Amide Linkage Synthesis in Polypeptides
Dehydration Synthesis in Biological Systems
This process describes the formation of a covalent bond between two molecules through the elimination of a water molecule. It is fundamental to the construction of numerous biological macromolecules.
Amino Acid Structure and Reactivity
Amino acids, the building blocks of proteins, possess an amino group (-NH2) and a carboxyl group (-COOH) attached to a central carbon atom. These functional groups participate in linkage formation.
Mechanism of Amide Formation in Proteins
The carboxyl group of one amino acid reacts with the amino group of another. The oxygen atom from the carboxyl group and two hydrogen atoms (one from the amino group and one from the carboxyl group) are released as water. The remaining carbon atom from the carboxyl group forms a covalent bond with the nitrogen atom from the amino group. This specific type of amide bond is referred to as a peptide link.
Characteristics of the Resulting Bond
The resultant bond exhibits partial double-bond character due to resonance, restricting rotation and conferring a planar geometry to the amide linkage and adjacent atoms. This rigidity is crucial for protein secondary structure.
Role of Ribosomes in Polypeptide Synthesis
Ribosomes facilitate the formation of these linkages during protein synthesis. Transfer RNAs (tRNAs) deliver activated amino acids to the ribosome, where the process is catalyzed, leading to polypeptide chain elongation.
Energy Considerations
The formation of this linkage is an endergonic process, requiring energy input. This energy is typically derived from the hydrolysis of high-energy phosphate bonds, such as those found in ATP.