Question 18, Bio/Biochem, Practice Test 3 (2018)

[mirandalola]

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Please help me understand why two isoforms of a protein are produced by a single mRNA transcribed from a single promoter sequence upstream of the operon. I'm looking this up in wikipedia and I can't understand why it's not 2 different mRNAs.

 

[Cornfed101]

So in the passage it states that the two genes are under control of the operon or something along those lines. What I did was that made me cue into the lac opening structure. The whole thing is one mRNA strand but has different sections which have different fxns. The promotion, regulator etc but the actual genes are also on this single strand. The way these are transcribed are through different start and stop sections so it’ll be something like this: start—gene A—stop—start—gene B—stop. Check out a picture of the lac operon if my explanation wasn’t helpful maybe you can understand it by visualizing it