Question

Which of the following statements are correct about $\alpha$-amino acids?

• A. All the amino acids which constitute proteins have D-configuration
• B. Isoelectric point of glycine is $6.1$
• C. Valine is an essential amino acid
• D. In $\alpha$-amino acids, the basic group is $(-CO{O}^{\ominus })$ and acidic group is $(-\stackrel{\oplus }{N}{H}_3)$

Answer 1

Answer: (B), (C), (D)

The statements (B), (C) and (D) are correct about $\alpha$-amino acids.

(A) The amino acids which constitute proteins have mostly L-configuration.

(B) Isoelectric point of glycine is $6.1$. The isoelectric point (pI), is the pH at which a particular molecule carries no net electrical charge.
Glycine has pKa $=$ 2.72, 9.60
$pI=\frac{2.72+9.60}{2}=6.1$

(C) Valine is an essential amino acid as it cannot be synthesised in body. Leucine, isolucine, lysine, phenyl alanine are some examples of essential amino acids.

(D) In $\alpha$-amino acids, the basic group is $(-CO{O}^{\ominus })$ and acidic group is $(-\stackrel{\oplus }{N}{H}_3)$. $\alpha$-amino acids exists in the form of zwitter ions in which carboxylic group is deprotonated and amino group is deprotonated.