BY-UTTARAN
MODHUKALYA(57), PARVIZ
ISLAM(70) ,2nd SEM.

We are very much pleased to submit our seminar
topic on Structure of DNA for B.Sc. 2nd semester. We
sincerely thanks to our honorable principal Dr.
Prasanna Kr. Dutta to give us opportunity for
preparing the seminar topic and our Professors
Dr.Indira Baruah (HOD), Dr.Gayatri Agni Bora and
Dr.Bikramaditya Bakalial of Zoology department of
our college for guiding properly the same.
We are also thankful to our other respected teachers
of the department and our friends and parents for
supporting us and help to make the seminar on the
above topic.

 Introduction
 Discovery of DNA
 Chemical composition of DNA
 Phosphoric Acid
 Pentose Sugar
 Nitrogenous Base
 Structure of DNA formed by three
main components
 Position of DNA in the chromosome
 Arrangement of DNA duplex
 Double helical structure of DNA
 Conclusion
 Reference

DNA is the genetic materials of all organisms
which is present in chromosome bind with
histone protein. DNA has two polynucleotide
chain which form a helical structure. The main
chemical components of the DNA are
phosphoric acid, deoxyribose sugar and four
different types of nitrogenous bases. The
phosphoric acid bind with the sugar by ester
bond, sugar-base bond is glycosidic bond
and bases are bound by hydrogen bond.
These are the basic component that form the
complete DNA structure.

 F. Miesher separate
DNA from nucleus in
1869.In 1889
Altmann gives the
term nucleic acid.
Watson and Crick
proposed the
acceptable DNA
double helix model
that can explain the
specificity and
replicablity of the
gene.

 The
deoxyribonucleic
acid mainly
composed of three
components-
1.Phosphoric
acid(H3PO4)
2.Pentose sugar
and
3.Nitrogenous base
.

 It may occur also
phosphate and forms the
backbone of DNA
molecule along with
sugar molecule. It links
the nucleotide by joining
the deoxyribose sugar of
two adjacent nucleotide
with an ester phosphate
bond. This bond connect
3prime carbon in one
nucleotide with 5prime
carbon in next.

 Deoxyribose sugar is
the pentose sugar
bearing C5H10O4
chemical formula
.The structure of
pentose sugar is
pentagonal ring
where 3 prime and 5
prime carbon atom
attached to
phosphoric acid and
in 1 prime carbon
atom to the base .

 It is of two types -
1.Purine
2.Pyrimidine
1.Purine :- It
compose of Adenine
and Guanine with two
heterocyclic ring and
contain C,H,O and N
atoms .

 2.Pyrimidine :–
Mainly cytosine and
thymine are the
base present in
DNA with single
heterocyclic ring .

In case of DNA the ribose sugar’s 1prime C join to the
base through glycosidic bond and this compound is
known as nucleoside .When the 5prime C is joined with
phosphoric acid by ester bond then the whole compound
is known as nucleotide. The deoxyribonucleotide joined
by phosphodiester bond and form a strand .Since DNA is
double helix so, It has two strand .The another strand
run in opposite or antiparallel direction i.e. if one strand
is 3 prime to 5prime end forward direction then the
another one is 5 prime to 3 prime end in backward
direction. The two strand is joined by hydrogen bond
between two nitrogenous base. The adenine always
forms two numbers of bond with thymine and cytosine
forms three bond with guanine base.

NUCLEOSIDE NUCLEOTIDE

 The diameter of DNA
is 20Ǻ. Distance of
major groove is 22Ǻ
and minor groove is
12Ǻ. The distance of
two base pair is 3.4Ǻ.
The diameter of
pyrimidine base is
3.3Ǻ and purine is
4.7Ǻ.

 From the above discussion we can
concluded that DNA has the double
helix that having two polynucleotide
chain coiled with each other .We
discuss about B-form DNA in the
above topic .

1. Textbook of medical biochemistry
2. A K Berry
3. Trueman elementary biology
4. Internet