You are working on a monosaccharide called Gummyose Gummyose

You are working on a monosaccharide called Gummyose. Gummyose requires the enzymes X, Y, and Z. The genes encoding these enzymes are part of one operon, and the product of gene N (N protein) regulates the transcription of these three genes. In a normal cell, protein A is always produced. A diagram of this operon is shown below. Give a brief definition of an operon. In a cell where there is a high level of N protein, you detect no transcription of genes X, Y, and Z. The N protein is a repressor or an activator? In further study, you discover that transcription of the N gene is controlled by protein A (protein A is the product of gene A shown in the diagram), and Gummyose binds to the N protein. You examine the transcription of genes N, X, Y, and Z in cells where gene A is normal (A+) and where gene A is not functional (A-) and in the presence (+) and absence (-) of Gummyose. The data is shown below Given the results above, what does protein A do? Given the results above, what does Gummyose do?

Solution

a) An operon is a genetic regulatory system in prokaryotes with clusters of genes which code related proteins under the control of one promoter along with other sequences that are required in this regulation.They are polycistronic (contain multiple genes on a single mRNA during transcription and is then translated into different proteins.

b)Since there is no transcription of genes X, Y and Z, the N protein is acting as a repressor. In this example, the repressor is acting as a DNA binding protein which binds to the operator sequence (which is the site in the operon where the repressor binds so that the transcription is stalled) and inhibits the transcription of the operon.

c)i) Protein A is acting as an activator which is a protein that increases the trancription of gene N to produce protein N. This can be concluded from the table since whenever the gene A is transcribed, the trancript of N is generated.

ii) According to the data given, it can be concluded that transcription of genes X,Y, Z produces the corresponding enzymes which maybe required for the metabolism of gummyose. So, Gummyose is acting as an inducer which binds to the repressor protein N to cause a conformational change to protein N and its removal from the operator site so that the transcription of genes X, Y and Z occurs.