From the Guidelines
The false statement about hemoglobin is "Hemoglobin only binds oxygen." This is incorrect because hemoglobin can bind several molecules besides oxygen, including carbon dioxide, carbon monoxide, nitric oxide, and hydrogen ions, as discussed in the context of carbon monoxide poisoning 1. While oxygen transport is hemoglobin's primary function, its ability to bind other molecules is crucial in understanding various physiological and pathological processes. Hemoglobin does contain four protein subunits (two alpha and two beta chains), and each subunit contains a heme group with an iron atom at its center that can bind oxygen. The statement about increasing affinity is also true and describes the cooperative binding property of hemoglobin - as one oxygen molecule binds, it causes conformational changes that increase the affinity of the remaining binding sites for oxygen (positive cooperativity) 1. This property allows hemoglobin to efficiently pick up oxygen in the lungs and release it in tissues where oxygen concentration is lower. The binding of carbon monoxide to hemoglobin, forming carboxyhemoglobin, is particularly noteworthy due to its high affinity for hemoglobin, approximately 220 times that of oxygen, leading to tissue hypoxia and other toxic effects 1.
Key points about hemoglobin and its binding properties include:
- Hemoglobin's structure includes four subunits, each with a heme group capable of binding oxygen and other molecules.
- The binding of oxygen to hemoglobin exhibits positive cooperativity, increasing the affinity for oxygen as more oxygen molecules bind.
- Hemoglobin can bind molecules other than oxygen, such as carbon monoxide, which has significant implications for understanding carbon monoxide poisoning and its treatment 1.
- The management of carbon monoxide poisoning involves the use of oxygen therapy to decrease the elimination half-life of carboxyhemoglobin and mitigate tissue hypoxia and other toxic effects 1.
From the Research
Hemoglobin Characteristics
- Hemoglobin is a complex molecule with multiple subunits, each containing a heme group with an iron atom 2
- Hemoglobin contains four subunits, which work together to bind and transport oxygen 2
- Hemoglobin can bind oxygen, but it also has other functions and can interact with other molecules 2
Oxygen Binding and Affinity
- As O2 molecules bind to hemoglobin, the affinity of hemoglobin for O2 can change, but the statement that affinity increases is an oversimplification 2
- The binding of oxygen to hemoglobin is a complex process, influenced by various factors, including allosteric effectors and the structure of the hemoglobin molecule 2
False Statement
- The statement "Hemoglobin only binds oxygen" is false, as hemoglobin has other functions and interactions beyond oxygen binding 2
- The other options, "Every subunit of hemoglobin contains a heme group with an iron atom", "Hemoglobin contains four subunits", and "As O2 molecules bind to hemoglobin, hemoglobin affinity for O2 increases" are not entirely accurate or are oversimplifications, but "Hemoglobin only binds oxygen" is the most clearly false statement 2