7 Imagine the following two situations LAN CELLI (see figure to the right). In c
ID: 80354 • Letter: 7
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7 Imagine the following two situations LAN CELLI (see figure to the right). In cell I, a transient signal induces the synthesis of protein A, which is a transcriptional gene activator turns on transcription activator protein of activator mRNA turns on its own activator that turns on many genes including its own. In cell II, a transient (B) CELLll signal induces the synthesis of protein OFF transient R, which is a transcriptional repressor R that turns off many genes including its gene repressor turns on transcription repressor protein own. In which, if either, of these of repressor mRNA turns off its own transcription situations will the descendants of the original cell "remember" that the progenitor cell had experienced the transient signal? Explain your reasoning. 8 In the absence of glucose, E. coli can proliferate by using the pentose sugar arabinose. As shown in Figure Q4, the arabinose operon regulates the ability ofE. coli to use arabinose. The araA, araB, and araD genes encode enzymes for the metabolism of arabinose. The araC gene encodes a transcription regulator that binds adjacent to the promoter of the arabinose operon. To understand the regulatory properties of the Arac protein, you engineer a mutant bacterium in which the araC gene has been deleted and look at the effect of the presence or absence of the AraC protein on the AraA enzyme. ara promoter RNA polymerase binding site Figure Q8 A. If the Arac protein works as a gene repressor, would you expect araA RNA levels to be high or low in the presence of arabinose in the araC mutant cells? What about in the araC mutant cells in the absence ofarabinose? Explain your answer. B. Your findings from the experiment are summarized in Table Q8.Explanation / Answer
Answer:
7. The induction of a transcriptional activator protein that stimulates its own synthesis can create a positive feedback loop that can produce cell memory. The continued self-stimulated synthesis of activator A can in principle last for many cell generations, serving as a constant reminder of an event that took place in the past.
By contrast, the induction of a transcriptional repressor that inhibits its own synthesis creates a negative feedback loop which ensures that the response to the transient stimulus will be similarly transient. Because repressor R shuts off its own synthesis, the cell will quickly return to the state that existed before the signal.
(Since there are more than 1 question, the first question have been answered according to the rules of Chegg)
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