Chapter 2 - The molecular nature of genes. Before we begin to study in detail the structure and activities of genes, and the experimental evidence underlying those concepts, we need a fuller outline of the adventure that lies before us. Thus, in this chapter and in chapter 3, we will fl esh out the brief history of molecular biology presented in chapter 1. In this chapter we will begin this task by considering the behavior of genes as molecules. | Molecular Biology Fourth Edition Chapter 2 The Molecular Nature of Genes Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Nature of Genetic Material Historical Background Miescher isolated nuclei from pus (white blood cells) in 1869 Found a novel phosphorus-bearing substance = nuclein Nuclein is mostly chromatin, a complex of DNA and chromosomal proteins End of 19th century – DNA and RNA separated from proteins Levene, Jacobs, et al. characterized basic composition of DNA and RNA 2- Transformation in Bacteria Key experiments done by Frederick Griffith in 1928 Observed change in Streptococcus pneumoniae — from virulent (S) smooth colonies where bacterial had capsules, to avirulent (R) rough colonies without capsules Heat-killed virulent colonies could transform avirulent colonies to virulent ones 2- Outline of Griffith’s Transformation Experiments 2- DNA: The Transforming . | Molecular Biology Fourth Edition Chapter 2 The Molecular Nature of Genes Lecture PowerPoint to accompany Robert F. Weaver Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Nature of Genetic Material Historical Background Miescher isolated nuclei from pus (white blood cells) in 1869 Found a novel phosphorus-bearing substance = nuclein Nuclein is mostly chromatin, a complex of DNA and chromosomal proteins End of 19th century – DNA and RNA separated from proteins Levene, Jacobs, et al. characterized basic composition of DNA and RNA 2- Transformation in Bacteria Key experiments done by Frederick Griffith in 1928 Observed change in Streptococcus pneumoniae — from virulent (S) smooth colonies where bacterial had capsules, to avirulent (R) rough colonies without capsules Heat-killed virulent colonies could transform avirulent colonies to virulent ones 2- Outline of Griffith’s Transformation Experiments 2- DNA: The Transforming Material In 1944 a group used a transformation test similar to Griffith’s procedure taking care to define the chemical nature of the transforming substance Techniques used excluded both protein and RNA as the chemical agent of transformation Other treatments verified that DNA is the chemical agent of transformation of S. pneumoniae from avirulent to virulent 2- Analytical Tools Physical-chemical analysis has often used: Ultracentrifugation Used to estimate size of material Electrophoresis Indicated high charge-to-mass ratio Ultraviolet Absorption Spectrophotometry Absorbance of UV light matched that of DNA Elementary Chemical Analysis Nitrogen-to-phosphorus ratio of , not found in protein 2- DNA Confirmation In 1940s geneticists doubted use of DNA as it appeared to be monotonous repeats of 4 bases By 1953 Watson & Crick published the double-helical model of DNA structure and Chargaff had shown that the 4 bases were not present in equal proportions Hershey and Chase demonstrated .
