Proteins
Proteins are the most abundant kind of macromolecule found in the cells of living things. Proteins are composed of linear chains of subunits called amino acids.
Human beings have tens of thousands of different kinds of proteins, and each one has a specific function. Proteins can be grouped into several general classes, including:
- structural proteins, which provide physical support; e.g. collagen
- hormonal proteins, which regulate physiological processes; e.g. insulin
- respiratory proteins, which transport oxygen; e.g. myoglobin
- enzymes, which increase the rate of biochemical reactions; e.g. lysozyme
- DNA binding proteins, which bind to DNA and regulate the expression (transcription) of genes.
- signal transduction proteins, which react to some stimulus (such as light or the presence of a hormone) and pass this signal to other proteins.