Transcription and Gene Expression in Bacteria Student Laboratory Kit Introductio

Question

Transcription and Gene Expression in Bacteria Student Laboratory Kit Introduction Explore the effect of temperature on the expression of specific genes in Serratia marcescens bacteria. Biological Concepts Microbiology Gene expression Enzymes Background All living organisms contain many genes encoded in their DNA sequences. Each gene contains the information needed for the cell to produce a specific protein or enzyme required to carry out a particular biochemical function or to fulfill process. Factors such as pH, light, and temperature may cause certain genes to be "turned on" or to be "turned off" under certain conditions. In other words, although the genes are always present in the organism's DNA, a variety of stimulants or inhibitors may cause gene expression--the transcription of the gene DNA to produce mRNA, which is ultimately translated into the proteins required for specific cellular processes-to start or stop. If gene expression is turned off, the appropriate mRNA is not produced and translation will not occur. The corresponding proteins are not produced and the cellular function controlled by the protein stops. Therefore the gene is no longer expressed. In this activity, the study organism is Serratia marcescens a Gram-negative common soil bacterium, which may be red, pink. white or colorless. The presence of several specific enzymes within S. marcescens are required for the dark, red-colored pigment prodigiosin to be produced. Studies indicate that the prodigiosin pigment may have anti-fungal. antibacterial and antiprotozoan properties, which may help the bacteria ward off "competitors." Although the bacteria will grow and thrive over a fairly wide temperature range (17-43 degree C), the gene for prodigiosin is only expressed in part of that temperature range. If the bacteria are grown at a temperature in which the genes are expressed, then the enzymes responsible for the synthesis of prodigiosin are produced, the pigment will be present and the bacteria will appear red in color. Alternatively, when the bacteria are grown at a temperature in which the enzymes responsible for the synthesis of prodigiosin are not transcribed, no pigment is made and the bacterial colonies will appear white or colorless. Experiment overview In this activity S.marcescens will be grown on nutrient agar at room temperature (approx. 25degree C) and at human body temperature (37 degree C). The effect of temperature on differences in gene expression will be defined based on the presence or absence of the prodigiosin pigment. Pre-Lab Questions (Use a separate sheet of paper to answer the following questions.) Why is it considered proper practice to label the bottom of the Petri dish rather than the lid? Explain the term gene expression in your own words. Write a hypothesis for what you predict will be observed at the two different temperatures based on information in the Background section.

Explanation / Answer

1) The bottom of the Petri dish is labelled rather than the lid because of the following reasons:

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