DNA The Hereditary Material

The Discovery of DNA 1869 – Friedrich Miescher investigated chemical composition of DNA using pus cells. At the time, proteins were thought to be hereditary material. Miescher discovered the nuclei of cells contained a substance that does not act like protein. He called this substance nuclein. This caused debate – Is protein or nuclein the hereditary material?

Location of Hereditary Information 1930s Hammerling Experiment Experiment using Acetabularia, one-celled green alga Hypothesized that hereditary material was found in the foot and possibly the nucleus of the Acetabularia.

Hammerling’s Experiment Acetabularia Experiment Observations: –Caps that were removed regrew –Feet that were removed, did not regrow –Caps that grew matched the species of the foot not the stalk. Conclusions: –Hereditary information was found in the nucleus in the foot of the cell.

The Transforming Principle The nucleus contains the genetic information but scientists were still uncertain whether the chromosomes consisted of both proteins and DNA. 1920s - Frederick Griffith was trying to develop a vaccine against pneumonia. He obtained unexpected experimental observations that led him to believe that protein is not the hereditary material. Griffith Experiment

Some substance (the Transforming Principle) must have been transferred from the dead bacteria to the living non- virulent bacteria making it virulent 1944 – Avery, McCarty, MacLeod later showed that the Transforming Principle was DNA

Hershey and Chase Experiment 1952 – Hershey and Chase conducted experiments using bacteriophage T2 that infects a bacterial host. View experiment Conclusion: DNA, not protein is the hereditary material.

DNA Structure 1860s - Miesher discovered that nuclein is slightly acidic and composed of large amounts of P and N. 1920s – Determined that DNA comprises a deoxyribose sugar, a phosphate, and a nitrogen base DNA Structure Animation

DNA Structure Contributors Chargaff – adenine = thymine, cytosine = guanine Franklin – X-ray diffraction pattern suggesting a double helix shape Watson and Crick – Deduced structure of DNA using work of Chargaff, Franklin and Wilkins

DNA Replication and Repair DNA Replicates semi-conservatively

Meselson and Stahl Meselson and Stahl devised an experiment to suggest that DNA replication is semi-conservative. Meselson and Stahl Experiment Experiment 2

DNA Replication and Repair DNA Replication is a process comprising of: 1.Separating DNA strands 2.Building Complementary Strands 3.Quality Control DNA ReplicationDNA Replication Animation