introduction and classification of nucleic acid in detail

1. NUCLEIC ACID
-VINOD KUMAR
3RD YEAR B.PHARMACY

2. INTRODUCTION
 Nucleic acid, naturally occurring chemical compound that is
capable of being broken down to yield phosphoric acid,
sugars, and a mixture of organic bases (purines and
pyrimidines).
 Nucleic acids are the main information-carrying molecules of
the cell, and, by directing the process of protein synthesis,
they determine the inherited characteristics of every living
thing.
CLASSIFICATION
 The two main classes of nucleic acids are deoxyribonucleic
acid (DNA) and ribonucleic acid (RNA).
 DNA is the master blueprint for life and constitutes the genetic
material in all free-living organisms and most viruses.
 RNA is the genetic material of certain viruses, but it is also
found in all living cells, where it plays an important role in
certain processes such as the making of proteins.

3. STRUCTURE OF NUCLEI
ACID
 Nucleic acids are polynucleotides—that is, long chainlike molecules
composed of a series of nearly identical building blocks called nucleotides.
Each nucleotide consists of a nitrogen-containing aromatic base attached
to a pentose (five-carbon) sugar, which is in turn attached to
a phosphate group.
 Each nucleic acid contains four of five possible nitrogen
containing bases: adenine (A), guanine (G), cytosine (C), thymine (T),
and uracil (U). A and G are categorized as purines, and C, T, and U are
collectively called pyrimidines.
 All nucleic acids contain the bases A, C, and G; T, however, is found only in
DNA, while U is found in RNA.
 The pentose sugar in DNA (2′-deoxyribose) differs from the sugar in RNA
(ribose) by the absence of a hydroxyl group (―OH) on the 2′ carbon of the
sugar ring.
 Without an attached phosphate group, the sugar attached to one of the
bases is known as a nucleoside.
 The phosphate group connects successive sugar residues by bridging the
5′-hydroxyl group on one sugar to the 3′-hydroxyl group of the next sugar in
the chain. These nucleoside linkages are called phosphodiester bonds and
are the same in RNA and DNA.

4. PURINES STRUCTURE
 Purine is a heterocyclic aromatic organic compound that consists of a pyrimidine ring
fused to an imidazole ring. It is water-soluble. Purine also gives its name to the wider
class of molecules, purines, which include substituted purines and their tautomers.
They are the most widely occurring nitrogen-containing heterocycles in nature
BASIC STRUCTURE OF PURINES
A and G are categorized as purines

5. STRUCTURE OF
PYRIMIDINES
 Pyrimidine is an aromatic heterocyclic organic compound .
 The pyrimidine ring system has wide occurrence in nature as substituted and ring fused
compounds and derivatives, including nucleotides cytosine, thymine and uracil, thiamine (vitamin
B1) and alloxan
BASIC STRUCTURE OF PYRIMIDINE
C, T, and U are collectively called pyrimidines

6. FORMATION OF PHOSPHODIESTER
BONDS
 A covalent bond in RNA or DNA that holds a polynucleotide chain together
by joining a phosphate group at position 5 in the pentose sugar of one
nucleotide to the hydroxyl group at position 3 in the pentose sugar of the
next nucleotide. — called also phosphodiester linkage.

7. TYPES OF NUCLEI ACID
 The two main types of nucleic acids
are deoxyribonucleic acid (DNA)
and ribonucleic acid (RNA). DNA is the
genetic material found in all living organisms,
ranging from single-celled bacteria to
multicellular mammals. It is found in the
nucleus of eukaryotes and in the chloroplasts
and mitochondria.

8. DEOXYRIBONUCLEI ACID
 DNA is a polymer of the four nucleotides A, C, G, and T, which are
joined through a backbone of alternating phosphate and deoxyribose
Sugar residues.
 These nitrogen-containing bases occur in complementary pairs as
determined by their ability to form hydrogen bonds between them. A
always pairs with T through two hydrogen bonds, and G always pairs
with C through three hydrogen bonds.
 The spans of A:T and G:C hydrogen-bonded pairs are nearly
identical, allowing them to bridge the sugar-phosphate chains
uniformly.
 This structure, along with the molecule’s chemical stability, makes
DNA the ideal genetic material. The bonding between
complementary bases also provides a mechanism for the replication
of DNA and the transmission of genetic information.

9. STRUCTURE OF DNA
DNA structure, showing the nucleotide bases cytosine (C), thymine (T), adenine
(A), and guanine (G) linked to a backbone of alternating phosphate (P) and
deoxyribose sugar (S) groups. Two sugar-phosphate chains are paired through
hydrogen bonds between A and T and between G and C, thus forming the twin-
stranded double helix of the DNA molecule.

10. CHEMICAL STRUCTURE OF DNA
 In 1953 James D. Watson and Francis H.C. Crick proposed a three-
dimensional structure for DNA based on low-resolution X-ray
crystallographic data and on Erwin Chargaff’s observation that, in naturally
occurring DNA, the amount of T equals the amount of A and the amount of
G equals the amount of C.
 Watson and Crick, who shared a Nobel Prize in 1962 for their efforts,
postulated that two strands of polynucleotides coil around each other,
forming a double helix.
 The two strands, though identical, run in opposite directions as determined
by the orientation of the 5′ to 3′ phosphodiester bond. The sugar-phosphate
chains run along the outside of the helix, and the bases lie on the inside,
where they are linked to complementary bases on the other strand through
hydrogen bonds.
 The double helical structure of normal DNA takes a right-handed form called
the B-helix.
 The helix makes one complete turn approximately every 10 base pairs. B-
DNA has two principal grooves, a wide major groove and a narrow minor
groove.
 Many proteins interact in the space of the major groove, where they make
sequence-specific contacts with the bases. In addition, a few proteins are

11. CHEMICAL STRUCTURE

12. RIBONUCLEI ACID
 RNA, abbreviation
of ribonucleic acid, complex
compound of high molecular
weight that functions in
cellular protein synthesis and
replaces DNA (deoxyribonucl
eic acid) as a carrier
of genetic codes in
some viruses. RNA consists
of ribose nucleotides(nitroge
nous bases appended to a
ribose sugar) attached by
phosphodiester bonds,
forming strands of varying
lengths. The nitrogenous
bases in RNA
are adenine, guanine, cytosin
e, and uracil

13. Types of RNA
 Messenger RNA (mRNA)
 Transfer RNA (tRNA)
 Ribosomal RNA (rRNA)

14. Messenger RNA (mRNA)
 Messenger RNA (mRNA) is a single-stranded RNA molecule that
corresponds to the genetic sequence of a gene and is read by
the ribosome in the process of producing a protein.
 mRNA is created during the process of transcription, where
the enzyme RNA polymerase converts genes into primary transcript mRNA
(also known as pre-mRNA).
 This pre-mRNA usually still contains introns, regions that will not go on to
code for the final amino acid sequence. These are removed in the process
of RNA splicing, leaving only exons, regions that will encode the protein.
 This exon sequence constitutes mature mRNA.
 Mature mRNA is then read by the ribosome, and, utilising amino
acids carried by transfer RNA (tRNA), the ribosome creates the protein.
This process is known as translation. All of these processes form part of
the central dogma of molecular biology, which describes the flow of genetic
information in a biological system.
 mRNA genetic information is in the sequence of nucleotides, which are
arranged into codons consisting of three base pairs each. Each codon
codes for a specific amino acid, except the stop codons, which
terminate protein synthesis.

15. Synthesis of RNA

16. RIBOSOMAL RNA
 Ribosomal ribonucleic acid (rRNA) is a type of non-coding
RNA which is the primary component of ribosomes, essential
to all cells. rRNA is a ribozyme which carries out protein
synthesis in ribosomes.
 Ribosomal RNA is transcribed from ribosomal DNA (rDNA)
and then bound to ribosomal proteins to
form small and large ribosome subunits.
 rRNA is the physical and mechanical actor of the ribosome
that forces transfer RNA (tRNA) and messenger
RNA (mRNA) to process and translate the latter into proteins.
 Ribosomal RNA is the predominant form of RNA found in
most cells; it makes up about 80% of cellular RNA despite
never being translated into proteins itself.
 Ribosomes are composed of approximately 60% rRNA and
40% ribosomal proteins by mass

17. T RNA
 A transfer RNA molecule is used in translation and
consists of a single RNA strand that is only about 80
nucleotides long, containing an anticodon on the other
end; the anticodon base-pairs with a complementary
codon on mRNA and transfer RNA is an
adaptor molecule composed of RNA, typically 76 to
90 nucleotides in length,that serves as the physical
link between the mRNA and the amino acid sequence
of proteins. tRNA does this by carrying an amino acid
to the protein synthetic machinery of a cell (ribosome)
as directed by a 3-nucleotide sequence (codon) in
a messenger RNA (mRNA). As such, tRNAs are a
necessary component of translation, the biological
synthesis of new proteins in accordance with
the genetic code.

18. STRUCTURE OF t RNA
 The structure of tRNA can be decomposed into its primary structure, its secondary
structure (usually visualized as the cloverleaf structure), and its tertiary structure.
The tRNA structure consists of the following:
 A 5'-terminal phosphate group.
 The acceptor stem is a 7- to 9-base pair (bp) 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). In general, such 3'-terminal tRNA-like structures are referred to as 'genomic tags'.
The acceptor stem may contain non-Watson-Crick base pairs
 The CCA tail is a cytosine-cytosine-adenine sequence at the 3' end of the tRNA molecule. The
amino acid loaded onto the tRNA by aminoacyl tRNA synthetases, to form aminoacyl-tRNA, is
covalently bonded to the 3'-hydroxyl group on the CCA tail. This sequence is important for the
recognition of tRNA by enzymes and critical in translation.[In prokaryotes, the CCA sequence is
transcribed in some tRNA sequences. In most prokaryotic tRNAs and eukaryotic tRNAs, the CCA
sequence is added during processing and therefore does not appear in the tRNA gene.
 The D arm is a 4- to 6-bp stem ending in a loop that often contains dihydrouridine
 The anticodon arm is a 5-bp stem whose loop contains the anticodon. The tRNA 5'-to-3' primary
structure contains the anticodon but in reverse order, since 3'-to-5' directionality is required to read
the mRNA from 5'-to-3'.
 The T arm is a 4- to 5- bp stem containing the sequence TΨC where Ψ is pseudouridine, a
modified uridine
 Bases that have been modified, especially by methylation (e.g. tRNA (guanine-N7-)-
methyltransferase), occur in several positions throughout the tRNA. The first anticodon base, or
wobble-position, is sometimes modified to inosine (derived from adenine), queuosine (derived

19. Schematic representation of
tRNA