Proteins are one of the most abundant organic molecules in living systems and have an incredibly diverse range of functions. Proteins are used to:
Build structures within the cell (such as the cytoskeleton)
Regulate the production of other proteins by controlling protein synthesis
Slide along the cytoskeleton to cause muscle contraction
Transport molecules across the cell membrane
Speed up chemical reactions (enzymes)
Act as toxins
Each cell in a living system may contain thousands of different proteins, each with a unique function. Their structures, like their functions, vary greatly. They are all, however, polymers of amino acids, arranged in a linear sequence (Figure 1).
The functions of proteins are very diverse because they are made up of are 20 different chemically distinct amino acids that form long chains, and the amino acids can be in any order. The function of the protein is dependent on the protein’s shape. The shape of a protein is determined by the order of the amino acids. Proteins are often hundreds of amino acids long and they can have very complex shapes because there are so many different possible orders for the 20 amino acids!
