Classic DNA Studies: I. Fredrick Griffith – 1928 Griffith was trying to find a vaccine against Streptococcus pneumoniae, a bacterium with two strains –one that causes pneumonia in mammals.

Avery, McCarty, MacLeod DNA was the “transforming agent” in Griffith’s experiment

Hershey and Chase DNA of bacteriophages enters bacterial cells, not protein capsid

Chargraff A=T and G=C as nucleotide ratios

Pauling, Wilkins, Franklin, Crick, Watson In 1953, Watson and Crick publish DNA structure

DNA – deoxyribonucleic acid Composed of nucleotides: a) deoxyribose sugar b) phosphate c) nitrogenous base Adenine and Guanine are purines Cytosine & Thymine are pyrimidines

Adenine pairs with Thymine via 2 H bonds Cytosine pairs with Guanine via 3 H bonds DNA double helix makes one full turn every 3.4 nm There are 10 base pairs per turn (.34 nm apart)

DNA replication In 1950s, Meselson and Stahl proved the semisconservative model of replication

DNA replication cast of characters I.DNA polymerase - adds nucleoside triphospates only by elongating in the 5’  3’ direction. Cannot start from scratch. II.Primase – adds complementary RNA primer to lagging strand for polymerase attachment III.DNA ligase – “welds” sugar phosphate backbones between non-continuous, synthesized strands

IV. Helicase – unwinds helix/separates strands V. Single stranded binding protein – holds original DNA strands apart during replication VI. Nuclease – can “cut out” improper DNA segments VII. Telomerase – carries an RNA template to elongate the 3’ end of a telomere by adding DNA nucleotides