If glutamate were replaced by proline in a protein, how might the tertiary structure be affected?

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Accepted Answer

All right. Hello everyone. So this question is asking us if all sine is replaced with leucine in a protein, what would you expect from the protein's tertiary structure? Now, here we have four different entry choices labeled A through D which we'll discuss individually later on in this video. For now, I just want to go ahead and provide some context as to what change is happening here in the first place, right? Recall first and foremost that the tertiary structure of a protein refers simply to the three dimensional structure of that polypeptide chain, right? And that three dimensional structure is achieved through various interactions between the side chains of amino acids. And so because amino acid side chains tend to have different properties because of their different polarities, there are many different types of interactions that contribute to the tertiary structure of protein. So with this in mind, our first or rather our original protein you could say is sine. Now Cine, if you recall is considered to be a polder, neutral amino acid because it is neutral at physiological ph but it's polar because it has a hydroxy group in the side chain. This is in contrast now to lucine. So now Cine has been replaced with lucine, which if you recall is a nonpolar amino acid because of its hydrocarbon side chain. So not only has the amino acid changed, but the polarity of the side chain is also changing, which means that the interactions that are going to take place between those side chains are of course going to be different. And so now that we've talked a little bit more about what's happening in this problem. Let's analyze our answer choices individually. Starting with option A, it says that the protein might become more soluble in water. Now, this is not going to be true, right? Because the new amino acid leucine is nonpolar and hydrophobic. If anything, it's going to reduce the solubility of the protein in water. Option B says that the protein stability might increase due to new hydrophobic interactions. This could be true, right? Because now the new residues of leucine that are in the protein can engage in hydrophobic interactions with each other and provide an extra layer of stabilization of a tertiary structure. So that's good. So now let's move on to option C which says that the protein might lose flexibility due to the introduction of a rigid structure. Now this answer choice can be a little misleading but I do want to point out that it's not correct because when we talk about the rigidity of the structure, right? When we're talking about the rigid structure of a protein. We're talking about the backbone of the protein. We're talking about the multiple peptide bonds that hold that polypeptide chain intact. That's the rigid structure. The interactions between amino acid side chains are not considered part of the rigid structure. So this question is incorrect or this choice is incorrect. Last but not least though we have option D which says the protein's overall shape might not change. This is not true, right? Because as mentioned before the interactions that are going to take place between these lucid side chains are going to be different compared to those of searing. So different interactions opens the possibility to the protein folding differently and resulting in a different structure to the main point here is that our answer is going to be option B in the multiple choice and there you have it. So with that being said, thank you so very much for watching and I hope you found this helpful.

If glutamate were replaced by proline in a protein, how might the tertiary structure be affected?

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Key Concepts

Amino Acid Properties

Tertiary Structure of Proteins

Protein Folding and Stability