Proteins are one of the most influential macromolecules, and almost all aspects of life involve their use. Proteins are able to carry out specified cellular functions; some catalyze chemical reactions needed to maintain life while others are used for signaling or to coordinate internal cell activities or inter-cellular communication. Proteins are able to form large organic molecules because they are polymers, which are large molecules made up of repeated subunits. Proteins form these linear polymers by combining 20 different amino acids, each with unique chemical characteristics.

The sequences of these amino acids that make up the protein are stored in the DNA  located in the nucleus. The DNA is transcribed into RNA, and translated into proteins. The sequence of bases in RNA determines the order of successive amino acids that will result in new proteins. The formation of proteins occur within the ribosomes, which are large complexes of RNA and protein molecules. The sequence of amino acids in a protein is known as the primary structure that determine how the protein will fold. The interactions between those primary structures form local secondary structures, when the secondary structures interact they form the overall three-dimensional shape or its tertiary structure. These tertiary structures are called polypeptides, some proteins are a combination of these polypeptides forming quaternary structures.

These macromolecules play a vital role in immune defense, energy storage, and structure creation. They can also be used as enzymes to catalyze or speed up chemical reactions. Each enzyme recognizes one or more substrates to catabolize, synthesize, or rearrange their substrates. They can also send messages within cells and across the body. Examples include hormones such as insulin and glucagon that coordinate different body systems. Furthermore, they transport oxygen across the body through hemoglobin. Proteins allow for the wide range functions of life to maintain homeostasis and can become infinitely complex and add to life’s diversity.