Question

Using DNA sequencing on a cloned DNA segment, you recover the nucleotide sequence shown below. Does this segment contain a palindromic recognition sequence for a restriction enzyme? If so, what is the double-stranded sequence of the palindrome, and what enzyme would cut at this sequence? (Consult Figure 20.1 for a list of restriction sites.)

CAGTATGGATCCCAT

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next question. It says a palindrome IQ recognition sequence for a restriction enzyme is a sequence of nucleotides. That is the same when read in either direction, which of the following sequences is a palindrome IQ sequence. So let's recall that a restriction enzyme recognizes a specific DNA sequence, double stranded DNA sequence and cuts that sequence in a specific pattern and its not directional like say when you add bases onto a growing nucleotide strand, it can be recognizing the D N A approaching its recognition sequence from either side. And that's why that sequence needs to be palindrome IQ that it recognizes. So let's look through the answer choices looking for the palindrome sequence. I'm going to write them out as two strands, one on top of the other to make it just a little easier to recognize. So first we'll start with choice A and I will write them like that. Well, when we look at the D N A sequence made by these two strands, we can see not only is it not palindrome IQ, it's not the same read forwards and backwards. Um It's not even properly complementary, it wouldn't occur as a DNA double strand. So we can go ahead and eliminate that. You can see here, we've got G paired with T right away. Um So that's choice A is not the correct answer. So now let's look at Choice B and write that out as one strand on top of the other. And now when we look at these two strands, um not only are they not the same forwards and backwards here, C G A, their G T A, there are the same um top and bottom. But of course, that makes an incorrect strand as the top strand and bottom strand should not be, should not be the same but should be complimentary base pairs. So you wouldn't have see, wanted to see that should be a C with a G complementary to it. So again, this D N A strand wouldn't even exist as part of a double helix and therefore, is not our answer. So let's move on to choice. See, but when we look at this, these two DNA sequences, we see we are properly complementary, the matching czar correct on the top and bottom strand. And when we read from either side, so looking at the top strand, we have G A T T C, then when we read the other strangle in the other direction G A T T C. So this is a palindrome D N A sequence on both strands. So that is our answer choice here. Choice C. So now it's just for the sake of being thorough. Look down at choice D. When we look at this sequence, we see it is properly complimentary, all the bases are properly matched. But when you try and read it from side to side, you C C G T A T G and then if you try and read the other direction on the bottom strand, you get C A T already, it's different. So this is not a palindrome IQ, although it is a possible D N A sequence, so that's why choice D is not correct. So again, which of the following sequence is a palindrome IQ sequence that could be recognized by restriction enzyme. And that's choice. C see you in the next video.

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