Is phenylalanine hydrophilic or hydrophobic? Explain why.

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Accepted Answer

All right. Hi, everyone. So this question is asking us to identify whether histadine is hydrophilic or hydrophobic. So to understand this question, recall that all amino acids have the same general structure to them. We've got an alpha carbon in the center that attaches to both an amino group and a carboxy grip, but also attached to the alpha carbon is an R group or a side chain. And the side chain is important to us because it is what allows us to distinguish between different amino acids because all amino acids have a different side chain associated to them. And so it is the identity of the side chain that can help us to distinguish whether or not an amino acid is hydrophobic or hydrophilic. Now recall that a substance is said to be hydrophobic if it is insoluble in water, right, it does not dissolve in water. So in the context of analyzing amino acids, amino acids that are hydrophobic, contain nonpolar r groups or side chains. On the other hand, a substance is said to be hydrophilic if it is soluble in water. So in the context of amino acids, amino acids that contain neutro polar acidic or basic side chains are going to be soluble in water and therefore considered hydrophilic. So to understand whether or not histidine specifically is hydrophilic or hydrophobic, we have to recall what histidine actually looks like. So histidine like any other amino acid has the same general structure in which we have an alpha carbon attaching to both a carboxy group and an amino group. But the or group or the side chain of histidine is one additional carbon branching off of the alpha carbon and a unique ring structure. It is a five member ring structure with two nitrogen atoms embedded inside of the ring. Now recall that these nitrogen atoms are significant because they contain a long pair of electrons on each of them. And the lone pairs of electrons on nitrogen means that nitrogen can accept hydrogen atoms or protons, which means that the presence of nitrogen in the side chain of histidine makes histadine basic. And so amino acids with basic side chains are hydrophilic because they do in fact dissolve in water. This means that our answer here is that histidine is in fact hydrophilic and there you have it. So with that being said, thank you so very much for watching. And I hope you found this helpful.

Is phenylalanine hydrophilic or hydrophobic? Explain why.

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Key Concepts

Hydrophilicity and Hydrophobicity

Amino Acid Structure

Phenylalanine's Chemical Properties