#Question id: 4099
#XL - Q Biochemistry
Five E. coli strains have been identified, each of which has a different mutation that disrupts the normal regulation of a particular operon. For each mutant strain, the mutation has been mapped to the promoter or the operator region; however, the exact sequence changes are not known for these mutations. It is known that the normal promoter/operator consists of a single binding site for a positively acting transcription factor located just upstream of the promoter itself. Short DNA fragments containing the promoter and the operator were subcloned from each of the five mutant strains and from the wild type, purified, and radiolabeled. These fragments were then incubated under conditions of DNA excess with either purified regulatory factor or RNA polymerase or with both polymerase and regulatory factor.
The resulting protein-DNA complexes were separated by electrophoresis, and the radioactive DNA fragments were detected by exposure to x-ray film, giving the results shown below. Electrophoresis is from top to bottom; the largest complexes run slowest.
Based on above experiment, match the following
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Effect |
Mutant |
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1. One of the mutations increases the affinity of the polymerase for the promoter. Transcription of the operon is not stimulated by the regulatory factor in this mutant. |
A. Mutant 5 |
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2. One of the mutations maps to the operator. Transcription of the operon is not stimulated by the regulatory factor in this mutant. Which mutant is most likely to show this effect |
B. Mutant 2 |
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3. One of the mutations is known to result from a small deletion between the operator and the promoter. The polymerase and the regulatory factor is each able to bind to the mutated DNA sequence, but are unable to form the three components complex. Transcription of the operon is not stimulated by the regulatory factor in this mutant. Which mutant shows the properties that might be expected for such a change? |
C. Mutant 4 |
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D. Mutant 3 |
|
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E. Mutant 1 |
#Question id: 1670
#XL - Q Biochemistry
The T-cell receptor genes were originally identified using:
#Question id: 4805
#XL - T Zoology
What is maximum parental frequency for two genes if single cross over within two strands?
#Question id: 12734
#XL - S Microbiology
#Question id: 4103
#XL - Q Biochemistry
In a biochemical experiment, you compare the products from splicing reactions carried out in vitro using three different substrates. In each case the substrate is a construct containing a single intron surrounded by two exons, and in all cases the construct is the same overall size. But in one case, the intron is a group I intron, in another a group II intron, and in the third an intron removed by the spliceosome. Each construct is labelled in a manner that allows it to be detected after gel electrophoresis, and each is tested in two reactions—one, conditions that support self-splicing, and two, in the presence of nuclear extract as well. Note that, for simplification, only the final products of the splicing reaction are seen, but before degradation of the introns.
Which of the following observation is/are correct?
A. In lane A, the presence of nuclear abstract, a band for the lariat and the spliced product and pre-mRNA.
B. Lane B shows Group I Introns and Lane C is for Group II introns and reaction is nonself-splicing
C. Lane C is Group I intron. Splicing takes place in the absence and presence of nuclear abstract, and the reaction is self-splicing.