Each of the four subunits that make up hemoglobin is arranged in a ring-like fashion, with an iron atom covalently bound to the heme in the center of each subunit. Hemoglobin is composed of subunits, a protein structure that is referred to as a quaternary structure. There are multiple factors involved in how readily heme binds to and dissociates from oxygen, which will be discussed in the subsequent sections.įigure 22.25 Erythrocyte and Hemoglobin Hemoglobin consists of four subunits, each of which contains one molecule of iron. In this formula, Hb represents reduced hemoglobin, that is, hemoglobin that does not have oxygen bound to it. Oxyhemoglobin is a bright red-colored molecule that contributes to the bright red color of oxygenated blood. The following reversible chemical reaction describes the production of the final product, oxyhemoglobin (HbâO 2), which is formed when oxygen binds to hemoglobin. As oxygen diffuses across the respiratory membrane from the alveolus to the capillary, it also diffuses into the red blood cell and is bound by hemoglobin. One hemoglobin molecule contains iron-containing Heme molecules, and because of this, each hemoglobin molecule is capable of carrying up to four molecules of oxygen. Heme is the portion of hemoglobin that contains iron, and it is heme that binds oxygen. Erythrocytes contain a metalloprotein, hemoglobin, which serves to bind oxygen molecules to the erythrocyte ( Figure 22.25). The majority of oxygen molecules are carried from the lungs to the bodyâs tissues by a specialized transport system, which relies on the erythrocyteâthe red blood cell. A small amount of oxygen does dissolve in the blood and is transported in the bloodstream, but it is only about 1.5% of the total amount. ![]() Oxygen Transport in the BloodĮven though oxygen is transported via the blood, you may recall that oxygen is not very soluble in liquids. Although carbon dioxide is more soluble than oxygen in blood, both gases require a specialized transport system for the majority of the gas molecules to be moved between the lungs and other tissues. In order for the exchange of oxygen and carbon dioxide to occur, both gases must be transported between the external and internal respiration sites. The function of respiration is to provide oxygen for use by body cells during cellular respiration and to eliminate carbon dioxide, a waste product of cellular respiration, from the body. ![]() The other major activity in the lungs is the process of respiration, the process of gas exchange. Describe the principles of carbon dioxide transport.Compare and contrast fetal and adult hemoglobin.Describe the principles of oxygen transport.By the end of this section, you will be able to:
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