Structure of DNA

1. By
SYED AASIM HAQ
ROLL NO- 2015ZYM-033
ENROLLMENT NO- GI8470
DEPARTMENT OF ZOOLOGY
ALIGARH MUSLIM UNIVERSITY
STRUCTURE OF DNA (DE-
OXYRIBONUCLEIC ACID)

2. DNA is a complex molecule found in all organisms
(except RNA viruses). The primary function of DNA is
to store and transmit genetic information that tells cell
which protein to make and when to make.
Eukaryotes store most of their DNA in nucleus and
some in organelles(mitochondria and chloroplast)
where as Prokaryotes store their DNA in the cytoplasm.
The total amount of DNA on earth is about 5 x 1037 bp
and weight about 50 billion tones.
INTRODUCTION

3. Frederick Miescher(1869), isolated DNA from nuclei
of WBCs.
Rosalind Frankling and Maurice Wilikins
used X-ray crystallography to capture
the first image which suggest
that it had spiral or helical structure
and even width.
Erwin Chargaff- observed that amount of thymine was
always equal to adenine and the amount of cytosine was
always equal to guanine in cells of different organisms.
Watson and crick(1953), proposed the DNA double
helical structure.
HISTORY OF DNA

4. COMPONENTS OF DNA
DNA is made up of repeating units
of nucleotide . Each nucleotide is
composed of 3 molecules bounded
together ;
Nitrogenous Base(Purines and pyrimidine's)
De-oxyribose sugar
Phosphate

6. James D Watson and Francis Crick(1953) proposed
double helical structure(Model) of DNA. It was based on
two major kinds of evidence.
1) X-ray diffraction data of DNA obtained by
Rosalind's and Wilkins.
2) Erwin Chargaff's observations; Chargaff's rule.
Watson, Crick and Wilkins were awarded
Nobel prize in 1962 in medicine. Rosalinds died of
cancer before 1962 and Nobel prize is not awarded
posthumously.
DOUBLE HELICAL STRUCTURE
OF DNA

7. DNA Double Helix
DNA consists of two antiparallel
polynucleotide chains wound around
each other on central axis.
The Sugar-phosphate backbone is
present on the outside with base
oriented towards central axis.
Bases are held together by H- bonds.
Pairing is complementary.
 A=T and G ≡C

8. The base pairs are 3.4Å apart
in the DNA helix.
There are 10 bases per
turn(34Å).
Diameter of the helix is 20Å.
There are two types of grooves
of unequal sizes that is Major
groove(22Å) and minor
groove(12Å).These grooves are
formed due to non-symmetrical
location of two strands.

9. Conformation of DNA
A-DNA B-DNA Z-DNA
Right handed helix Right handed Left handed
Short and broad Long and thin Longer & thinner
Helix diameter ; 25.5Å 20Å 18.4Å
Helix width ; 25Å 34Å 47Å
Bases per turn ; 11 10 12
Inter Base pair distance ; 2.5Å 3.4Å 3.8Å

10. Thank you