Which of the following mutations, occurring just after the start codon in the mRNA is likely to have the most serious effects on the polypeptide product?

Okay, everyone. Which of the following mutations occurring just after the start codon in the mRNA is likely to have the most serious effect on the polypeptide product. Okay. So we're talking about different types of mutations and which one is the most dangerous, the most serious to the function of the protein that is being made. We're talking about mutations in the mRNA. So let's have a look at our answer choices. Answer choice a says the deletion of 1 codon. Well, if 1 codon is deleted, then that means 1 amino acid is being deleted. And in the grand scheme of things, most proteins are thousands of amino acids, so the deletion of 1 amino acid probably isn't that of a deal. So this is probably not the answer we're looking for. Answer choice b says the deletion of 1 nucleotide. You may think that this doesn't sound like a big deal, but, actually it is. Think about all the codons in a sequence, and they all code for a very specific amino acid for that protein to function. If you delete 1 nucleotide or insert 1 nucleotide, then all of the codons following that mutation have now changed because all of the nucleotides have shifted in position by one because either one nucleotide was deleted in this case or one nucleotide was added. Now all of the codons following that mutation have changed. This is called a frameshift mutation, and it is very dangerous. It's gonna change almost all of the amino acids after the mutation, so a lot of this protein could be nonfunctional. So this is a great answer. Let's rule out the other 2. Answer choice c says the insertion of 3 nucleotides. Well, you're just adding another codon, which means you're just adding an extra amino acid. As long as this particular insertion of 3 nucleotides does not code for a stop codon, you're probably fine. So this is not gonna be the answer we're looking for. Answer choice d says, substitution of 1 nucleotide. Well, this could substitute one nucleotide for another, and maybe it changes the codon, but maybe it doesn't change the amino acid. Remember that some codons are redundant, so that wouldn't matter at all. The amino acids wouldn't change. Or let's say it does change the codon, which does change the amino acid. Again, in the grand scheme of things, it's only 1 amino acid changing, not all of them. So this one's probably fine. So the most dangerous, most serious type of mutation that we can see here in our list of answer choices is the deletion of 1 nucleotide, which would lead to a frameshift mutation, which could possibly disrupt a lot of the protein's structure. Okay, everyone. Let's move on to our next video.

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Which of the following mutations, occurring just after the start codon in the mRNA is likely to have the most serious effects on the polypeptide product?

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