Why does arabinose make bacteria glow

Here are the before and after shots:. Why did we do this experiment? For one, it looks really cool when you put a gene from a jellyfish into a bacteria and then the protein makes it glow under UV light. But the real reason was to compare protein expression systems in E. The plasmid also contains resistance to ampicillin, an antibiotic that inhibits the cell wall formation in gram-negative bacteria like E.

Here is a map of the arabinose induced pGLO plasmid :. Arabinose is a simple plant sugar and is used as food by bacteria like E. The bacterial genes for arabinose digestion are not expressed unless arabinose is present. No need to waste all that energy on nothing, right? When arabinose is present, however, these genes get turned on and arabinose is broken down.

When arabinose runs out, the genes turn off. Three structural genes araB , araA , araD or BAD encode for enzymes used in the digestion of arabinose in bacterial cells. Another gene called araC produces a protein that regulates the expression of BAD. The a raC protein also acts to negatively control its own synthesis.

In other words, the araC protein binds to its own operator and prevents more araC transcription. The presence of both the araC protein and arabinose cause the expression of BAD. Arabinose binds to the araC protein and causes a change in its shape, which then allows both to bind to the regulatory region known as the activator site.

These three genes can now be transcribed and the resulting RNA can be translated into protein. The unique fluorescent property of GFP allows real-time monitoring of extraction and purification, modeling key processes used in biotechnology to produce and purify designer proteins with commercial or research value. Use these short, instructional videos to enrich lessons about bacteria, bacterial transformation, and the green fluorescent protein GFP.

Investigate the functional elements of pGLO bacterial transformation, including heat shock, antibiotic selection, promoters, and satellite colony formation.

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Investor Relations Explore all. The other is AraC, which is a regulatory protein that controls the expression of the operon. The arrows on the transcription units represent the direction of transcription. Transcription goes in different directions for these two transcription units, because they are transcribed from different strands of the DNA. Like the lac operon, the AraBAD operon is negatively controlled by a repressor protein.

When no arabinose is present, the repressor protein called AraC in this case binds to operator regions in the DNA and blocks transcription of the operon. In the diagram, the line represents the double-stranded DNA. AraC proteins form a homodimer : two identical proteins bound together. In this situation, AraC is acting as a negative regulator of transcription in other words, a repressor.

In other words, when the level of AraC protein builds up in the cell, it turns off the AraC gene, so no more AraC protein is synthesized until the amount of AraC protein decreases. Therefore, there is always a small amount of AraC protein present. Arabinose acts as an allosteric regulator of AraC, changing which DNA sites it binds to and how it forms a dimer.

Remember that arabinose is the sugar that gets catabolized by the proteins of the AraBAD operon. When arabinose is added to the environment in which E. The AraC protein lets go of one of its former binding sites and attaches to another. In this diagram, the two copies of AraC with the green "A" arabinose molecules attached sit side by side on the DNA; in fact, they are stuck together as a new kind of dimer. In this position, AraC no longer acts as a repressor.

In eukaryotic gene regulation, a protein that attaches near a promoter and assists RNA polymerase is called a transcription factor. For some reason, that term is less commonly used for bacterial genes, but I think it fits AraC perfectly in this situation. You encountered this protein acting on the lac operon. The AraBAD operon, like the lac operon, encodes proteins for catabolizing an uncommon type of sugar. In both cases, glucose is the preferred energy source, because fewer enzymes are required.

When E. For maximum expression of the GFP gene in pGLO, you'll need to culture your bacteria in plates with arabinose and no glucose. You'll be able to see how strongly glucose affects GFP expression by looking at your pGLO plates grown with and without glucose added to the medium.