Ellis Engelsberg and his colleagues examined the regulation of genes taking part in the metabolism of arabinose, a sugar (E. Engelsberg et al. 1965. Journal of Bacteriology 90:946-957). Four structural genes encode enzymes that help metabolize arabinose (genes A, B, D, and E). An additional sequence C is linked to genes A, B, and D. These are in the order D- A- B- C. Gene E is distant from the other genes. Engelsberg and his colleagues isolated mutations at the C sequence that affected the expression of structural genes A, B, D, and E. In one set of experiments, they created various genotypes at A and C and determined whether arabinose isomerase (the enzyme encoded by gene A) was produced in the presence or absence of arabinose (the substrate of arabinose isomerase) by cells with these genotypes. Results from this experiment are shown in the following table, where a plus sign (+) indicates that the arabinose isomerase was synthesized and a minus sign (-) indicates that the enzyme was not synthesized. Arabinose Arabir Genotype absent prese 1. C* A* 2. C A* 3. C A*/C* 4. CA/C A*

The tryptophan operon of E. coli represents an example of a gene regulatory system which is: a repressible system (normally turned on, but can be repressed) a repressible system (normally repressed, but can be turned on) an activator system (normally turned off, but can be activated) an activator system (normally activated, but can be turned off) all of the above

Describe the advantages and disadvantages for organisms that arrange genes in operons.

What would be the transcriptional output of the lac operon in an E. coli cell in the following 8 scenarios? Your answers must be one word each, selected from the following two options: 'high' and 'low.