The regulatory sequences of the operon controlling arabinose metabolism (ara operon) were studied to determine whether bacteria can respond to changes in nutrient availability. It is predicted that if those regulatory sequences are functioning properly, the bacteria will produce the enzymes involved in arabinose metabolism (structural genes \(B\), \(A\), and \(D\)) in the presence of arabinose.

If a gene that encodes a green fluorescent protein (GFP) is substituted for the structural genes of the operon, activation of the regulatory sequences can be assayed by GFP expression. A culture of E. coli cells underwent a transformation procedure with a plasmid containing the regulatory sequences of the ara operon directly upstream of the gene encoding the GFP. The plasmid also confers ampicillin resistance to bacteria. Samples were then plated on different types of culture media. (Note: The GFP fluoresces only under UV light, not under white light.) The table below shows the results.

Which of the following can best be used to justify why the GFP is expressed by E. coli cells after transformation with the plasmid?

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Although there is a lot of reading and data, we should be able to follow along.

The first paragraph notes that bacteria will produce the enzymes involved in arabinose metabolism in the presence of arabinose. The second paragraph notes that we can use a GFP assay. If the bacteria was supposed to produce the enzymes, it will now glow green. Based on the table, bacteria in the presence of arabinose were green.

There were still white bacteria in the 3^rd trial since an antibiotic was not used. A mixture of bacteria was present - some with the plasmid and some without the plasmid that contained the GFP.