Question

Which of the following is the earliest discovered amino acid?
A. Glycine
B. Methionine
C. Phenylalanine
D. Asparagines

Answer 1

Hint: The first amino acid was discovered in 1806 by the French chemist, Louis-Nicolas Vauquelin and Pierre Jean Robiquet. They isolated the first amino acid from the asparagus.

Complete answer:
Amino acid is an organic compound which contains an amine group ($N{H_2}$ ), carboxyl functional group ($ - COOH$ ), and R group (side chain) specific to each amino acid.
Glycine-Henri Braconnot, a French chemist, in $1820$ discovered Glycine when he had hydrolysed the gelatine with sulphuric acids. However, glycine can be isolated by hydrolysing the protein. It is a sweet, colourless crystalline solid.
Methionine- In $1921$ John Howard Mueller firstly isolated Methionine. It was first isolated from the casein. It is an essential amino acid in humans. In plants and microbes, its biosynthesis belongs to aspartate along with lysine and threonine. It is a sulphur-containing amino acid.
Phenylalanine- It is also an essential amino acid. The first description of Phenylalanine was made in $1879$, by Schulze and Barbieri. He identified a compound found in the yellow lupine seedling. In $1882$ it was first synthesised by phenylacetaldehyde, ammonia and hydrogen cyanide by Erlenmeyer and Lipp.
Asparagines- It was isolated from the asparagus juice in $1806$ by the French chemist, Louis-Nicolas Vauquelin and Pierre Jean Robiquet. It is a non-essential amino acid in humans, it can be synthesised from metabolic pathways intermediated and not necessary for diet.

Therefore, asparagine was the earliest amino acid. So the correct answer is option D.

Note: Asparagines are found in animals and plants.
Plant source – soy, whole grains, nuts, legumes, etc
Animal source – whey, eggs, fish, seafood, lactalbumin, etc
It is used for the biosynthesis of protein.
A reaction between asparagines and reducing sugar in sufficient amounts of heat produces acrylamide in food. These products are generally found in baking products.