Suppose the sequence below is a template DNA sequence. What is...

Question

Suppose the sequence below is a template DNA sequence. What is the corresponding protein sequence?

Accepted Answer

So at first glance, this practice problem might seem exactly identical to our previous practice problem, especially since the sequence of nucleotides it's given is exactly the same from 5 prime to 3 prime. But there's a key difference in this practice problem. And so it says, suppose the sequence below is template DNA sequence, what is the corresponding protein sequence? And so in our last practice problem, the sequence that was given was a coding DNA sequence. But here, we're told that it is a template DNA sequence. And a template DNA sequence is different than a coding DNA sequence, and so that changes our answer entirely. And so recall that the template DNA sequence is complementary and base pairs with the coding DNA sequence. And the way that the base pairing works is that adenines, or a's, pair with thymines, or t's, and cytosines, or c's, pair with guanines, or g's. And so if we want to derive the coding DNA sequence from the template DNA sequence, then all we need to do is apply these base pairing rules. And so let's go ahead and do that down below. So we know that a's pair with t's, t's pair with a's, g's with c's, c's with g's, t's with a's, g's with c's, c's with g's, g's with c's, t's with a's, c's with g's, t's with a's, c's with g's, a's with t's, and g's with c's. And so this sequence here is our coding DNA sequence. So we can label it over here as the coding DNA sequence. Now next, what we're gonna need to recall is that in a DNA molecule that's double stranded, the two strands are antiparallel to one another, meaning that the directions in terms of 5 prime to 3 prime are opposite to one another. And so because the top strand is going from 5 prime to 3 prime from left to right, that means that the bottom strand, the coding DNA sequence on the bottom, must be going from 5 prime to 3 prime in the opposite direction from right to left, meaning that our 5 prime end is on side, and the 3 prime end is over here on this side. And so, we know that we're trying to obtain a protein sequence, and so we're going to need to use the genetic code. And in order to use the genetic code, we need to be reading the mRNA codons, which means that we need to convert the DNA, coding sequence into an mRNA sequence. And recall that the mRNA sequence is exactly the same as the coding DNA sequence, except the fact that all of the t's or thymines are replaced with Us, or uracils, in the mRNA. And also recall that when we use the genetic code, it reads the mRNA from the 5 prime end to the 3 prime end. So we want to rewrite the mRNA sequence so that it's 5 prime to 3 prime from left to right. So essentially, we're going to rewrite our coding DNA sequence exactly, but backwards, and we're going to replace the t's with u's as we go along. So our first nucleotide here is c, and then our next two are, two t's, but we know that t's are replaced with u's. So we've got c u u. The next one is g a g. Then we have a a c. Next is g c a, then we have g g c is next, and then last but not least, we have c a t, but again, the t's are replaced with u's. And so this allows us to have our, mRNA sequence from the 5 prime to the 3 prime end, since, again, we read these, sequence backwards like this. So now that we have our mRNA sequence, we can use a genetic code which reads the mRNA in codons, and codons are sets of 3 nucleotides. So if we break up our mRNA into codons, our first codon is CUU, the next one is GAG, then we have AAC, GCA, GGC, and CAU. And so essentially, each of these amino acid I'm sorry. Each of these codons corresponds to an amino acid, and the way that we reveal the amino acid acid is by using the genetic code that's on the previous page up above. And so, we're not going to go through the process of using the genetic code again, but we just did that in our previous practice problem. So if you don't remember how to do that, make sure you go back and check out our previous practice problem. And so when we use the genetic code, the codon C U U reveals a leucine amino acid residue whose one letter code is l. GAG reveals a glutamic acid residue, aac reveals asparagine, gca reveals alanine, then ggc reveals glycine, and CAU reveals histidine. And so essentially, this here is our protein sequence, and so, because we have the arrow over here, we can put our protein sequence answer over here on this side. And so our protein sequence is just leucine, glutamic acid, asparagine, alanine, glycine, and histidine. And this is from the n terminal end to the c terminal end of the peptide. And so our answer here is this answer right here, and so that concludes this practice problem, and I'll see you guys in our next video.

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Suppose the sequence below is a template DNA sequence. What is the corresponding protein sequence?

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