Proteins
Proteins have many different functions in living things. Enzymes are a type of protein.
Antibodiesthat protect your body from disease are proteins, and your muscles are made of
protein. All proteins are made of monomers (small building block molecules) called amino
acids that line up to form long chains. There are only 20 common amino acids. These amino
acids have the general chemical formula H 2 NCHRCOOH, where R is a ”side group” which
varies between amino acids. It is this side group that gives the amino acids its physical
and chemical properties. These amino acids form in thousands of different combinations,
generating up to 100,000 unique proteins. Proteins can differ in both the number and order
of amino acids. Small proteins have just a few hundred amino acids, whereas the largest
proteins have over 25,000 amino acids.
Figure 2.10: General Structure of Amino Acids. This model shows the general structure
of all amino acids. Only the side chain, R, varies from one amino acid to another. For
example, in the amino acid glycine, the side chain is simply hydrogen (H). In glutamic acid,
in contrast, the side chain is CH 2 CH 2 COOH. Variable side chains give amino acids acids
different chemical properties. The order of amino acids, together with the properties of the
amino acids, determines the shape of the protein, and the shape of the protein determines
the function of the protein. KEY: H = hydrogen, N = nitrogen, C = carbon, O = oxygen,
R = variable side chain ( 29 )
After a cell makes a protein chain, the chain folds into a 3-dimensional structure (Figure
2.11). Proteins fold based on the sequence and properties of the amino acids. The properties
of amino acids can vary widely, so the position of each amino acid in a protein is important.
Each folded protein has its own unique shape. It is this shape that gives the protein its
function. The primary structure of a protein is the linear sequence of amino acids. The