RNA STRUCTURE, FUNCTION AND TYPES. . pptx

RNA STRUCTURE,
FUNCTION AND TYPES

• RNA is a single stranded polymer of ribonucleotides.
• It occurs in viruses, prokaryotic cells and Eukaryotic cells. It is largely
found in cytoplasm.
• It forms the major constituent of ribosome.

• RNA forms in the nucleolus, and then moves to specialized regions of
the cytoplasm depending on the type of RNA formed.
• RNA, containing a ribose sugar, is more reactive than DNA and is not
stable in alkaline conditions. RNA’s larger helical grooves mean it is
more easily subject to attack by enzymes.
• RNA strands are continually made, broken down and reused, and more
resistant to damage from UV light than DNA.

• RNA’s mutation rate is relatively higher, Unusual bases may be
present.
• The number of RNA may differ from cell to cell.
• Rate of renaturation after melting is quick.
• RNA is more versatile than DNA, capable of performing numerous,
diverse tasks in an organism.
• It is a polymeric molecule essential in various biological roles in
coding, decoding, regulation, and expression of genes

Chemical Composition
• Chemically RNA is made up of Ribose sugar, Phosphate and
nitrogenous bases like Adenine, guanine, cytosine and Uracil. In RNA,
thymine is absent.

Nucleosides
• Nucleosides of RNA RNA has 4 types of nucleosides, they are
(a) Ribose adenosine (b) Ribose guanosine (c) Ribose cytidine and
d) Ribose Uridine.
Ribose sugar + Adenine =Riboseadenosine
Ribose sugar + Guanine =Riboseguanosine.
Ribose sugar + Cytogine = Riboge cytidine.
Ribose sugar + uracil = Ribose uridine.

Nucleotides
• Nucleotides of RNA are Called Ribonucleotides. RNA has four types
of nucleotides, they are (a) Ribose adenylic acid or Ribose adenosine
monophosphate (Amp) (b) Ribose guanylic acid or Ribose guanosine
manophosphate (Gmp) (e) Ribose cytidylic acid or Riboge cytidine
monophosphate (cmp)
• i) Ribose Sugar + Adenine + phosphate = Ribose adenylic acid.
• ii) Ribose Sugar + Guanine + phosphate = Ribose guanylic acid.
• iii) Ribose Sugar + cytodine + phosphate = Ribosecytidylic acid.
• iv) Ribose Sugar + Uracil + phosphate = RiboseUridylic acid.

Salient features of RNA
• Genetic RNA and non-genetic RNA Genetic RNA : The RNA that
carry genetic or heredity character & from generation to generation is
called genetic RNA. Eg: RNA in Tmv (Tobacco mosaic virus), HIV,
Influenza virus, polio virus etc... Non genetic RNA: It is RNA does
not carry genetic character from generation to generation but helps in
protein synthesis.
• Based on the structure and function, Genetic RNAS are classified into
3 types. They are (1) mRNA (messenger RNA) (2) rRNA (ribosomal
RNA) (3) tRNA (transfer RNA).

• Like DNA, RNA is a long polymer consisting of nucleotides.
• RNA is a single-stranded helix.
• The strand has a 5′end (with a phosphate group) and a 3′end (with a hydroxyl
group).
• It is composed of ribonucleotides.
• The ribonucleotides are linked together by 3′ – 5′ phosphodiester bonds.
• The nitrogenous bases that compose the ribonucleotides include adenine,
cytosine, uracil, and guanine. Thus, the difference in the structure of RNA
from that of DNA include:
• The bases in RNA are adenine (A), guanine (G), uracil (U) and cytosine (C)

• Thus thymine in DNA is replaced by uracil in RNA, a different
pyrimidine. However, like thymine, uracil can form base pairs with
adenine.
• The sugar in RNA is ribose rather than deoxyribose as in DNA.
• The corresponding ribonucleosides are adenosine, guanosine, cytidine
and uridine. The corresponding ribonucleotides are adenosine 5’-
triphosphate (ATP), guanosine 5’-triphosphate (GTP), cytidine 5’-
triphosphate (CTP) and uridine 5’-triphosphate (UTP).

Messenger RNA (mRNA)
• mRNA (Messenger RNA) mRNA was discovered by VOLKIN in the
term mRNA was Coined by Jacob and Monad.

Characters of mRNA
• It is a linear single stranded polynucleotide chain. It forms about 3 to
5% of the total RNA content. It consists of about 900 to 1500
nucleotides. It has blue print or genetic message for protein synthesis.
It has no base pairing. Eukaryotic mRNA has a cap structure at s' end
which is a 7 methyl Guanosine nucleotide. Cap is absent in
prokaryotic RNA.

Structure
• mRNA a linear molecule consists of about 900-1500 ribonucleotides.
It has a cap structure at 5¹ end which is a 7' methyl guanosine
nucleotide. The cap is followed by the non coding region called leader
Sequence. The leader sequence is followed by Coding an initiator
codon AUG. It is followed by the coding or sensible region. The triplet
codons present in this region Code for aminoacids. The coding region
followed by the terminator Codons UAA, UAG or UGA. The coding
region followed by the non-coding region. It is followed by the poly A
tail 5 (polyadenylate tail) which forms 3' end of the of mRNA, Present
in Eukaryotic mRNA but absent in prokaryotic mRNA

FUNCTION
• mRNA Carry the genetic information from the DNA in the form
codons to the cytoplasm to synthesis protein at the ribosome.

TRANSFER RNA (tRNA)
• The RNA Carrying aminoacids to the ribosome for protein Synthesis
is called tRNA.
Characters
• It forms about 3 to 15% of the total RNA content. It is shortest RNA
consists of about 80 ribonucleotides. tRNA folded itself to produce
double stranded regions. The folded regions have base pairing i.e.,
A=U and C= G. It is also known as Soluble RNA (S RNA) or Adaptor
RNA

STRUCTURE
• Robert Holley was proposed Clover leaf model to explain the structure
of tRNA. (The folded tRNA appear like clover leaf (Trifolium).

• The tRNA shows the following structure.
• The t RNA has two ends, 3'end and 5'end. The 3'end has the base
Sequence 'CCA' and 5'end has GUA nucleotide.
• It has four arms. They named as Acceptor arm, Pseudouridine arm (Tψc
arm) DHU arm (Dihydrouxidine arm) and Anticodon arm.
• Each arm has two parts namely stem and loop, but acceptor arm hat only
stem. Acceptor arm has amino acid binding site 1.e., CCA to which amino
acid is attached. It consists of 3 unpaired and 7 paired nitrogenous bases.
• DHU arm 4 paired and 10 unpaired nitrogenous bases. It is meant for
attachment tRNA synthetase during protein Synthesis.

• TψC arm has 5 paired and 4 unpaired nitrogenous bases. It is meant
for attachment to a ribosome during protein Synthesis.
• Anti codon arm have 5 paired and 7 unpaired nitrogenous bases of
these three unpaired nitrogenous bases forms anticodon or NODOC. It
is Complementary to codon on mRNA.

Function
• tRNA transfer amino acid to ribosome (site of protein synthesis)
during protein synthesis. Transfer RNA brings or transfers amino acids
to the ribosome that corresponds to each threenucleotide codon of
rRNA. The amino acids then can be joined together and processed to
make polypeptides and proteins

• It is most abundantly (largely) occurring RNA in the cell. it forms about
80% of the total RNA content. It forms major component of ribosome. it
has many folded regions, folded regions have base pairing i e, A=U &
C≡ G. It consists of 120 to 4500 ribonucleotides. It is also known as
Structural RNA.
• It is a RNA forms the structural Component of the ribosome. Ribosomes
consist of two major components: the small ribosomal subunits, which
read the RNA, and the large subunits, which join amino acids to form a
polypeptide chain. Each subunit comprises one or more ribosomal RNA
(rRNA) molecules and a variety of ribosomal proteins (r-protein or
rProtein).

• Different rRNAs present in the ribosomes include small rRNAs and
large rRNAs, which denote their presence in the small and large
subunits of the ribosome.
• rRNAs combine with proteins in the cytoplasm to form ribosomes,
which act as the site of protein synthesis and has the enzymes needed
for the process.
• These complex structures travel along the mRNA molecule during
translation and facilitate the assembly of amino acids to form a
polypeptide chain. They bind to tRNAs and other molecules that are
crucial for protein synthesis

Functions
• It helps to form the structure of ribosome and helps to bind the mRNA
and tRNA to ribosome and rRNA directs the translation of mRNA into
proteins.

RNA STRUCTURE, FUNCTION AND TYPES. . pptx

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RNA STRUCTURE, FUNCTION AND TYPES. . pptx