In addition to a solid introduction to myoglobin, this brief but excellent discussion also includes an explanation of the dissociation constant and fractional saturation, two quantities for describing protein binding. These concepts are figures of merit for the MCAT.

This is a great article. The sections on Fe/heme binding and subsequent binding of dioxygen are challenging. Although these sections are more advanced than prerequisite content for the MCAT, they represesnt a good reading exercise.