C. Fourth Level of Protein Structure 1. Hemoglobin consists of four folded chains called globins, each with a heme group. Quaternary structure describes the complexing of two or more polypeptide chains. Keratin and collagen are examples of complex structural proteins. D. Glycoproteins and Lipoproteins 1.
Some proteins have other organic molecules attached to their polypeptide chains.
Lipoproteins and glycoproteins transport lipids and oligosaccharides, respectively. E. Structural Changes by Denaturation 1. High temperatures or chemicals can cause the three-dimensional shape to be disrupted. Normal functioning is lost upon denaturation, which is often irreversible. Nucleotides and Nucleic Acids A. Nucleotides are small organic molecules.