Red Blood Cell Structure
Red blood cells have a unique structure. Their flexible disc shape helps increase the surface area-to-volume ratio of these extremely small cells. This enables oxygen and carbon dioxide to diffuse across the red blood cell's plasma membrane more readily. Red blood cells contain enormous amounts of a protein called hemoglobin. This iron containing molecule binds oxygen as oxygen molecules enter blood vessels in the lungs. Unlike other cells of the body, mature red blood cells do not contain a nucleus, mitochondria, or ribosomes. The absence of these cell structures leaves room for the hundreds of millions of hemoglobin molecules found in red blood cells.