During the formation of the peptide bond which of the following takes place?

Hydroxyl group is lost from its carboxyl group of one amino acid and a hydrogen atom is lost from its amino group of another amino acid

The correct answer is option 4. Hydroxyl group is lost from its carboxyl group of one amino acid and a hydrogen atom is lost from its amino group of another amino acid.

Peptide bonds are formed between amino acids during protein synthesis through a dehydration synthesis reaction. 

Amino acids have a central carbon atom (alpha carbon) bonded to a hydrogen atom, an amino group \((-NH_2)\), a carboxyl group \((-COOH)\), and a side chain (\(R\) group).  During peptide bond formation, the carboxyl group \((-COOH)\) of one amino acid reacts with the amino group \((-NH_2)\) of another amino acid. Specifically, the hydroxyl group \((-OH)\) from the carboxyl group of one amino acid and a hydrogen atom (H) from the amino group of another amino acid are released as a water molecule \((H_2O)\).

The carbon atom of the carboxyl group \((C=O)\) undergoes nucleophilic attack by the lone pair of electrons on the nitrogen atom of the amino group. This results in the formation of a peptide bond \((C-N)\) between the carbonyl carbon of one amino acid and the nitrogen of the other amino acid.

The peptide bond \((-CO-NH-)\) is a planar structure with partial double bond character due to resonance stabilization. The amino acids linked by the peptide bond form a dipeptide, and this process can continue to form longer polypeptide chains.

Example:

 Why Option 4 is Correct: Hydroxyl group is lost from its carboxyl group of one amino acid and a hydrogen atom is lost from its amino group of another amino acid. This option correctly describes the dehydration synthesis process where the components of water (\(H\) from \(-NH_2\) and \(OH\) from \(-COOH\)) are removed during peptide bond formation. This dehydration reaction leads to the formation of the peptide bond between the amino acids.

Conclusion: The process of peptide bond formation involves the loss of water (dehydration synthesis) between the carboxyl group of one amino acid and the amino group of another amino acid. This explanation aligns with option 4, making it the correct answer.