This module provides an introduction to plasmids, small circular DNA molecules that replicate independently of the host cell DNA. The module focuses on yeast overexpression plasmids, which have replication origins and selectable markers that allow them to be propagated in either bacteria or yeast. The plasmids also contain promoters that control expression of a cloned gene in Saccharomyces cerevisiae. In this module, students will:understand the various features that have been engineered into plasmids for experimental purposeslearn how the physical properties of plasmids are used in their purificationisolate plasmids from E. coli estimate plasmid concentration and purity using ultraviolet spectroscopyThis module is part of a semester-long introductory labortory course, Investigations in Molecular Cell Biology, at Boston College