Question 11 of 24 In E coli three structural Deand enzymes A

Question 11 of 24 In E. coli, three structural Deand enzymes A. D, and E, respectively. Gene ois an operator. The genes are in the order O-A-D-E on the chromosome and might form an operon. These the the osynthesis of valine. Mutations were isolated at the A, D, E, and o genes to production of cellular A. Adel be enzymes by partial-diploid E. coli with various combinations of mutations are shown in the following table. The wild type is indicated with a and the mutant is indicated with a What type of regulator protein is binding to the operator in this possible operon? Amount of enzyme produced Genotype E D A O an activator O 240 3.50 O a coactivator 2.00 E* D* A* O l O a repressor E* 35.80 38.60 46.80 o an inducer D* A* O O an attenuator 1.00 47.00 D+ A- O D* A Orl Et 35.30 38.00 1.70 E D At 2.38 38.00 47.70 Are genes A, D, and E all under control of the operator o? o Yes, because when the operator is functional the genes E. D. and A expression levels are high. Previous Check Answer 0 Next d Exit

Solution

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Part 1: Choice 4 (the present operon is an inducer type becuase presence of the genetic sequence upstream the operator up-regulates gene expression of the cistron by modultion of transcription of operator gene. This suggests that positive regulation of operator and cistron take place when the up-stream regulator is switched \"on\", hence it is an inducer type operon)

Part 2: Choice 1 (The genes A,D and E are indeed under the transcriptional control of gene O. This is because when levels of gene O are high enough even under heterozygous condition, the expression levels of all these three up-stream regulators are also very high. It must be carefully observed from the dataset that absence of any of the gene A, D or E leads to down-regulation of their expression even when O is dominant/heterozygous. This clearly deciphers the transcriptional co-regulation of this cistron.)