Evidence for DNA as the genetic code
The discovery of transformation by Griffith in 1928 started them idea that genetic material is nucleic acid. ... The studies of Avery showed chemically in 1944 that the transforming principle is deoxyribonucleic acid (DNA). This was a great surprise, because, at the time, DNA was not even recognised as a component of Pneumococcus. DNA was however recognised as a major component of eukaryotic chromosomes. ... “The inducing substance, on the basis of its chemical and physical properties, appears to be a highly polymerised and viscous form of DNA. ... ” The structure of DNA Deoxyribonucleic acid is a linear polymer of up to a hundred million monomer units (nucleotides). DNA contains only four different nucleotides. ... Thus a single DNA strand is a phosphate- deoxyribose polymer with purine and pyramidine bases as side groups. ... The structure and orientation of a DNA strand showing the direction of synthesis from 5` to 3`. THE NATIVE STATE OF DNA IS A DOUBLE HELIX OF TWO ANTIPARALLEL CHAINS WITH COMPLEMENTARY NUCLEOTIDE SEQUENCES. DNA does not normally exist as a single strand, it has a tendency to associate with another, complementary strand. ... In theory either purine could pair with either pyramidine, but in natural DNA A pairs with T and C pairs with G. Two polynucleotide chains can, in principle, form either a right-handed or a left handed or a left handed helix, but the geometry of the sugar-phosphate backbone is more conducive to a right-handed helix, therefore natural DNA is right-handed.