Nucleic Acids
Bio-molecules

are compounds composed of repeating
units of their building blocks i.e.
monomers.

There are four major classes of biomolecules found in the cells and tissues,
among them include; lipids, polysaccharide,
proteins and nucleic acids.
Nucleic acids

are high molecular compounds composed of
mono-nucleotides linked to chains by 3`, 5`
phosphodiester linkages.
Nucleic acids are of 2 types:
1. DNA (the building blocks of DNA are
deoxyribonucleotides).
2. RNA (the building blocks of RNA are
ribonucleotides).
Nucleotides
are compounds consisting of a nucleoside
combined with a phosphate group and forming
the basic constituent (building blocks) of DNA
and RNA.
 In other word, nucleotides are made up of a
nitrogenous base, a pentose sugar (a five carbon
sugar) and a phosphate group.

The nucleotides are of 2 types:
1. Ribonucleotide, which contain ribose.
2. Deoxyribonucleotide, which contain 2`
deoxyribose.

Nucleosides
are compounds consisting of nitrogenous bases
(purine or pyrimidine) linked to pentose sugar
usually ribose or deoxyribose by N-glycosidic
linkages.
 The nucleosides are N-glycosides in which the
sugar C1 atom is linked to the N9 of purine, or
to the N1 of pyrimidine.
 There are 2 different types of nucleosides:
1. deoxyribonucleosides containing 2deoxyribose and
2. ribonucleosides containing ribose.

Pentose sugar
Structure of nucleotides
N-bases
nitrogenous bases of nucleic acids are of 2
types:
 Purine bases.
 Pyrimidine bases.
 Major purine bases are Adinine (A), and
Guanine (G).
 Major pyrimidine bases are Cytosine (C),
Uracil (U) and Thymine (T).
 DNA contains: A, G, C and T. Whereas RNA
contains A, G, C and U

GENERAL
CHARACTERIZATION OF
NUCLEIC ACIDS
CONCENTRATIO
N

Varies depending upon the functional state of the
cells. Ex. spermatozoa: DNA 60%, muscle cells: DNA
0.2%. DNA is present in high conc. where there is
high protein synthesis on dry matter basis.
LOCATION

DNA
 Prokaryotes: DNA located in the special region of
the cytoplasm, nucleoid or bound to the bacterial
membrane. A small position of DNA is located in
plasmids.
 Eukaryotes: DNA is distributed between the
nucleus 97-99% (where it forms part of
chromosomes and nucleolus) and extra nuclear
organelles (mitochondria).

•
RNA
Distributed uniformly over the cell. Hence distribution
indicates that function is more dynamic & extensive.
Molecular mass
• DNA, Varies with biological complexity at the cell.
• RNA less than DNA
Structure and Level of
Organization of Nucleic Acid

Nucleic acids posses' primary, secondary and
tertiary levels of organization.

DNA because of it is high molecular mass
posses all the 3 regular structures, whereas
RNA does not exhibit regular 1, 2, 3 structures.
Primary structure

Of DNA & RNA is a linear polynucleotide
chain made up of mononucleotides, linked
together by 3`, 5`phosphodiester linkages.

The buildup of both DNA & RNA primary
structures follows the same principle.
I.e. each pentose 3`-OH group of MNP is linked
covalently to pentose 5`-OH group of the
neighboring, MNP. Hence the name derived as
3`, 5` phosphdiester linkage.
Linear chains of DNA & RNA, hence have 2 ends called as
3` (3 prime) and the 5` (5 prime) end.
 The 5` end always containing phosphate group (NTP) and
3` end, contain a hydroxyl group (OH group). Thus the
chains are polar and directed either
5`  3` or 3` 5`.


The genetic text of DNA composed of code words called
codons, or code triplets, which are linear sequences of 3
adjacent nucleotides.

The sites of DNA chain containing information on the
primary structure of RNA(s) are refer as Structural Genes.
The ordering of nucleotides in RNA is the same as in the
DNA region i.e. being replicated.
THE PRIMARY STRUCTURE DETERMINES HIGHER LEVELS
(SECONDARY & TERTIARY) OF THE NUCLEIC ACID
ORGANIZATION.
NOTE: IF STRUCTURAL GENE – STRUCTURAL PROTEIN.
IF REGULAR GENE – REGULAR PROTEIN.
Secondary and Tertiary
structures of DNA

Chargaff (1949) established a number of
important relationships concerning the
contents of individual bases in DNA these
relationships help us in classifying the sec.
structure of DNA.
Chargaff Rule
1. Total number of purine (A+G) is equal to total
number of pyrimidine (C+T).
I.e. A + G / C + T = 1
2. A = T or A/T = 1.
3.G = C or G/C =1.
4.The numbers of (A + T) and (G + C) are only
variables, i.e. A + T ± G + C.
■If (A + T) > (G + C) then DNA is
referred as (AT- type).
■If (G + C) > (A + T) then DNA is
referred as (GC- type).
WATSON AND CRICK FINALLY PROPOSED DNA AS A
DOUBLE HELIX STRUCTURE
(SECONDARY STRUCTURE)
Characterization of DNA double
helix
The DNA double helix is formed via a special paring
of a base of one polypeptide chain with a base of
the other polypeptide chain, A with T, and G with C.
 The first pairing through 2-H bonds and the second
pairing through 3-H bonding.
i.e. A = T , C = G.
 Such a much correspondence is called as
complimentary. Due to their complementary, the
two chains run opposite to one another,
i.e. antiparallel.
 One in 5`  3`, the other in 3` 5` direction..

DNA secondary structure
The sugar-POA is directed outwards, where as base
pairing protrudes into the interior of the helix.
One full turn of helix contains 10 nucleotides.
In native chromosomal DNA, the double helix deviates
from the perfect pattern in the chain regions referred
as Palindrome.
In palindromes the ordering of nucleotides along the
chain from right to left and from left to right is the
same (repetitive, non informative segments).
for example
5' A C C T A G G T 3'
3' T G G A T C C A 5'
Tertiary structure of
DNA (super coiling)
Twisted double helical
structure in space is
known as tertiary
structure.