Consider the following portion of mRNA produced by the normal ...

Question

Consider the following portion of mRNA produced by the normal order of DNA nucleotides:

5'CUU|AAA|CGA|GUU3'

e. What happens to the protein sequence if an A is added to the beginning of the chain and the sequence changes to 5'ACU|UAA|ACG|AGU3'?

Accepted Answer

All right. Hello everyone. So this question is asking us to consider the given MRN a sequence. What is the effect of adding you to the beginning of the chain and changing the protein sequence to become? And here the new Mrna sequences given option A says the protein function is unchanged. B says the protein may have a completely different function. C says the protein will be shorter due to an early stop code on. And de says the protein will not be synthesized. So here on the screen, I went ahead and wrote out both the original and new Mrne sequences. And the reason for this is because I want to go ahead and translate these MRN a sequence sequences, excuse me into amino acid sequences. And then I want to compare them. I want to compare how different the results are. So for this question, we're going to have to translate each code on which if we recall is a triplet of MRN a nucleotides into the corresponding amino acid. Or if if, if it's a start or stop code on and we do so using the genetic code table. So referencing now the original strand and again, referencing our genetic code table. Our first code on is GG A which corresponds to glycine or GLY as is the three letter abbreviation. Our second code on again in the original sequence is UUC which corresponds to phenylalanine. So that's phe from there we have CC which corresponds to Prolene. So that's Pr O and then we have our final code on here in the original sequence UG A which is a stop code on and thats the end of the sequence. All right. So here's our original. So now let's compare this to the new MRN A sequence, but we're, we're still using the genetic code. So for our new sequence, the first code on is UGG which corresponds to trip fan. So that's TP our second coon is a UU which is isoleucine. So it's ile from there, we have CCC which is proline once again. So it's Pr O and then a UG codes for methane. But recall that it is actually a start coda in MRN A. So first of all, what happened, right, what was the main change that resulted in this different MRN a sequence? And therefore amino acid sequence? Well, here the addition of the U in the new Mrna strand completely changes the reading frame of the strand itself. Why? Because this U nucleotide was added to the beginning of the chain, but it wasn't replacing a nucleotide that was already present rather it was being added. And because it was being added, the way that the, the nucleotides themselves are divided into codons changes completely. So the reading frame is completely different. And as you'll notice the following nucleotides, in other words, the nucleotides after the U that's been added match with the original sequence. Because after the U for example, we have GG A which is the first coon of the original sequence. So here we can see that the reading frame and therefore the way that this MRN A sequence is translated has changed completely. So first of all right, the reading frame has been changed. That's one major difference. And the second major difference is at the very end of each respective sequence. Because going back now to the original MRNA strand, notice how the last codon resulted in a stop signal which would stop the translation of this protein at a certain point. On the other hand, going now to the new Mrna strand, the new amino acid sequence that stop code on at the end is actually now a start signal. So what that means is that translation won't stop when it's supposed to. So that's another change, right? Translation won't stop at least when it's supposed to on the original strand. And so what happens as a result of this? Well, if the modified sequence doesn't have a stop code on in the same position as before translation will continue. And if translation continues, and the product of translation, this new modified protein is going to look different from the original. So at the very least, the resulting protein is going to have a completely different function. If vital regions of the protein are affected too much, then the new protein may be completely nonfunctional. So there you have it based on this information, our answer is going to be option B in the multiple choice because the protein may have a completely different function. And so with that being said, thank you so very much for watching. And I hope you found this helpful.

Consider the following portion of mRNA produced by the normal order of DNA nucleotides:
5'CUU|AAA|CGA|GUU3'
e. What happens to the protein sequence if an A is added to the beginning of the chain and the sequence changes to 5'ACU|UAA|ACG|AGU3'?

Key Concepts

mRNA Translation

Codon Changes and Protein Structure

Frameshift Mutation

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