How are amino acids linked together by condensation to form polypeptides?

Sourav PanNovember 8, 2024

Answered

Amino acids are linked together through a process known as condensation (or dehydration synthesis) to form polypeptides. This process involves the formation of peptide bonds, which are specific types of covalent bonds that link amino acids together in a chain. Here’s how this process occurs:

1. Structure of Amino Acids

Each amino acid has a central carbon atom (the alpha carbon) bonded to four groups:

• An amino group (-NH₂)
• A carboxyl group (-COOH)
• A hydrogen atom (-H)
• A variable side chain (R group), which determines the identity and properties of the amino acid.

2. Mechanism of Peptide Bond Formation

Condensation Reaction

The formation of a peptide bond occurs through a condensation reaction, which can be summarized in the following steps:

1. Approach of Amino Acids: Two amino acids come close together, positioning their functional groups for interaction. The carboxyl group of one amino acid aligns with the amino group of another.
2. Removal of Water:
   • The hydroxyl group (–OH) from the carboxyl group of the first amino acid and a hydrogen atom (–H) from the amino group of the second amino acid are removed.
   • This removal results in the formation of a water molecule (H₂O).
3. Formation of Peptide Bond:
   • The remaining parts of the two amino acids are now linked by a covalent bond known as a peptide bond (–CO–NH–). This bond is an amide linkage formed between the carbon atom of the carboxyl group and the nitrogen atom of the amino group.
   • The resulting molecule is called a dipeptide if it consists of two amino acids.

General Reaction

The overall reaction can be represented as:

3. Polypeptide Formation

• As more amino acids undergo condensation reactions, they continue to link together, forming longer chains called polypeptides.
• A polypeptide can consist of many amino acids (typically more than 50), and once it folds into a specific three-dimensional structure, it can function as a protein.

4. Role of Enzymes

In biological systems, peptide bond formation is catalyzed by enzymes known as ribosomes during protein synthesis. These enzymes facilitate the condensation reaction, ensuring that it occurs efficiently and correctly in living organisms.