Saturday, April 2, 2011

DNA: Structure – People and History

RECALL:
-DNA is a polymer of nucleotides linked together by phosphodiester linkages
-A nucleotide consists of a five carbon sugar (ribose) with a phosphate group attached to carbon number 5, and a nitrogen base attached to carbon number 1 using a glycosyl bond.
-There are 4 base pairs (2 purines: 2 rings, and 2 pyramidines: 1 ring).
-They are grouped together as complimentary base pairs:
Cytosine (pyramidine) with Guanine (purine)
Thymine (pyramidine) with Adenine (purine)
-DNA consists of two anti-parallel strands in a double helical structure connected by hydrogen bonds.


1949—Erwin Chargaff
-analysed data from chemical analysis of DNA
-found Adenine and Thymine, Cytosine and Guanine, Purines and Pyramidines existed in equal proportions




1953—Rosalin Franklin, Maurice Wilkins
-used x-ray diffraction to analyse DNA structure
-suggested double helical structure (2nm diameter, 3.4nm helical twist)
-Wilkinson presented data to Watson and Crick before it was published


1953—Watson, Crick
-presented DNA structure based on Chargaff, Franklin and Wilkin’s observations

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