Question #0a09e

1 Answer
Mar 25, 2017

Answer:

Methionine is a nonpolar amino acid because it has a nonpolar side-chain.

Explanation:

We usually write the general structure of an amino acid as #"H"_2"NCHRCOOH"#.

However, the #"H"_2"N"# end is basic, while the #"COOH"# end is acidic.

The molecule therefore exists as a "zwitterion", #"H"_3stackrel("+")("N")"CHRCOO"^"-"#.

Thus, it usually has a charge at one end or the other and is a polar species.

However, the term polar amino acid usually refers to the side-chains that will impart a more polar character to the amino acid.

Side chains with functional groups such as acids, amides, alcohols, and amines do impart a more polar character to an amino acid. They form polar amino acids.

The structure of methionine is

o.quizlet.com

We see that the #"-CH"_2"CH"_2"-S-CH"_3# side-chain contains only nonpolar #"C-C, C-H"#, and #"C-S"# bonds.

Thus, methionine is a nonpolar amino acid.