Draw and explain the structure of an amino acid. Explain how it is possible for proteins to vary extensively when there are only 20 naturally occurring amino acids and what determines this variety. What is a peptide? What is a polypeptide? Explain the functions of proteins in the cell and include an example of each type. A. Structural B. Storage C. Transport D. Defensive E. Enzymes F. Movement G. Receptors Describe the different levels of protein structure in detail. Explain denaturation and list things that can cause it.