Question

Which of the following statement is not correct?

• A. Only \(\alpha\)-amino acids are obtained on hydrolysis of proteins
• B. The amino acids which are synthesized in the body are known as non-essential amino acids
• C. There are 20 essential amino acids
• D. L-amino acids are represented by writing the \(-NH_2\) group on the left side

Hint:

Total amino acids in proteins = 20
Essential amino acids = fewer than 20 (dietary requirement)
L-configuration is determined using Fischer projection Do not confuse \emph{total} amino acids with \emph{essential} amino acids.

Answer 1

The Correct Option is C

Step 1: Analyse option (A). Proteins are polymers of \(\alpha\)-amino acids linked by peptide bonds. On hydrolysis, proteins yield only \(\alpha\)-amino acids. \[ \Rightarrow \text{Statement (A) is correct.} \]
Step 2: Analyse option (B). Amino acids that can be synthesized by the human body are called non-essential amino acids. \[ \Rightarrow \text{Statement (B) is correct.} \]
Step 3: Analyse option (C). Although there are 20 common amino acids found in proteins, all of them are not essential. Essential amino acids are those that \emph{cannot} be synthesized by the body and must be obtained from diet. Their number is much less than 20. \[ \Rightarrow \text{Statement (C) is incorrect.} \]
Step 4: Analyse option (D). In Fischer projection:
L-amino acids have the \(-NH_2\) group on the left side
D-amino acids have the \(-NH_2\) group on the right side \[ \Rightarrow \text{Statement (D) is correct.} \]
Hence, the incorrect statement is \[ \boxed{\text{(C) There are 20 essential amino acids}} \]