A bacterial inducible operon, similar to the lac operon, contains three genes—R, T, and S—that are involved in coordinated regulation of transcription. One of these genes is an operator region, one is a regulatory protein, and the third produces a structural enzyme. In the table below, '+' indicates that the structural enzyme is synthesized and '−' indicates that it is not produced. Use the information provided to determine which gene is the operator, which produces the regulatory protein, and which produces the enzyme.

Question

A bacterial inducible operon, similar to the lac operon, contains three genes—R, T, and S—that are involved in coordinated regulation of transcription. One of these genes is an operator region, one is a regulatory protein, and the third produces a structural enzyme. In the table below, '+' indicates that the structural enzyme is synthesized and '−' indicates that it is not produced. Use the information provided to determine which gene is the operator, which produces the regulatory protein, and which produces the enzyme.

Table displaying genotypes and enzyme synthesis in response to an inducer, indicating synthesis presence or absence.

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next problem. Suppose a microbiologist has created three partial diploid strains of E coli each with different genotypes for the LAC operon genes. The researcher wants to determine whether the synthesis of LAC Z M R N A is constitutive or inducible in each strain and whether the strain is able to utilize lactose as a carbon source. Then we have listed the genotypes of the three different strains. Each has two sets of values since these are partial diploid strains for the LAC operon genes. So in strain one, the first set of alls is cap negative but positive or wild type for the genes IP O N Z in the second set of values, they are wild type for all five of those genes and stream two. The first set of values are wild type for all five. The second set has a P negative. So a mutation in the promoter gene and wild type for the other four. And then finally, in strain three, the first set of alls is negative for lax Z and wild type for the other four. While the second set of values is wild type for all five which the above strains is inducible in the presence of lactose. A strain one B, strain two C, strain three or D. All options are correct. Well, what is it that makes the la operon inducible? Well, that means that its default state is off. So we'll say default equals off because of the lac repressor. That lac repressor protein is bound to the operator which blocks the promoter site preventing R N A polymerase from coming in. When it's inducible, it means that it is turned or turns on in the presence of lactose, that's as opposed to constituted expression where a gene has a constant level of expression, no matter what the conditions around it. So how does that lac operon turn on the presence of lactose while the alo lactose, which is that isomer of lactose that some of the lactose is converted into BS to the lac repressor causing it to detach from the operator with the lac repressor out of the way R N A and polymerase can move in and transcribe the lac genes. So what we need to be able to be inducible is we need the gene or the lac repressor to be functional and that gene is the lack I gene. So let's look back at our strains and we see in strain one, we have actually two functional alleys for I. So that would be inducible. So I'll put a little check mark by it in strain two, we also have two wild type allys for the lac igene. So that's also inducible and finally strain three, two wild type eye alleys. So all three strains are inducible in the presence of lactose due to having a functional lack I gene. So the repressor protein will be intact. So choice d all options are correct is the answer that we are looking for to this problem. See you in the next video.

Verified video answer for a similar problem:

Key Concepts

Operon Structure

Regulatory Proteins

Inducible Systems