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college worked on B DNAX- RAY DIFFRACTION METHODFranklin-wilkins CLASHESFranklin left kings college… but completed her unpublished work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