SECTION B 11. Imagine the two situations shown in the figure below. In cell I, t
ID: 273872 • Letter: S
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SECTION B 11. Imagine the two situations shown in the figure below. In cell I, transient signal induces the synthesis of protein A, which is a gene activator that turns on many genes including its own. In cell I, a transient signal induces the synthesis of protein R, which is a gene repressor that turns off many genes including its own. a. What is the resulting transcription level after receiving the transient signal in cell I and cell II respectively? b. In which, if either, of these situations will the descendants of the original cell "remember" that the progenitor cell had experienced the transient signal? Explain your reasoning. c. What effect would an insulator have that sits upstream of the gene activator (cell 1)? Does the insulator also influence the self-activation of the activator gene? Explain. (A) CELLI transient OFF signal -? turns on transcription of activator mRNA activator protein turns on its own transcription gene activator (B) CELL II transient signal OFF turns on transcription of repressor mRNA repressor protein turns off its own transcription gene repressorExplanation / Answer
Please find the answers below:
Answer a: According to the information, the cell 1 experiences negative regulation whereas cell 2 experiences positive regulation secondary to the transient signal. Hence, once transcription starts, the cell 2 will experience up-regulation in gene expression due to positive feedback loop mechanism whereas cell 1 will experience down-regulation in gene expression due to negative feedback mechanism.
Answer b: Both the genes are under separate promoter controls and hence are maintained as separate cistrons. Hence, both the descendants of cells 1 and 2 will actually able to remember their choices of gene expression secondary to the transient signal.
Answer c: As an insulator sequence prevents binding of a protein/element to the DNA, it prevents the down-stream signalling events. In case of cell 1, this insulator will thus prevent binding of the release factor and hence prevent halting of gene expression. Ultimately, the gene expression of cell 1 will increase. Conversely, the gene expression of cell 2 will decrease.
Depending upon the nature and localization of insulator on the gene, it can up- or down-regulate the gene expression. However, autonomous onset of gene expression does not take place secondary to insertion of an insulator gene.
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