Is the bond formed between each pair in Problem 18.76 covalent...

Question

Is the bond formed between each pair in Problem 18.76 covalent or noncovalent?

a. Cysteine and cysteine

b. Alanine and leucine

c. Aspartic acid and asparagine

d. Serine and lysine

Accepted Answer

All right. Hi, everyone. So this question says for each of the following pairs of amino acids indicate whether the bond formed between their side chains is covalent or non covalent. For part one, we have lysine and gamine. Part two is asparagine and thine. Part three is Sistine and Sistine and part four is vain and pheno ay. And here we have four different answer choices labeled A through D proposing whether or not each pair is covalent or non covalent. Now recall that of all of the side chain interactions present in amino acids that you study, we can classify them as either covalent or non covalent. Now, in the context of proteins and of amino acid side chain interactions, the only covalent interaction present here is the formation of the disulfide bridge. And recall that the disulfide bridge is a bond formed between two residues of cysteine abbreviated as cys because recall that cysteine contains a th or an sh group in its side chain. So two thy groups can interact and create a covalent bond between both sulfur atoms. Now, on the other hand, on the non covalent side, these interactions are more or more. So attractive forces in between the side chains. These include ionic interactions involving side chains that have a charge to them hydrophobic interactions involving side chains that are non polar and lastly hydrogen bonding or H bonding. For short, now recall that H bonding is possible when you have a neutral amino acid side chain that contains either a hydroxy or oh group or an NH two group because the requirement for H bonding is a hydrogen atom bound to a highly electron element such as oxygen nitrogen or fluorine. So now that we have a better sense of what these terms mean, I want to go ahead and consider the structures of all of the pairs discussed here. And as you can see towards the bottom of the screen, I went ahead and I actually drew these amino acids separately. So now that I've scrolled down, you can see parts one and two on the screen here. One being on the left side and two being on the right side. So let's go ahead and get started with the structures of lysine and glutamine. For part one, lysine is on top and glutamine is on the bottom. So the first thing I want to point out here is that lysine has a side chain that has a charge to it specifically in the nitrogen. Here at the very end of the side chain glutamine. On the other hand, is actually neutral. So what that means is that lysine and glutamine would not participate in any sort of ionic interaction with each other. But regardless, both lysine and glutamine have these amino groups in their structures, meaning they both have nitrogen and we have hydrogen connecting to a highly electron element such as nitrogen. So all this is to say that lysine and glutamine, even though they cannot participate in ionic interactions because one has a charge and the other does not, they can participate in H bond, which as discussed before is an example of a non covalent interaction. So part one or the first pair is non covalent. So up next on the right side, for part two are asparagine on top and three anne on the bottom. So here we have a very similar scenario to the first pair of lysine and glutamine because it just so happens that asparagine and thine are both neutral or rather that they contain neutral side chains. However, espero gene contains an amino group in the side chain and thine contains a hydroxy or oh group. So in both cases, for both asparagine and threatening we have a hydrogen attached to a highly electron element that's nitrogen and oxygen respectively. So, asparagine is and three anine, you can participate in bonding as well, which is a non covalent interaction. Now let's move on to part three. Part three involves two cysteine residues. So I did not draw Sistine twice. I only drew Sistine once but recall why Sistine is important to us it's because of this s group at the very end of its side chain referred to as a file. Now, when two cysteine residues combine together, they can create a covalent bond between both sulfur atoms. Meaning that the two cysteine residues for part three are going to form a disulfide bridge or disulfide bond, which is in fact coiling and last but not least we have part four, which is or R vein on the top and pheno alanine on the bottom. Now let's go ahead and talk about these side chains. The side chain of valle is a simple hydrocarbon otherwise referred to as an al kill group. On the other hand, the side chain of pheno alanine contains what's called a benzoyl group. Because in addition to the benzene ring, we have an additional carbon atom outside of the ring connecting to the alpha carbon of the amino acid. Now, both the ocho group and the benzoyl group are examples of hydrocarbon chains because they're only composed of hydrogen and carbon. Recall that hydrocarbon chains are characteristically nonpolar because there's no significant difference in electronegativity between carbon and hydrogen. So therefore, both of these amino acids veen and pheno alanine contain nonpolar hydrophobic side change. So they participate in hydrophobic interactions, which as discussed previously are in fact, non covalent and there you have it. So just to recap what we've been talking about up to this point, we've discussed so far four different pairs of amino acids. Now, all of them are actually participating in non COVID interactions except for pair three, because the two cysteine residues for part three are the only ones that participate in a covalent disulfide bond. So if I scroll up here to the very beginning, our answer is going to be option B in the multiple choice because pair one is non covalent two is non covalent three is covalent and four is non covalent. So if you stuck around until the end of this video, thank you so very much for watching. And I hope you found this helpful.

Is the bond formed between each pair in Problem 18.76 covalent or noncovalent?
a. Cysteine and cysteine
b. Alanine and leucine
c. Aspartic acid and asparagine
d. Serine and lysine

Key Concepts

Covalent Bonds

Noncovalent Interactions

Bond Polarity

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