Making life possible: Proteins

Without proteins, living things wouldn’t exist. Many proteins provide structure to cells; others bind to and carry important molecules throughout the body. Some proteins are involved in reactions in the body when they serve as enzymes (see Chapter 4 for more on enzymes). Still others are involved in muscle contraction or immune responses. The building blocks of proteins could be referred as follows:

Amino acids, of which there are 20, are the foundation of all proteins. Think of them as train cars that make up an entire train called a protein. Figure 3-4 shows what one amino acid looks like.

The genetic information in cells calls for amino acids to link together in a certain order, forming chains called polypeptide chains. Amino acids link together by dehydration synthesis, just like sugars do, and each polypeptide chain is made up of a unique number and order of amino acids.