Question

Which of the following is the example of an acidic amino acid?
A. Lysine
B. Glutamic acid
C. Aspartic acid
D. Both B and C

Answer 1

Amino acids are organic compounds. It contains a carboxyl functional group and an amine group, along with a side chain which is specific to each amino acid. The main elements of an amino acid are hydrogen, carbon, oxygen and nitrogen, and other elements that are found in the side chain of amino acid.

Complete answer: Amino acid contains an amino group and a carboxylic group which is attached to the same carbon. The amino acids differ in the type of side chain which is attached to the alpha carbon. Amino acids can be classified into various groups by the type of side chain, concerning its polarity or tendency to interact with water at a particular pH. The polarity of the amino acids side chain varies widely from hydrophobic and nonpolar to highly polar and hydrophilic.
a) Glutamic acid: It is also called as glutamate or acido glutamico. It belongs to the class of organic compounds known as derivatives of glutamic acid. It is an acidic amino acid. It contains amino two acid groups and one amine group.
b) Aspartic acid: It is an alpha-amino acid which is used in the biosynthesis of proteins. Like other amino acids, it has an amino group and a carboxylic acid. The aspartic acid alpha-amino group is in the protonated form. Aspartic acid has an acidic side chain.
c) Lysine: It is an essential amino acid that has a positively charged epsilon amino group. Lysine is highly reactive and is often involved in reactions with active centres of enzymes. The side chain of lysine has three methylene groups.
Hence the correct answer is option D.

Note: Amino acids can also be classified into four groups:
1. Polar side-chain amino acids: Examples are tryptophan, glycine, alanine, methionine, leucine, isoleucine, valine, and proline.
2. Uncharged polar side amino acid: Examples are tyrosine, glutamine, asparagine, cysteine, threonine, and serine.
3. Polar side-chain amino acid (positively charged R group): Examples are lysine, arginine, and histidine.
4. Negatively charged polar side chain: Examples are glutamic acid and aspartic acid.