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The classification of the following amino acids according to theirstructuresas nonpolar, polar, acidic, or basic.
Introduction:
Amino acids are the basic unit of a protein. The chain of an amino acid is calledpolypeptide. Each amino acid has a carboxylic end and an amino end. One amino acid is linked to another via a peptide bond. There are 20 amino acids that are found naturally in our body and are known as standard amino acids.
Explanation of Solution
The amino acids can be classified as polar, nonpolar, acidic, and basic. The nonpolar amino acids have hydrocarbonscontaining R group (side chain), and they lack any type of charge. The polar amino acids have a polar hydroxyl group (-OH). The -SH group (sulfhydryl group) is also polar in nature. The acidic amino acids have R chain containing carboxylate group (-COOH), while the basic amino acid has an amino group in the side chain.
The structure (a) in the given question is the amino acid, cysteine. It has a polar group of -SH in its R-chain (side chain). Thus, it is a polar amino acid.
The structure (b) in the given question is the amino acid, phenylalanine. It has a nonpolar group:a benzene ring, as its side chain, which bear no positive or negative charges. Thus, it is a nonpolar amino acid.
The structure (c) in the given question is the amino acid, lysine. The amino group is present in the R-chain, which bears positive charge at physiological pH, which is basic in nature. Thus, it is a basic amino acid.
The structure (d) in the given question is the amino acid, glutamate. It has a carboxylic group as the R-chain, which bears negative charge at physiological pH, which is acidic in nature.
Therefore, it can be concluded that the given structures are classified as
a) Polar (cysteine)
b) Nonpolar (phenylalanine)
c) Basic (lysine)
d)Acidic (glutamate)
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Chapter 5 Solutions
Biochemistry: The Molecular Basis of Life
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