The discovery of the genetic role of DNA began with the research of Fredrick Griffith in Griffith worked with 2 strains of bacterium, one pathogenic (SMOOTH) and one harmless (ROUGH) When he mixed heat-killed remains of the pathogenic strain with living cells of the harmless strain, some of the living cells became pathogenic. He called this phenomenon Transformation, now defined as a change in genotype and phenotype due to assimilation of foreign DNA.

In 1952, Alfred Hershey and Martha Chase preformed experiments showing that DNA is the genetic material of a phage known as T2. They designed an experiment showing that only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection. They concluded that the injected DNA of the phage provides the genetic information.

 Watson and Crick used X-ray diffraction photos from Franklin and Wilkins to conclude that DNA is made up of two antiparallel sugar-phosphate backbones.  They determined that the two strands of DNA are antiparallel nature of DNA - the strands run in opposite directions. One strand runs 3' to 5' while the second strand runs 5' to 3'.  They used Chargaff’s rule to determine that the nitrogen bases connected the two strands of DNA -Adenine binds to Thymine while Guanine binds to Cytosine.

Nucleotides are the building blocks of nucleic acids (DNA and RNA) Each nucleotides is made up of the following: Sugar Phosphate Nitrogen base Phosphate group of one nucleotide bonds to sugar of adjacent nucleotide forming a sugar-phosphate backbone Nitrogen bases can be either: Purines – adenine and guanine; double ring P y rimidines – th y mine, c y tosine and uracil; single ring structure

Deoxyribonucleic Acid Ribonucleic Acid  DNA › Sugar = deoxyribose › Nitrogen bases = A, T, G and C › Strands = double stranded  RNA › Sugar = ribose › Nitrogenous bases = A, U, G and C › Strands = single strand; 3 types

5’ and 3’ refer to the position of the carbon in the sugar of the nucleotide In a nucleotide the phosphate group attaches to the 5’ carbon and nitrogen base attaches to the 1’ carbon 3’ carbon is open to attach to the phosphate of an adjacent nucleotide

 Double Helix – backbones/uprights consist of alternating sugars and phosphates; rungs are nitrogen bases; nitrogen bases are held together by hydrogen bonding;  The two strands run in opposite directions – we say they are “antiparrell”  Adenine bonds to Thymine; Guanine bonds to Cytosine