13.1 The Structure of DNA I. DNA: The Genetic Material A. Genes are the instructions for inherited traits. B. Before the 1950’s we didn’t know what genes were made of. C. DNA 1. Deoxyribonucleic Acid a. the primary material in genes that causes recognizable, inheritable characteristics

b. made up of four different subunits c. early scientists thought it too simple to be genetic material II. Searching for the Genetic Material A. 1928 Frederick Griffith, an English public health bacteriologist 1. Working with vaccines – a substance of killed or weakened microorganisms used in the body to produce immunity 2. Chose two strains of bacteria

a. the S-type had a capsule that. made it virulent – able to cause a. the S-type had a capsule that made it virulent – able to cause disease & the R-type had no capsule 3. The Experiment a. S-type killed mice but did not when it was heat killed b. R-type did not kill mice, when mixed with heat killed S-type it became deadly 1. This proved that R-type underwent a transformation 4. 1944 it was announced that DNA was genetic material

B. 1940’s, Oswald Avery 1. Wanted to determine whether the transforming agent was protein, RNA, or DNA. 2. Concluded that DNA is responsible for transformation. C. Hershey and Chase 1. 1952 conducted an experiment with bacteriophage – virus that infects bacteria a. T2 bacteriophage attaches to bacteria and injects genetic info.

b. Once inside bacteria, virus. copies hundreds of itself & b. Once inside bacteria, virus copies hundreds of itself & eventually cause the bacteria to burst c. DNA contains phosphorous – given radioactive treatment to track d. Protein has sulfur – given radioactive treatment to track 2. Radioactive phosphorous found inside bacteria after experiment 3. Proved that DNA was genetic info carrier and not protein

III. The Shape of DNA A. Nucleotides 1. long thin molecule that makes up DNA 2. 3 parts a. phosphate group b. 5 carbon sugar – called deoxyribose c. nitrogen base – could be one of four 1. Purines – has double carbon ring a. adenine b. guanine 2. Pyrimidines – has single carbon ring a. thymine b. cytosine

B. Erwin Cargaff created base paring rules 1. adenine --- thymine 2. guanine ---- cytosine IV. Discovering DNA’s Structure A. 1952 Maurice Wilkins and Rosalind Franklin use x-ray diffraction 1. determine that DNA is a double helix of 2 or 3 coiled chains B. 1953 Watson and Crick 1. discovered 3 dimensional double helix or “spiral staircase” 2. DNA looks like twisted ladder 3. Each side of the ladder is complimentary ex.- T C G A A C T A G C T T G A