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NUCLEIC ACID
 RNA
DNA
RNA
RNA
( RIBONUCLEIC ACID )
 SINGLE STRANDED NUCLEIC ACID.
 RNA CONTAINS RIBOSE (HYDROXYL
GROUP ATTACHED TO THE PENTOSE
RING) .
 UNSTABLE GENETIC MATERIAL W.R.T
DNA.
 COMPLEMENTARY BASE TO ADENINE IS
NOT THYMINE AS IT IS IN DNA BUT
URACIL.
DIFFERENCE BETWEEN
DNA & RNA
 DNA
 Double stranded helical
nucleic acid.
 Complementary base
to adenine is thymine.
 DNA contains
deoxyribose ( no
hydroxyl group
attached to the pentose
ring in the 2` position).
RNA
 Single stranded nucleic
acid.
 Complementary base
to adenine is uracil.
 RNA contain ribose i.e
hydroxyl group
attached to the
pentose ring in the 2`
position.
DNA
RNA
STRUCTURE OF RNA
 RNA is a ubiquitous family of macromolecule that perform
major vital role in the coding, decoding, regulation and
expression of genes. RNA is assembled as a chain of
nucleotides. Viruses encode their genetic material using an
RNA genome. RNA is a single stranded chain of nucleotide
comprise of sugar- phosphate backbone and four nitrogenous
base pairs (i.e adenine, uracil, guanine & cytosine) . RNA
contains ribose sugar. A phosphate group is attached to the
3` position of one ribose and 5` position of next. Bases form
hydrogen bonds b/w C-G & A-U. Structural feature of RNA
that distinguish it from DNA is the presence of a hydroxyl
group at the 2` position of ribose sugar. RNA is unstable in
nature due to 2` OH group, presence of uracil and its
TYPES OF RNA
 mRNA ( messenger RNA).
 rRNA






( ribosomal RNA ).
tRNA ( transfer RNA ).
tmRNA ( transfer messenger RNA).
snRNA or introns ( small nuclear RNAs).
PiRNA ( piwi-interacting RNAs).
dsRNA ( double stranded RNA).
tasiRNA ( trans-acting siRNA).
LIST OF RNAs IN NATURE
TYPE
 mRNA
 rRNA
 tRNA
 snoRNA
 FUNCTION
 Codes for protein.
 structural & catalytic
role during translation.
 translation. (brings
aminoacids & reads the
genetic code).
 Nucleotide modification
of RNAs.
LIST OF RNA
TYPES




Sm Y RNA
snRNA
SRP RNA
Rnase MRP
FUNCTION
 mRNA trans – splicing.
 splicing & other function.
 membrane integration.
 rRNA maturation & DNA
replication.




Telomerase RNA
miRNA
piRNA
Satellite RNA
 telomere synthesis.
 gene regulation.
 transposon defence.
 self propogating.
mRNA
mRNA CODON CHART
mRNA
PROCESSING
Messenger RNA is a large family of
RNA molecule that convey genetic
information from DNA to the ribosome
, where they specify the amino acid
sequence of the protein products of
gene expression . Following
transcription of mRNA by RNA
polymerase , the mRNA is translated into
a polymer of amino acid . mRNA genetic
information is encoded in the sequence
of nucleotides , which are arranged into
codons consisting of three bases.
Each codon encodes for a specific
amino acid , except the stop
codons which terminate the protein
synthesis .This process of
translation of codon into amino
acids requires two other types of
RNA : tRNA that mediates
recognition of codon & provides the
corresponding amino acid and
rRNA that is central component of
the ribosomes protein –
manufacturing machinery .
During transcription,RNA polymerase makes a copy
of a gene from the DNA to mRNA as needed.The
short lived unprocessed product is termed
precursor mRNA.Eukaryotic pre mRNA requires
extensive processing.
5' cap addition :
A 5' cap (also termed an RNA cap, an RNA 7methylguanosine cap) is a modified guanine
nucleotide that has been added to the "front" or
5' end of a mRNA after the start of
transcription. The 5' cap consists of a terminal
7-methylguanosine residue.Shortly after the
start of transcription, the 5' end of the mRNA
being synthesized is bound by a cap-synthesizing
complex associated with RNA polymerase. This
enzymatic complex catalyzes the chemical
reactions that are required for mRNA capping.
Splicing is the process by which premRNA is modified to remove certain
stretches of non –coding sequences
called introns ; the stretches that
remain include protein -coding
sequences and are called exons .
Sometimes pre -mRNA messages may be
spliced in several different ways ,
allowing a single gene to encode
multiple proteins . This process is called
alternative splicing . Splicing is usually
performed by an RNA -protein complex
called the spliceosome , but some RNA
molecules are also capable of
catalyzing their own splicing ( see
ribozymes ).
Polyadenylation is the covalent linkage
of a polyadenylyl moiety to a messenger
RNA molecule. In eukaryotic organisms
, with the exception of histones , all
messenger RNA (mRNA) molecules are
polyadenylated at the 3' end . The poly
(A) tail and the protein bound to it aid
in protecting mRNA from degradation by
exonucleases . Polyadenylation is also
important for transcription termination .
RIBOSOMAL RNA
Ribosomal ribonucleic acid (rRNA) is
the RNA component of the ribosome,
and is essential for protein synthesis in
all living organisms. It composes the
predominant material within the
ribosome, which is ca. 60% rRNA and
40% protein by weight. Ribosomes
contain two major rRNAs and 50 or
more proteins.The LSU rRNA acts as a
ribozyme, catalyzing peptide bond
formation. The ribosomal RNAs form
two subunits, the large subunit (LSU)
and small subunit (SSU).
mRNA is sandwiched between the small and
large subunits, and the ribosome catalyzes
the formation of a peptide bond between the
2 amino acids. A ribosome also has 3 binding
sites called A, P, and E. The A site in the
ribosome binds to an aminoacyl-tRNA (a
tRNA bound to an amino acid).
The amino (NH2) group of the aminoacyl-tRNA,
which contains the new amino acid, attacks the
ester linkage of peptidyl-tRNA (contained within
the P site), which contains the last amino acid
of the growing chain, forming a new peptide
bond. This reaction is catalyzed by peptidyl
transferase . prokaryotic and eukaryotic
ribosomes can be broken down into two subunits
(the S in 16S represents Svedberg units), nt=
length in nucleotides of the respective rRNAs.
Prokaryotic = Both 70S
50S (5S : 120 nt, 23S : 2906 nt)
30S (16S : 1542 nt)
eukaryotic = 80S
60S (5S : 121 nt,[1] 5.8S : 156 nt,[2] 28S : 5070)
40S (18S : 1869 nt)
Eukaryotes generally have many copies of the
rRNA genes organized in tandem repeats; in
humans approximately 300–400 repeats are
present in five clusters (on chromosomes 13,
14, 15, 21 and 22). Because of their special
structure and transcription behaviour, rRNA
gene clusters are commonly called "ribosomal
DNA”.
The 18S rRNA in most eukaryotes is in the
small ribosomal subunit, and the large
subunit contains three rRNA species (the 5S,
5.8S and 28S in mammals, 25S in plants,
rRNAs).
Mammalian cells have 2 mitochondrial (12S
and 16S) rRNA molecules and 4 types of
cytoplasmic rRNA (the 28S, 5.8S, 18S, and 5S
subunits). The 28S, 5.8S, and 18S rRNAs are
encoded by a single transcription unit (45S)
separated by 2 internally transcribed spacers.
The 45S rDNA organized into 5 clusters (each
has 30-40 repeats) on chromosomes 13, 14,
15, 21, and 22. These are transcribed by RNA
polymerase I.
Translation is the net effect of proteins being
synthesized by ribosomes, from a copy (mRNA)
of the DNA template in the nucleus.
TRANSFER RNA
A tRNA is an adaptor molecule composed
of RNA, typically 73 to 94 nucleotides in
length, that serves as the physical link
between the nucleotide sequence of
nucleic acids (DNA and RNA) and the amino
acid sequence of proteins . It does this by
carrying an amino acid to the protein
synthetic machinery of a cell (ribosome) as
directed by a three –nucleotide sequence
(codon) in a messenger RNA (mRNA) . As
such , tRNAs are a necessary component of
protein translation , the biological synthesis
of new proteins according to the genetic
code .
The specific nucleotide sequence of
an mRNA specifies which amino
acids are incorporated into the protein
product of the gene from which the
mRNA is transcribed , and the role of
t RNA is to specify which sequence
from the genetic code corresponds to
which amino acid . One end of the
tRNA matches the genetic code in a
three- nucleotide sequence called the
anticodon . The anticodon forms three
base pairs with a codon in mRNA
during protein biosynthesis .
The covalent attachment to the tRNA 3’ end is
catalyzed by enzymes called aminoacyl-tRNA
synthetases . During protein synthesis , tRNAs
with attached amino acids are delivered to the
ribosome by proteins called elongation factors
which aid in decoding the mRNA codon
sequence .
If the tRNA 's anticodon matches the mRNA ,
another tRNA already bound to the ribosome
transfers the growing polypeptide chain from its
3 ’ end to the amino acid attached to the 3 ’ end
of the newly delivered tRNA , a reaction
catalyzed by the ribosome.
The cloverleaf structure becomes the 3D L-shaped
structure through coaxial stacking of the helices, which
is a common RNA Tertiary Structure motif. The 5'terminal phosphate group. The acceptor stem is a 7base pair stem made by the base pairing of the 5'terminal nucleotide with the 3'-terminal nucleotide
(which contains the CCA 3'-terminal group used to
attach the amino acid). The CCA tail is a cytosinecytosine-adenine sequence at the 3' end of the tRNA
molecule. This sequence is important for the recognition
of tRNA by enzymes and critical in translation. The D
arm is a 4 bp stem ending in a loop that often contains
dihydrouridine. The anticodon arm is a 5-bp stem
whose loop contains the anticodon. The T arm is a 5 bp
stem containing the sequence TΨC where Ψ is a
pseudouridine.
An anticodon is a unit made up of three nucleotides that
correspond to the three bases of the codon on the mRNA.
Each tRNA contains a specific anticodon triplet sequence
that can base -pair to one or more codons for an amino
acid . Some anticodons can pair with more than one codon
due to a phenomenon known as wobble base pairing . To
provide a one –to -one correspondence between tRNA
molecules and codons that specify amino acids , 61 types of
tRNA molecules would be required per cell .
Aminoacylation is the process of adding an aminoacyl
group to a compound . It produces tRNA molecules with
their CCA 3‘ ends covalently linked to an amino acid . Each
tRNA is aminoacylated (or charged ) with a specific amino
acid by an aminoacyl tRNA synthetase . There is normally a
single aminoacyl tRNA synthetase for each amino acid .
FUNCTION OF mRNA
 IT CONVEY GENETIC INFORMATION FROM
DNA TO THE RIBOSOMES , WHERE THEY
SPECIFY THE AMINO ACIDS SEQUENCES OF
PROTEINS PRODUCTS OF GENE
EXPRESSION.FOLLOWING TRANSCRIPTION
OF mrna BY RNA POLYMERASE , THE mRNA
IS TRANSLATED INTO A POLYMER OF AMINO
ACID.INFORMATION IN DNA CANNOT BE
DIRECTLY DECODED INTO PROTEINS, IT IS
FIRST TRANSCRIBED OR COPIED INTO mRNA.
FUNCTION OF tRNA
 TRANSFER RNA FUNCTION AS AN
INTERPRETER BETWEEN NUCLEIC ACID &
PROTEIN LANGUAGE BY PICKING UP
SPECIFIC AMINO ACIDS AND
RECOGNIZING THE APPROPRIATE CODON
IN THE MRNA .ITS MAIN FUNCTION IS TO
TRANSFER AMINO ACIDS TO GROWING
POLYPEPTIDE CHAIN DURING THE
RIBOSOMAL SITE OF PROTEIN SYNTHESIS
DURING TRANSLATION.
FUNCTION OF rRNA
 RIBOSOMAL RNA FORMS PART OF RNA ,WHICH ARE
INVOLVED IN PROTEIN SYNTHESIS.THE CATALYTIC
ACTIVITY OF THE RIBOSOME -THE CREATION OF A
CHEMICAL BOND BETWEEN TWO AMINO ACIDS I.E
PEPTIDE BOND COMES FROM THE RNA COMPONENT OF
RIBOSOME.