3.5: Dehydration Synthesis
Dehydration synthesis (also called a condensation reaction) is the chemical process in which two molecules covalently link together to form a new molecule, along with the release of a water molecule. Many physiologically important compounds form by dehydration synthesis reactions, such as complex carbohydrates, proteins, DNA, and RNA.
Synthesis of carbohydrates
Sugar molecules are covalently linked together by dehydration synthesis. During the reaction, the hydroxyl (-OH) group from one reactant combines with the hydrogen atom of the other to form water, while the remaining oxygen links the two compounds by a glycosidic bond. Individual glucose molecules (monomers) can undergo repeated dehydration synthesis to create a long chain or a branched-chain structure known as a polymer.
Synthesis of peptides and polypeptides
A peptide bond (CO-NH) is a chemical bond produced by attaching the carboxyl group of one amino acid to the amino group of another, forming a peptide chain. Since a water molecule is released to form a peptide bond, the process is referred to as dehydration synthesis. This process continues during translation as amino acids join continuously to the preceding one by peptide bonds, forming a polypeptide chain.
Synthesis of lipids
Lipids such as triglycerides are composed of one glycerol and three fatty acids. The three hydroxyl groups of the glycerol molecule and the carboxyl groups of three fatty acids interact to form ester bonds with the removal of three water molecules. This process is referred to as dehydration synthesis of lipids.
Synthesis of nucleic acids
Nucleic acids are synthesized by the polymerization of nucleotide monomers with the formation of a phosphodiester bond between two consecutive nucleotides. As water molecules are removed during their polymerization, the process is known as dehydration synthesis.