Chapter 5 Section 3: Protein Structure, after p. 191:
Topic Name: Protein Secondary Structure, at the University of Virginia
There are four levels of protein structure. The primary structure of a protein is the linear order, or sequence, of amino acids. The primary structure dictates the 3-dimensional shape of a protein, and the linked amino acids are further organized into regularly repeating 3-dimensional patterns. These repeating patterns constitute the secondary structure of a protein. The tertiary structure is the biologically active 3-dimensional shape of the entire protein or polypeptide. What are the two types of protein secondary structures called?