DNA: The Hereditary Material Is protein or DNA the hereditary material?

Most scientists thought proteins carried genetic information because DNA had a much simpler structure than proteins. Most scientists thought proteins carried genetic information because DNA had a much simpler structure than proteins.

Friedrich Miescher (1869) He used pus cells to investigate the chemical composition of DNA. He used pus cells to investigate the chemical composition of DNA. He discovered that the nuclei of cells contain large quantities of a substance that does not act as a protein. He discovered that the nuclei of cells contain large quantities of a substance that does not act as a protein. He called this substance nuclein. He called this substance nuclein.

Joachim Hammerling (1930)

His experiments suggested that the hereditary material is located in the nucleus. His experiments suggested that the hereditary material is located in the nucleus. He conducted experiments on a one-celled green alga-Acetabularia He conducted experiments on a one-celled green alga-Acetabularia

Frederick Griffith's Experiment (1920) - The Discovery of Transformation He wanted to find a vaccine against pneumonia caused by Streptococcus pneumonia He wanted to find a vaccine against pneumonia caused by Streptococcus pneumonia He used two varieties of streptococcus He used two varieties of streptococcus One variety of bacteria had a capsule (like a cell wall) – Type S One variety of bacteria had a capsule (like a cell wall) – Type S The other did not have a capsule. – Type R The other did not have a capsule. – Type R

Frederick Griffith's Experiment (1920) - The Discovery of Transformation

ExperimentResult Injection with live Type SMice contracted pneumonia and died Injection with live Type RMice lived, immune system destroyed the bacteria Injection with heat killed Type SMice remained healthy Injection with dead Type S and live Type R *Note: Neither of these forms caused disease before, but when placed together, something occurred to make the living Type R (naked) bacteria virulent. Mice contracted pneumonia and died

Conclusions Living bacteria acquired genetic information from dead bacteria - particularly the instructions for making capsules, thus transforming the naked bacteria into encapsulated bacteria. Living bacteria acquired genetic information from dead bacteria - particularly the instructions for making capsules, thus transforming the naked bacteria into encapsulated bacteria. The transforming agent was discovered to be DNA. DNA was isolated and added to live naked bacteria, and they were transformed into the encapsulated kind The transforming agent was discovered to be DNA. DNA was isolated and added to live naked bacteria, and they were transformed into the encapsulated kind Some scientists still remained unconvinced. Some scientists still remained unconvinced.

The Hershey-Chase Experiment – Bacteriophage (1952)

Conclusions It was the phosphorus-rich DNA, not the protein, which was the molecule of heredity.

………..By 1920: It was known that DNA consisted of three components: 1. Deoxyribose sugar 2. Phosphate group (negatively charged) 3. nitrogenous base

Recall, the variation among the Nitrogen bases: