Biology questions




1a.Describe one element of the lac operon that is under transcriptional control and one element that is under post-translational control.

b.Discuss how the transcription product of the lac operon, i.e. a single transcript of lacY, lacZ, and lacA, gives rise to 3 different and separate proteins.

2a.You are studying lacI mutants that normally show low expression of the β-galactosidase gene under high glucose levels. However, you get a second mutation where you notice high expression of β-galactosidase in the presence or absence of glucose. Hypothesize where this mutation could be found.

b.Compare and contrast:

i. Basal transcription factors and sigma.

ii.Promoter-proximal elements and enhancers.

3.Rearrangements of the chromosome can often result in the generation of a cancerous cell. During one cancer setting the cells become more responsive to a growth hormone, i.e. they grow uncontrollably when normal amounts of this growth hormone are present. This is due to the overproduction of the receptor for the growth hormone in the cancer cells. You sequence the gene that produces the growth hormone but you cannot find any mutations in the promoter or promoter proximal elements.Based on these data, explain why the growth hormone receptor is overproduced.

4.The trp operon contains 5 genes: trpE, trpD, trpC, trpB, and trpA. These five genes code for components that produce three enzymes that catalyze the biosynthesis of tryptophan. The trp operon undergoes negative repression by a repressor, where in the presence of Tryptophan, the repressor is active and binds to the Trp operator, preventing RNA polymerase from transcribing the operon (See figure attached). You are interested in producing 13C radioactively labeled tryptophan and the easiest way to do this is to grow bacteria on 13C labeled glucose. To maximize the yield of tryptophan you isolate mutant E. coli that overproduce tryptophan.List all possible types of mutations that could have occurred and briefly indicate why they lead to overproduction of tryptophan.

5.You are trying to express human growth hormone in bacteria using a plasmid that has the following DNA sequence elements:Promoter:Lac operator:start codon:codons for growth hormone:stop codon:mRNA termination.You induce the expression of the growth hormone by adding lactose to the media and you get very little growth hormone made.What additional DNA sequence should your plasmid contain and where on the plasmid would you put this sequence.

6a.Predict how gene expression would be affected if a cell is grown in the presence of a compound that inhibits the activity of the enzyme DNA methyl transferase.

b.Mutations in Histone Acetyl Transferases (HAT) that render this enzyme constitutively active are prevalent in many cancer types. Speculate on a mechanism by which these acquired mutations would alter the function of HAT in a cancerous cell.



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