The accompanying illustration shows a portion of a gene ...

Question

The accompanying illustration shows a portion of a gene undergoing transcription. The template and coding strands for the gene are labeled, and a segment of DNA sequence is given. For this gene segment:

Superimpose a drawing of RNA polymerase as it nears the end of transcription of the DNA sequence.

Accepted Answer

Hi, everyone. Welcome back. Here's our next problem. It says during transcription, only one of the DNA strands is used as a template for R N A synthesis. While the other strand is not transcribed, the strand of DNA being transcribed is called choice A template and coding strand, choice B template and noncoding strand, choice C coding or send strand and choice D template and send strand. So let's just think through the different strands in this process of transcription. I'm just going to write a little sample short DNA bit in blue, we'll say G G A T and so underneath, I'll write it's complementary strand which would be C C T A. So that will be my double stranded DNA that's being transcribed. So I'm going to say that the top strand is the one that's going to be our template for R N A synthesis. So I'm going to rewrite G G A T and now in red underneath, I'll write the R N A strand that is transcribed. So that would be complimentary. So C C and then it's R N A. So instead of A T being complimentary to this A I have a U and then an A. So there's our R N A strand. So we can see that our R N A strand is going to have the same sequence as the strand that is not transcribed, except for obviously the replacement of T in the DNA strand with U in the R N A strand, but to mark that bottom strand as not transcribed. So even though that strand is not transcribed, we sometimes describe it as the coding or since strand. Because if we wanted to know what the sequence of the R N A strand is, we could look at that non transcribed strand to see the sequence of bases. But that's not the one that's transcribed, the other one, the top one G G A T is the template. So let's look through our answer choices with that in mind reminding ourselves that we're looking for the name of the strand that is being transcribed. So I'm gonna circle that top template strand. So choice says template and coding strands. So template is correct. It's a template strand but it is not the coding strand because the coding strand is the name given to the non transcribed strand since it has the same sequence. So we eliminate choice A choice B says template and noncoding strand. Well, this is correct. It's the template strand and it's also the non coding strand since it's the complementary sequence to our M R N A. So choice B is going to be correct. But we'll just keep looking at our other answer. Choices, choice C says coding or sense strand. But again, we know those are names for the non transcribed strand since it does have that same base sequence as the R N A strand. So choice C is not correct. And then finally choice D template and sense strand. So template is correct, but sense is not correct as a name for that transcribed strand. So we rule out choice D. So again, when we're looking for the name of the strand of DNA being transcribed, we're looking for choice B template and noncoding strand. See you in the next video.

My Courses

Chemistry

Biology

Math

Physics

Business

Social Sciences

Programming

Product & Marketing