The document discusses the structure of DNA as proposed by Watson and Crick in 1953. Some key points: - Watson and Crick discovered that DNA has a double helix structure with two polynucleotide strands coiled around each other. - The strands are anti-parallel, with nitrogenous bases projecting inward and forming hydrogen bonds between complementary base pairs of A-T and C-G. - Their model explained how DNA replicates - the two strands separate and each acts as a template for a new partner strand, ensuring the base pairings are preserved.

1. “Structure of DNA”

2. Review Literature
Occurrence of DNA
METHODOLOGY
What is DNA?
Chemistry of DNA
Model of DNA
Structure of DNA
Conclusion
Presentation
Outline

3. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
WHAT IS DNA?
 DNA is an important bio molecule which
transfer the genetic material from generation
to generation.
 DNA is responsible for all metabolic
activities inside the body and it is present
inside the body.
 The DNA is purely responsible for physical
appearance of the organism.
OCCURANCE:-
 It occurs inside each of the cells of the
organism.
Introduction

4. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
 Roselind Franklin discovered the double helical
structure of DNA by X-ray Crystallographic
studies.
 Watson and Crick discovered the double helical
model of DNA in 1953 and they share a noble
prize in 1962.
Model of DNA
1953 – Watson and Crick's 3D Model
of DNA

5. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
Chemistry of DNA
 The two strands of DNA are known as polynucleotide since they are simple units
called nucleotides.
 Deoxyribonucleic acid (DNA) is bound in nucleus and mainly in the
chromosomes.
 DNA consist of
(i) Nitrogenous Bases
(ii) Deoxyribose sugar or Pentose sugar
(iii) Phosphoric Acid
(i) Nitrogenous Bases:-
It mainly consist of purine and pyrimidine.
1. Purine:- It consist of Adenine and Guanine.
2. Pyrimidine:- It consist of Thymine and Cytosine
(ii) Deoxyribose sugar/Pentose sugar:-
The sugar present in DNA is deoxyribose type. So it is called pentose sugar.
(iii) Phosphoric acid :-
The phosphoric acid present is DNA phosphoric acid.

6. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
Chemistry of DNA

7. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
Structure of DNA
 The structure of DNA molecule was
proposed by James D. Watson and
H.C. Crick in 1953.
 For their work they were awarded
with Nobel Prize in year 1962.
 According to them DNA is composed
of two long chains or strands coiled
around each other to form a double
helical structure.
 Two chains runs in opposite
direction.

8. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
Salient features of Watson and Crick model
 DNA consists of nucleotides and a nucleotide consist of nitrogenous bases, pentose
sugar and phosphoric acid.
 Adenine forms double bond with thymine and Guanine forms triple bond with
cytosine.
 The bond between nitrogenous base is loose hydrogen bond. In a DNA two strands
are coiled with each in a ladder like manner just like a rope stair is twisted to form a
spiral. It has diameter of about 20 angstrom.
 A DNA consist of minimum 10 nucleotides and the total length of DNA is 34
angstrom.
 DNA is a double helix structure and the distance between two adjacent nucleotides
is about 3.4 angstrom.
 There are 4 types of deoxyribonucleotides that occurs in DNA- (i) dAMP (ii)
dGMP(iii) dCMP (iv) dTMP

9. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
Salient features of Watson and Crick model
 Phosphodiester bonds are formed between 5'C of sugar of another nucleotide.
Hence known as 3',5' - phosphodiester bond.
 Watson and Crick model of DNA is right handed i.e. it runs in clockwise
direction . The model is B form of DNA.
 DNA can be coiled like a rope in a process called DNA super coiling. In this
process if the DNA is twisted in clockwise direction then +ve super coiling
and bases are held more tightly together, whereas if the DNA is twisted in
anticlockwise manner then it is called -ve super coiling.
 In nature most of the DNA has -ve super coiling that is introduced by enzyme
topoisomerase.

10. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
Salient features of Watson and Crick model
 Two strands of double helix are anti-parallel.
 Each polynucleotide chain has sugar-phosphate backbone with nitrogenous
base directed inside the helix. These bases are stacked on top of each other
like a ladder fashion.
 The nitrogenous bases of anti-parallel polynucleotide strands are linked
through hydrogen bonds. There are2 hydrogen bonds A and C where as 3
between H and C.
 The hydrogen bonds are the only attractive forces between the two
polynucleotide of the double helix. they serve two hold the structure
together.

11. COMMUNITY LEVEL PHYSIOLOGICAL
PROFILING
CONCLUSION
 DNA is very important for life.
 From the helical structure of DNA it is confirm that Adenine pairs only with
thymine whereas Cytosine with Guanine.
 So the number of adenine and cytosine is equal with the number of thymine
and guanine respectively.