By

SYED AASIM HAQ

ROLL NO- 2015ZYM-033

ENROLLMENT NO- GI8470

DEPARTMENT OF ZOOLOGY

ALIGARH MUSLIM UNIVERSITY

STRUCTURE OF DNA (DE-OXYRIBONUCLEIC

ACID)

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

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

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 sugarPhosphate

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

DNA Double HelixDNA 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

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.

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

Thank you