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question(emergence)--feedback inhibition

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question(emergence)--feedback inhibition

Postby rinchan » Sun Dec 04, 2005 1:31 am

question(emergence)--feedback inhibition

Now i am working on my homework,but it is difficult to me, so I present them here,hoping for your help,3x

1..the amino acids isoleucine and valine share a common patheay for most steps in their biosynthesis.In
Escherichia coli the first common step can be subject to feedback inhibition by valine but not by isoleucine.
In most strains,though ,the addition fo valine does not cause sioleucine deprivation.however,in other strains it does
(tha is, adding valine causes sioleucine starvation and the cells stop growing). What explanation can you give
for the difference between the normal "valine_resistant" strains and those whose growth is sensitive to valine?

2..waht would happen to regulation from a promoter under negative control if the region where the regulatory protein
binds were deleted? what if the promoter were under positive control?

3..Promoter from Escherichia coli under positive control are not close matches to DNAconsensus sequence for E.coli.why?

4..interestingly,the attenuation contrtol of some of the pyrimidine biosynthetic pathway genes in Escherichia coli
actually involves coupled transcription and talation. Can you describe a mechanism whereby the cell could
somehow make use of translation to help it measure the lever of pyrimidine mucelotides?
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Postby GreenDog » Sun Dec 04, 2005 9:15 pm

1. I'm not sure I understand the question but here is what I can say: It depends on the AHAS you have, there are three AHASes, and if I recall right only AHAS2 is valine resistant. Most strains have just 1 and 3 they are sensitive, but several strains have only AHAS2 and thus valine resistant. E-Coli K12 has lost it and they are Val sensitive.
2. In the first case constitutive expression. In the second no expression whatsoever.
3. What?
4. Attenuation is very cool but too long to explain, so either invent a mechanism or read about attenuation. In short though: RNA created during translation can make secondary structures and interact with DNA. In bacteria Translation and transcription are simultaneous. An attenuator region is a region in the beginning of the mRNA, a "protein" is being translated in that region but it has several codons in a row for the amino acid which production it regulates. If the aa is abundant the ribosome runs fast and the mRNA creates a structure called terminator which interferes with DNA and stops transcription. If this aa is not present in the cell the ribosome gets stuck and an antiterminator is created from the RNA.
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