In all cases please give a detailed justification for your answer. If it is a de
ID: 3164632 • Letter: I
Question
In all cases please give a detailed justification for your answer. If it is a descriptive problem, a few sentences to a paragraph will do. If it is a problem involving any calculations, please show your work and briefly describe your reasoning. You are scored both for the quality and correctness of you explanation. Feel free to contact me with any questions about the problem set until Noon on Thursday.
lacO^c? ??is an operator mutation that prevents binding of repressor. Consider the following strains:
lacI+? ?lacp+? ?lacOc? ?lacZ?+(? If a gene is not shown in this and any subsequent question, assume it be a wild type allele). Using + and – symbols to indicate ?–galactosidase activity, what will ?–galactosidase activity be when...
...the mutant is grown without lactose? Explain your reasoning.
... the mutant is grown with lactose? Explain your reasoning.
lacI-? ?is a null allele of the lacI gene. Consider the following strain: lacI-? ?lacp+? ?lacO+?lacZ+? ?U? sing + and – symbols to indicate ?–galactosidase activity, what will ?–galactosidase activity be when ...
...the mutant is grown without lactose? Explain your reasoning.
...the mutant is grown with lactose? Explain your reasoning.
Explain how combinatorial control makes it possible to have far fewer transcription factors than the number of genes that are transcriptionally regulated.
If a miRNA were 5 nucleotides long, what is the chance of finding a complementary sequence in a randomly selected 5 nucleotide sequence in mRNA? [Assume mRNA sequences to be random and that mRNAs have an equal amount of each nucleotide (A, U, G, and C)]. If an miRNA were 10 nucleotides long, what is the chance of finding a complementary sequence in a randomly selected 10 nucleotide sequence in mRNA? If
you were designing a synthetic miRNA to specifically target a particular mRNA, would you want to design a 5 or 10 nucleotide long miRNA? Why?
On the basis of the positions of the genes, the enhancer, and the insulator, the transcription of which genes is most likely to be stimulated by the enhancer? Explain your reasoning.
In the fungus Neurospora crassa, roughly 2 – 3% of cytosines are methylated. Researchers isolated Neurospora DNA sequences that contained 5-methyl cytosine and found that almost all methylated sequences were located in inactive copies of transposable elements. On the basis of these observations, propose a possible explanation for why Neurospora methylates its DNA and why DNA methylation in this species is associated with transposable elements.
Some cases of bacterial gene regulation involve use of alternative transcriptional terminators. Propose a plausible way that a riboswitch could function in the use of alternative bacterial transcriptional terminators.
Explanation / Answer
1. Mutant grown without lactose-----Beta galactosidase+ . The operator is mutated, so no repressor can bind. The genes are expressed constitutively. If lactose is not present, and repressor cannot bind , the lacZ gene is expressed.
Mutant grown with lactose------------Beta galactosidase+ . The lactose present inactivates repressor.Any way the lac Z gene is transcribed and gene is expressed.
2. If LacI is null allele, then for mutant grown with lactose ----Beta galactosidase+. The repressor is non fiunctional and hence is not inactivated by the inducer(lactose itself). If repressor is not functional, the transcription goes on .
mutant without lactose-------Beta galactosidase + , The repressor cannot bind to the operator, as the LacI gene is non functional. Hence lac Z gene is constitutively expressed
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