WATSON & CRICKDOUBLE 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 baseadenine, 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 DNAFranklin with wilkins at kings college worked on B DNAX- RAY DIFFRACTION METHODFranklin-wilkins CLASHESFranklin left kings college… but completed her unpublished work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
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