Figure 3.4. Myoglobin molecule.In describing proteins, several descriptive levels of structure have
been defined. What is called the primary structure of the protein is the
linear sequence of amino acids forming the protein—a list of the com-
ponent amino acids in the order they occur in the polypeptide chain.
The secondary structure describes the interactions of nearby amino
acids to produce patterns of local folding within the protein. Nearby
amino acids may interact with one another via hydrogen bonding
and other sorts of electrical attraction and repulsion. This may give
rise to distinct varieties of local folding within the protein. The most
famous example of protein secondary structure is the alpha helix, first
described by the great chemist Linus Pauling (1901-1994). In Figure
3.4, alpha helices are represented by twisted sections of ribbon.
The tertiary structure is the overall shape of the entire protein