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Chemistry Question 70 – JEE-MAIN 2025

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Identify the correct statement among the following :

Recall the general structure of amino acids and the definition of a chiral center.

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Ninja Strategy•Systematic Evaluation of Amino Acid Properties

Carefully recall the structural and chemical properties of common amino acids, paying attention to exceptions and specific functional groups to identify the single correct statement.

● Video Walkthrough
Step 1: Evaluate Statement 1: Chiral Centers✦ Active

Glycine does not have a chiral center. Most other standard amino acids have one chiral alpha carbon. However, amino acids like Threonine and Isoleucine possess two chiral centers (the alpha carbon and a beta carbon). Therefore, the statement that all naturally occurring amino acids except glycine contain *one* chiral center is incorrect.

Step 2: Evaluate Statement 2: Optical Activity○ Expand

Optical activity requires the presence of a chiral center. Since glycine lacks a chiral center, it is not optically active. Thus, the statement that all naturally occurring amino acids are optically active is incorrect.

Step 3: Evaluate Statement 3 & 4: Specific Amino Acid Properties○ Expand

Cysteine contains a thiol (−SH) group in its side chain. This group can be easily oxidized to form a disulfide bond (−S−S−), leading to the dimerization of two cysteine molecules to form cystine. This statement is correct. Regarding glutamic acid, while it does contain a −COOH group in its side chain, it is not the *only* amino acid with this feature; aspartic acid also has a −COOH group in its side chain. Therefore, statement 4 is incorrect.

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