A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O). This is a dehydration synthesis reaction (also known as a condensation reaction), and usually occurs between amino acids.

Understanding Peptide Bonds
Peptide bonds are crucial in the formation of proteins, connecting amino acids together through a specific chemical reaction.
What is a Peptide Bond?
- A peptide bond is a covalent bond that links the carboxyl group of one amino acid to the amino group of another.
- This bond is fundamental in the structure of proteins, forming polypeptide chains.
Process of Formation: Dehydration Synthesis
- The formation of a peptide bond occurs through a process known as dehydration synthesis (or condensation reaction).
Mechanism of Dehydration Reaction:
- During this reaction, a molecule of water (H₂O) is removed.
- The carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH₂) of another.
Steps Involved:
1. Activation: The amino acids are activated for the reaction.
2. Condensation: The -OH from the carboxyl group of one amino acid combines with an -H from the amino group of the other.
3. Water Release: This combination releases a water molecule, leading to the formation of the peptide bond (-CO-NH-).
Importance of Dehydration in Biology:
- Dehydration synthesis is not only essential for peptide bond formation but also plays a vital role in the synthesis of carbohydrates and nucleic acids.
- It is a key process in building larger biological macromolecules from smaller units.
In summary, the correct answer is option 'D' (Dehydration) because peptide bonds are formed through the removal of water during the condensation of amino acids. This process is integral to protein synthesis and overall biological function.

By removal of water i.e. dehydration