Monomers are small, repeating molecular units that act as the fundamental building blocks for larger, more complex structures called polymers. Polymers are formed when many monomers link together in long chains. This process is a fundamental chemical reaction that underpins the structure of many biological molecules.
The Core Reaction for Polymer Formation
The chemical reaction that links monomers to form polymers is called dehydration synthesis, also known as a condensation reaction. This name describes the process: “dehydration” signifies the removal of a water molecule, and “synthesis” indicates the creation of a new, larger molecule.
During dehydration synthesis, a covalent bond forms between two monomers. This bond formation is accompanied by the release of a water molecule as a byproduct. This reaction is a fundamental mechanism in biology, allowing living organisms to construct the complex macromolecules necessary for life.
The Process of Joining Monomers
Dehydration synthesis involves the removal of atoms from reacting monomers to form water. One monomer contributes a hydrogen atom (H) from one of its functional groups, while the other monomer contributes a hydroxyl group (OH). These two components combine to form a molecule of water (H₂O).
The removal of these groups creates an open bonding site on each monomer. These sites allow the two monomers to link together through a covalent bond. As more monomers are added, this process repeats, extending the polymer chain with each new bond formed and water molecule released.
Examples in Biological Molecules
Dehydration synthesis is central to the formation of many biological polymers. For instance, carbohydrates like starch, glycogen, and cellulose are formed when glucose monomers link together. These polysaccharides serve various roles, from energy storage in plants and animals to structural support in plant cell walls.
Proteins, another class of macromolecules, are also assembled via this reaction. Amino acids, the monomer units of proteins, join by dehydration synthesis to form long chains called polypeptides. Each bond between amino acids is a peptide bond. Similarly, nucleic acids, such as DNA and RNA, are polymers of nucleotide monomers. Dehydration synthesis links these nucleotides to form the sugar-phosphate backbone of the DNA and RNA strands, which carry genetic information.
The Reverse Process: Breaking Down Polymers
The reverse of dehydration synthesis is a reaction called hydrolysis. The term “hydrolysis” means “to split water.” In hydrolysis, a water molecule is added across a covalent bond within a polymer, causing the bond to break and releasing the individual monomer units.
During this reaction, the water molecule splits, with a hydrogen atom (H) attaching to one of the separated monomers and a hydroxyl group (OH) attaching to the other. This process is essential for digestion, allowing the body to break down large food molecules into smaller monomers that can be absorbed and utilized. Hydrolysis also plays a role in the recycling of biological molecules within cells.