WATSON & CRICK
DOUBLE HELIX MODEL OF DNA
Presented by: fatima kharbe

WHAT IS DNA?
A. Nucleotide:
1. Thousands of repeating units that
make up the DNA (DNA is a polymer)
a) a phosphate group
b) a deoxyribose molecule (5-carbon
sugar)
c) a nitrogenous base
adenine, thymine, guanine, cytosine
(There are four different types of nucleotides,
depending on which of the four bases
is present- A, T, C, or G)

BACKGROUND HISTORY
• Friedrich Miescher: 1869 first identified what he called
“NUCLEIN”.
• Fischer: 1880 identified purines & pyrimidines.
• Kossel: 1910 demonstrated 2 purines(A&G) & 2 Pyrimidines
(C&T)
• Levene: 1910 first to discover the 3 major components of a
single nucleotide.
• Robert Fuelgen: 1914 demonstrated a colour test known as
Fuelgen Reaction for DNA
• Avery,Macleod McCarthy:1944 demonstrated that DNA is
directly involved in inheritance
• Chargaff: 1947 Purines = Pyrimidines

Pauling & Corey:1951 suggested an alpha helicle stucture. Their
model consists of three intertwined chains, with the
phosphates near the fibre axis, and the bases on the outside.
Rosalind Frankin: the dark lady behind the discovery of DNA
Franklin with wilkins at kings college worked on B DNA
X- RAY DIFFRACTION METHOD
Franklin-wilkins CLASHES
Franklin left kings college… but completed her unpublished work

Rosalind Franklin Maurice Wilkins
King’s College
James Watson Francis Crick
Cambridge University
Caltech University
Linus Pauling

FRANKLINS WORK
• Wilkins & Franklin:1950
• Watson was shown this
picture by Wilkins in early
1953.
From the picture it was
possible to calculate:
1) The molecule was not
linear but helix
• 2)Distance between the
bases 3.4A
• 3)Length of period every
34A

• On Feb. 28, 1953, Francis Crick
walked into the Eagle pub in
Cambridge, England, and, as
James Watson later recalled,
announced that "we had
found the secret of life."
Actually, they had. That
morning, Watson and Crick
had figured out the structure
of deoxyribonucleic acid, DNA.
And that structure — a
"double helix" that can "unzip"
to make copies of itself —
confirmed suspicions that DNA
carries life's hereditary
information.

WATSON’S AND CRICK MODEL
• DNA (Deoxyribonucleic Acid)
• DNA is a double stranded molecule that is twisted into a Helix (Spiraling
Staircase)

• Each strand consists of:
• 1) A Sugar Phosphate Backbone

• PHOSPHODIESTER
BRIDGES
• HYDROGEN BONDS
• BASE PAIRING
• CHARGAFFS RULE
• A+T=G+C
• ANTIPARALLEL

OTHER FORMS OF DNA

• In 1962 Watson, Crick & Wilkins won the Nobel Prize for their
• discovery of the structure of DNA

BIBILOGRAPHY
• Molecular biology of gene by Watson
• Lehninger principles of biochemistry
• Cytology & molecular biology by Verma&
Agarwal
• The structure of DNA by WATSON & CRICK
Downloaded from symposium.cshlp.org on
• ALBERTS molecular biology of the cell
• Images from google.com

THANK YOU