Biomacromolecular structures

Biomacromolecules are large biological polymers, such as nucleic acids, proteins and carbohydrates, that are made up of monomers linked together.

For example, proteins are composed of monomers called amino acids. They are linked together to form a polypeptide chain, which folds into a three dimensional (3D) structure to constitute a functional protein (Figure 1).  Often a functional macromolecule is composed of more than one such chain and  sometimes requires small molecules to assist in its function.

An image of the amino acid sequence (monomers) and the corresponding 3D structure of ribosomal protein L2

Figure 1 The amino acid sequence (monomers) on the left and the corresponding 3D structure of ribosomal protein L2.

Although this course concentrates on the structural properties of biomacromolecules, it will also cover smaller molecules such as coenzyme, cofactor, prosthetic group, lipid, drug and metal ion because they might interact with and affect these biomacromolecules at the structural level.


When a small molecule binds specifically and reversibly to the biomacromolecule to form a complex and alters its activity or function it is called a ligand (Figure 2).

An example of a complex of a biomacromolecule with a ligand

Figure 2 Example of a complex of a biomacromolecule with a ligand: the structure of human lysozyme. The ligand is a sugar molecule (NAG: N-Acetyl-D-Glucosamine) and is represented by red and blue spheres.

Now let's have a closer look at the different biomacromolecules (DNA, RNA and proteins) and some of the molecules they can interact with.