Organisms of all three domains of life usually use the m...

Question

Organisms of all three domains of life usually use the mRNA codon AUG as the start codon.

Despite AUG being the most common start codon sequence, very few proteins have methionine as the first amino acid. Why is this the case?

Accepted Answer

Hello everyone and welcome to today's video. So is often used as the first amino acid in eukaryotic protein synthesis. But there are very few polypeptides that have methionine at the end terminal residue. Because so as answer choice A we have methionine is less stable and often soft, degraded. As answer choice B, we have methionin residue may be cleaned off by other enzymes after translation. And as answer choice C we have both translational modifications that can alter the amino acid sequence at the end terminus. Now let's go over each of our answer choices so that we may solve this problem. As answer choice we have methionine is less stable and often solve degraded. It's going to be incorrect because methionine like any other amino acid is able to form part of the protein structure without the need for soft degradation. This is not true and it does not happen. So we're going to cancel this out. Then we have the methionine residue may be clipped off by other enzymes after translation. So it turns out that many eu proteins have their initial methionine residue removed by enzymes called amino pepsis. Now this this is going to result in a different amino acid at the end terminal residue. This is a process called methionine A. Now moving on because this is a true statement, we're not going to cancel it out. Moving on, we have C which is post translational modifications that can alter the amino acid sequence at the end terminus. So many a proteins also undergo posttranslational modifications. For example, some proteins are asce at the end terminus which can just replace these a, these amino this amino acid, this met with an A group. Now, because of this, we're going to find very few polypeptides with methionine at the end terminal because sometimes it gets replaced by this aceto group due to this post translational modifications. This is also true. So we're not going to cancel it out because we were not able to cancel out either B or C. The correct answer is going to be both B and C. I really hope this helped you and I hope to see you on the next one.

Organisms of all three domains of life usually use the mRNA codon AUG as the start codon.

Despite AUG being the most common start codon sequence, very few proteins have methionine as the first amino acid. Why is this the case?

Key Concepts

Start Codon and Translation Initiation

Post-Translational Modifications

Alternative Start Codons

Watch next

Organisms of all three domains of life usually use the mRNA codon AUG as the start codon.Despite AUG being the most common start codon sequence, very few proteins have methionine as the first amino acid. Why is this the case?

Key Concepts

Start Codon and Translation Initiation

Post-Translational Modifications

Alternative Start Codons

Watch next

Organisms of all three domains of life usually use the mRNA codon AUG as the start codon.

Despite AUG being the most common start codon sequence, very few proteins have methionine as the first amino acid. Why is this the case?