USA Biology Olympiad (USABO) Practice Exam

What can be deduced about the oxygen affinities of hemoglobin and myoglobin?

1. Hemoglobin has greater oxygen affinity than myoglobin

2. Both have equal oxygen affinity

3. Myoglobin has greater oxygen affinity than hemoglobin

4. Hemoglobin binds to carbon dioxide more effectively

The correct answer is: Myoglobin has greater oxygen affinity than hemoglobin

Myoglobin indeed has a greater oxygen affinity than hemoglobin, and this is crucial for understanding the different roles these proteins play in the body. Myoglobin is primarily found in muscle tissues and is specialized for storing oxygen. Its structure allows it to bind oxygen tightly, ensuring an adequate supply during periods of intense muscle activity when oxygen levels might be temporarily low. This high affinity for oxygen means that myoglobin can effectively hold onto oxygen until it’s needed by muscle cells. In contrast, hemoglobin is the protein found in red blood cells and is designed for transporting oxygen from the lungs to various tissues in the body. Hemoglobin's oxygen binding is influenced by various factors, including pH, temperature, and carbon dioxide concentration through a process known as cooperative binding. This means that while hemoglobin's affinity for oxygen is lower than that of myoglobin, it is able to release oxygen more readily in tissues that are actively using it. Understanding the different oxygen binding affinities highlights the adaptive roles of myoglobin and hemoglobin in the body. Myoglobin's strong affinity allows it to store oxygen effectively for high-demand periods, while hemoglobin's variable affinity allows for efficient oxygen transport and release where it is most needed.