Suppose that base substitution mutations sufficient to elimina...

Question

Suppose that base substitution mutations sufficient to eliminate the function of the operator regions listed below were to occur. For each case, describe how transcription or life cycle would be affected.
O_R3 mutation in λ phage

O_R3 mutation in λ phage

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together which genes transcription is positively affected by a mutation in the or three operator site. Among the following the answer options are AC one BC, two, option C Crow and option DN. So we should recognize that all of these answer options are regulatory genes for lambda phage. So for this question, I'd like to look at a drawing of the sequence of these regulatory genes, including the operators and the promoters. And on the screen, I am putting up a drawing of just that. So from left to right, the sequence order is NC one or three or two or one. Crow and C two. Now remember that the promoters overlap the operators. So the PR M promoter overlaps or three and or two while the pr promoter overlaps or two. And or one. In addition, as we talk through this problem together, I'd like to use a key and I am putting that key up on the screen right now. So the C one protein will be represented by an orange circle. Crow is represented by a blue oval and RN A polymerase is represented by a green circle. OK. So the question is about a mutation in the or three operator site. So what role does or three have in lambda phage? Now recall that two molecules combined the operators, either the C one protein or cro. Also recall that C one will preferentially bind to or one and or two. Conversely, crow preferentially binds to or three first. So what happens when crow binds or three? And I am depicting that on the drawing up on the screen. So recall that crow is a repressor. So when crow binds or three, it blocks and represses the Pr M promoter and thus, it would repress any genes that are under the control of the PR M promoter. Now recall the PR M promoter is the promoter for the C one gene which transcribes and produces C one protein. So crow binding or three represses Pr M promoter and thus C one gene transcription. Now, crow binding or three doesn't affect the PR promoter. That means that RN A polymerase can come and bind this promoter which I have depicted on the screen. Now binding of the RN A polymerase to the PR promoter is going to produce further crow. So it will up regulate more crow transcription. So quick summary in a normal pha without any mutation, cro bins or three, ultimately repressing C one protein transcription and allows further crow transcription. So a mutation in the or three operator site, crow will not be able to bind to or three properly. That means the PR M promoter is not repressed or blocked. And thus, you would get transcription of that C one protein and you would also continue to have production of Crow. So RN a polymerase is able to bind to both promoters. But remember, C one protein is normally not transcribed when or three is normal without a mutation. So again, a mutation in or three crow is not able to bind and you get production of more C one protein. So it's the C one protein that is positively affected. And so the correct answer is option ac one. All right, everyone. I hope you found this helpful. I know it's a bit of a longer problem. So feel free to review it and rewatch the video if you need to. But I'll see you soon for the next practice problem.

Suppose that base substitution mutations sufficient to eliminate the function of the operator regions listed below were to occur. For each case, describe how transcription or life cycle would be affected.
O_R3 mutation in λ phage

Key Concepts

Operator Regions

Transcription Regulation

Base Substitution Mutations

Watch next

Suppose that base substitution mutations sufficient to eliminate the function of the operator regions listed below were to occur. For each case, describe how transcription or life cycle would be affected. OR3 mutation in λ phage

Key Concepts

Operator Regions

Transcription Regulation

Base Substitution Mutations

Watch next

Suppose that base substitution mutations sufficient to eliminate the function of the operator regions listed below were to occur. For each case, describe how transcription or life cycle would be affected.
O_R3 mutation in λ phage