence. It encodes chemical blueprint
for protein synthesis in 5’-3’ direction. It is single
stranded
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22. Transfer RNA (tRNA) is a small
RNA chain(73-95 nucleotides ) that
transfers a specific amino acid to a
growing polypeptide chain at
ribosome during translation.
It acts as a adapter molecule
because it can recognise both a
specific Amino Acid as well as its
codon on mRNA. For loading 20
different protein Amino Acids there
are different tRNAs.(1-20) Each amino
acid is recognized by one or more
specific tRNA
tRNA has a tertiary structure
that is L-shaped one end
attaches to the amino acid and
the other binds to the mRNA
by a 3-base complimentary
sequence Anticodon
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23. Ribosomal RNA(rRNA )
is the most stable RNA .It is
synthesized by Nucleolar genes
by RNA polymerase I and make
40-60% by weight of total RNA
and is 80% of total RNA of the
cell. It may measure upto 7000 Aᵒ
in extended form . It is main
component of ribosomes along
with proteins
Ribosomes are the sites of
protein synthesis ,consisting of
ribosomal RNA (65%) and
proteins (35%), have a small and
a large subunit
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24. Small nuclear RNA
(snRNA) a class of small
eukaryotic RNA molecules
found in the nucleus usually as
ribonucleoproteins which are
involved in processing
heterogenous nuclear
messenger RNA (Splicing of
Exons )U1, U2 U4, U5 and U6
and also used in RNA
interference
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25. Small nucleolar RNA (snoRNAs ) are a class of small RNA
molecules that guide chemical modification (methylation or
puedouridylation ) of ribosomal RNAs
Small cytoplasmic RNA (scRNA) small (7S,129
nucleotides) RNA found in cytosol and rough endoplasmic reticulum
associated with proteins ,component of SRP (Signal Recognition
Particle ) that are involved in specific selection and transport of
secretory proteins by recognizing signal sequence at amino terminus
of growing polypeptide chain.
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26. Signal Sequence directing Protein Targetting
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27. Antisense RNA (aRNA) is a single stranded RNA that is
complementary to a mRNA strand . Antisence mRNA (artificially
synthesized ) may be introduced into a cell to inhibit translation
of a complementary mRNA by base pairing to it and physically
obstructing (blocking) the translation machinery. It is thought as
promising technique for disease therapy.
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28. microRNAs (miRNA )
MicroRNAs were first described in 1993 by Rosalind Lee, Victor
Ambros, and Rhonda Feinbaum in the nematode Caenorhabditis elegans
MicroRNAs constitute a recently discovered class of non-coding RNAs
that play key roles in the regulation of gene expression by gene silencing
Mature microRNAs are short, single-stranded RNA molecules
having about 21- 23 nucleotides in length
The genes encoding miRNAs are much longer than the processed
mature miRNA molecule
MicroRNA genes are transcribed by RNA polymerase II as large
primary transcripts (pri-microRNA)
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29. Pri-microRNA has a cap and Poly-A tail before undergoing processing
like mRNA Pri-microRNAs are processed by a protein complex
Drosha containing RNase III enzyme to form an approximately 70
nucleotide precursor microRNA (pre-microRNA).
This molecule has stem-loop structure
This precursor is subsequently transported to the cytoplasm where it is
processed by a second RNase III enzyme, DICER, to form a mature
microRNA of approximately 22 nucleotides
This mature miRNA has some complementary sequences to one or more
mRNAs
The mature microRNA is then incorporated into a ribonuclear particle to
form the RNA-induced silencing complex, RISC, which mediates gene
silencing through RNA interference.
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30. MicroRNAs usually induce gene silencing by binding to target sites
found within the 3’UTR of the targeted mRNA.
This interaction prevents protein production by suppressing protein
synthesis by initiating mRNA degradation
Since most target sites on the mRNA have only partial base
complementarity with their corresponding microRNA, individual
microRNAs may target as many as 100 different mRNAs.
MicroRNAs play significant role in cell cycle control,apoptosis,stem cell
differentiation etc.MicroRNAs are also involved in tissue-specific
expression
MicroRNAs are a class of post-transcriptional regulators
They are short ~22 nucleotide RNA sequences that bind to
complementary sequences in the 3’ UTR of multiple target mRNAs,
usually resulting in their silencing.
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31. Processing of miRNA
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32. Function of Micro RNA ( MiRNA) Small but mighty
a microRNA (miRNA), silences genes
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33. Small interfering RNA ( siRNA ) is considered
exogenous double-stranded RNA that is taken up by cells, or
enters via vectors like viruses, while miRNA is single stranded and
comes from endogenous (made inside the cell) non-coding RNA,
found within the introns of larger RNA molecules.
siRNA are double stranded RNA fragments,which trigger
catalytically mediated gene silencing by targetting RNA Induced
Silencing Complex ( RISC) to bind and degrade the mRNA
Both siRNA and miRNA can play a role in epigenetics through a
process called RNA-induced transcriptional silencing (RITS).
Likewise, both are important targets for therapeutic use, because
of the roles they play in the controlling gene expression.
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34. Ribozyme ( Catalytic RNA ) is ribonucleic acid molecules
having catalytic activity as protein enzymes
Till 1989 it was believed that all enzymes are proteinaceous in
nature. During observing spilicing mechanism of Group I rRNA
intron from protozoa Tetrahymena thermophila by Thomas Cech and
Sydney Altman, it was realized that no proteins were involved in this
process. It was revealed that RNAs could also have catalytic
function. In this case the rRNA was processed for removal of intron
and spilicing exons without any intervention of any protein.
This post transcriptional processing of rRNA led to discovery of
RNA enzyme or RIbozyme or Non-protein enzymes.
Examples
RNase P
Group I and Group II introns
Peptidyl transferase 23S rRNA
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35. Splicing mechanism of Group I intron .The nucleophile in the
first step may be gwanosine,GMP,GDP or GTP

36. Guide RNA (gRNA) are RNA genes that function in RNA editing,
found in mitochondria by inserting or deleting stretches of
uridylates (Us) . The gRNA forms part of editosome and contain
sequences to hybridize to matching sequences in the mRNA to
guide the mRNA modifications.
Complementary RNA( cRNA ) viral RNA that is transcribed
from negative sense RNA and serves as a template for protein
synthesis
Negative sense RNA viral RNA with a base sequence complementary to
that of mRNA during replication it serves as a template to the
transcription of viral complementary RNA
Positive sense RNA viral RNA with same base sequence as mRNA
during replication function as mRNA ,serving as template for protein
synthesis
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37. RNA interference Experimental use by introducing small ds
RNAs for functional deactivation of specific genes ,which induces
degradation of complementary single stranded mRNA encoded by
the gene , gene silencing.
RNA interference is a related process in which double stranded
RNA fragnments called small interfering RNAs trigger catalytically
mediated gene silencing most typically by targeting the RNA
induced Silencing Complex (RISC) to bind to and degrade the mRNA
Attempts to genetically engineer transgenic plants to express
antisense RNA instead activate the RNA pathway, although the
processess result in differing magnitude of gene silencing.
Well known examples include Flavr Savr tomato and two cultivars of
ringspot papaya
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38. FUNCTIONS OF DIFFERENT RNA
mRNA – It carries genetic formation of DNA ( Gene ) for protein
synthesis from nucleus to ribosome in the form of genetic code
tRNA – Acts as adapter molecule ,carries Amino Acid and drops
it to particular location by recognising codon on mRNA by virtue
of having anticodon
rRNA – It makes complex with proteins and form ribosomal
subunits which provide space for protein synthesis ,single
ribosomal RNA of smaller subunit helps correct orientation of
mRNA during attachment with respect to P and A sites
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snRNA – play significat role in eukayotic mRNA processing
By splicing of exons as snRNPs or snurps U1,U2, U4,U5 &U6
scRNA – being component of Signal Recognition Particle (SRP )
helps in targetting of seceretary proteins
snoRNA – Plays role in gene silencing
miRNA – play important role in gene silencing by blocking mRNA
and preventing translation

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Si RNA – Plays important role in gene silencing by interfering
transcription
gRNA- help in RNA editing in mitochondria , forms part of
editosome and hybridize with matching sequence of mRNA
Catalytic RNA –Ribozymes act as protein enzymes in catalyzing
removal of intron, peptide bond formation etc
aRNA- antisense RNA - is artificially used to block translation of
perticular messenger RNAs so as to prevent formation of some
harmful proteins

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