Biologists on Genetics Erwin Chargaff

(1905-2001)

Relative quantities of the nitrogen bases found in DNA

Background

About Erwin Chargaff

Born in Austria on August 11, 1905 Receive a doctorate degree of Chemistry

from the University of Vienna in 1928 1944 - Study of DNA and its four chemical

bases - adenine, cytosine, guanine and thymine

Using chromatography technique Discover amounts of adenine and thymine

were equal, as were the amounts of cytosine and guanine

The 4 nitrogen bases

The 4 nitrogen bases - Purines Consist of a six-membered and a five-membered nitrogen-containing ring, fused together

Adenine = 6-amino purine

Guanine = 2-amino-6-oxy purine

The 4 nitrogen bases - Pyrimidines

Have only a six-membered nitrogen-containing ring

Uracil = 2,4-dioxy pyrimidine

Thymine = 2,4-dioxy-5-methyl pyrimidine

Cytosine = 2-oxy-4-amino pyrimidine

Chargaff's first parity rule

Stated that purines pair with pyrimidines, specifically A with T and C with G

E.g ACGATGCCGTA

With pairing between complementary bases in the "top" and "bottom" strands 

Chargaff's second parity rule

% of A approximately equals % of T; % of G approximately equals % of C for single strands of DNA

Cluster rule

Stated that pyrimidines often occur in runs or clusters, and hence on the complementary strand purines do likewise

GC rule

Stated that (G+C)% is constant within a species, but often differs between species.