Summary
Highlights
Biological polymers are large macromolecules built from smaller unit molecules called monomers through a modular construction process. These polymers serve various functions, such as providing structure within or outside cells or acting as nutrient storage. Their formation occurs through condensation reactions, which release water, and the individual monomers within a polymer are referred to as residues.
Proteins, also known as polypeptides, are formed from amino acid monomers linked by peptide or amide bonds. There are 20 common amino acids, allowing for a vast variety of protein combinations. Each unique sequence of amino acids results in a specific three-dimensional confirmation, which is crucial for its function.
Nucleic acids are polymers of nucleotides, forming polynucleotides. The nucleotides are connected by phosphodiester bonds, which involve two ester linkages to a central phosphorus atom. With only four types of nucleotides in RNA or DNA, genetic diversity is achieved through the variety of nucleotide combinations rather than the number of types.
Polysaccharides are polymers of monosaccharides, or carbohydrates, linked by glycosidic bonds. An interesting aspect of polysaccharides is that the same monomers can combine in different ways to produce polymers with significantly different structures, such as starch and cellulose, both composed entirely of glucose residues but with distinct properties.
Unlike proteins, nucleic acids, and carbohydrates, lipids do not form larger polymers. This is because they lack a common functional group that allows them to be joined together in a repeating chain. Instead, lipids such as palmitate, sterate, cholesterol, triacylglycerols, and glycerophospholipids aggregate in various ways rather than forming linear polymeric structures.