Chapter 2. Molecular Biology II

General Purpose

Lab 12 Pre-Lab—Analysis of Bacterial Phenotypes

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This pre-lab will present some of the general concepts related to some of the techniques used in the fields of microbiology and molecular biology and how these techniques relate to understanding the relationship between DNA, genes, and traits expressed by an organism.

Learning Objectives

General Purpose

Develop a basic understanding of some of the techniques used in the field of molecular biology.

Conceptual

Gain an understanding of the relationship between DNA nucleotide sequences and phenotype.

Background Information

When an organism is transformed, the addition of the genes present on the plasmid DNA changes the genotype of the organism. These new genes may be expressed in the organism resulting in a change in the phenotype of that organism. There are many phenotypic characteristics that can be used to trace the presence of plasmids (e.g., antibiotic resistance, colony color, fluorescence, etc.).

The same strain of E. coli may have different phenotypic characteristics depending on which plasmid it is carrying. Here is an example of a phenotypic difference based on bacterial fluorescence. Figure 12-3 shows a photo of E. coli streaked on a Petri dish shown under white light.

Figure 12-3. E. coli streaked on a Petri dish under white light.

The two halves of the Petri dish have E. coli transformed with different plasmids. Both plasmids produce bacterial colonies that appear white under white light. One of the plasmids contains the gene for a protein that fluoresces under ultraviolet light. Figure 12-4 shows the same plate under ultraviolet light.

Figure 12-4. E. coli streaked on a Petri dish under ultraviolet light.

The bacteria on the right side of the plate fluoresce under UV light.

Pre-Lab Quiz

Proceed to the Pre-Lab Quiz