Determine which of the following amino acid pairs could potentially perform hydrogen bonding between their respective r groups.
For option a, we have Glycine and Serine together. Glycine has an H as its R group. Because of the presence of an H, there's no way that it could form hydrogen bonding with its r group with serine. So this is out as a possibility.
Next, we have Aspartic acid and Glutamic acid. These are acidic amino acids. They possess carboxylic acids within their R groups. Because of this, they have the potential to hydrogen bond. So, we say that this could perform hydrogen bonding between their respective R groups.
Next, we have Valine and Leucine. These two represent non-polar amino acids. Their r groups are hydrocarbons. They're only composed of carbons and hydrogens, so they wouldn't be able to engage in hydrogen bonding with their r groups. So this is out.
Then finally, we have Aspartic acid again, and then we have Arginine as our other amino acid. Aspartic acid is an acidic amino acid. Arginine is a basic amino acid. It can exist as a protein as an amino group that has an H already on it, or it can exist in its neutral form. Either way, because one is acidic and one is basic, they could engage in hydrogen bonding between their respective R groups. So this is also a possibility.
In this case, we can say both options B and D could engage in hydrogen bonding between their respective r groups. Right. So the answer again here would be options B and D.