Classic Experiments in Molecular Biology

Running head: CLASSIC EXPERIMENTS IN MOLECULAR BIOLOGY

Classic Experiments in Molecular Biology

The Transforming Principle: Identifying the Molecule of Inheritance

Meselson and Stahl Experiment: The Nature of DNA Replication

Abstract

This two part case study describes experiments in molecular biology. It shows the methods used by the scientists, how the information was given to the science community. The first part ‘The Transforming Principle: Identifying the Molecule of Inheritance” tells of the necessity and the investigation methods, tools and the type of data generated to form a hypothesis. The results are then presented to show how conclusions may be formed. This part of the case shows how the investigation was initiated with a published paper by Fred Griffith at the British Ministry of Health who was studying the bacterium Streptococcus pneumonia, an important pathogen at the time of 1928, because of the related diseases and their transformations. This material was useful to observe as some forms of S. pneumonia cause disease (pneumonia) and some do not. When different strains are observed in the lab, the scientists could make a good guess on the pathogenicity (disease causing ability) of S. pneumonia. The smooth strain was determined as the disease causing strain because of its coating and ability to hide from the immune system to cause disease, and the rough strain which was recognized by the immune system and is destroyed thus preventing disease. Cells can be fractionated into different chemical components. Both Griffith and Avery found cellular fractions that could transform non-disease causing bacteria into disease causing bacteria. The Meselson and Stahl experiments added new tools and explained the nature of DNA replication. The three postulated methods are given, Semi-Conservative, Conservative, and Dispersive. These new studies used additional methods such as the Nitrogen elements 14N and 15N to determine the results of the DNA...