Is the heme group conjugated? The T state of hemoglobin has lower affinity for O

Question

Is the heme group conjugated? The T state of hemoglobin has lower affinity for O2 than the R state because the Fe–Nporphyrin bonds are longer? The iron in the heme group can form six bonds: The fifth is with an imidazole ring of a histidine and the sixth is with oxygen? A heme group contains four pyrrole rings, which are linked via methene (methine) bridges? The cooperativity of oxygen binding in hemoglobin arises from electronic interactions between heme groups? Does hemogloblin really contain 4 heme groups? The globin chains of myoglobin and hemoglobin prevent the oxidation of Fe2 to Fe3 , which irreversibly binds oxygen? true or false for thses questions.

Explanation / Answer

1. Is heme group conjugated? True

2. The T state of hemoglobin has lower affinity for O2 than the R state because the Fe–Nporphyrin bonds are longer. False, when O2 binds, R state is more stable, so hemoglobin undergoes a conformational change to the R state.

3. The iron in the heme group can form six bonds: The fifth is with an imidazole ring of a histidine and the sixth is with oxygen- True, The two additional binding sites are one on either side of the heme plane. One of these is occupied by the imidazole group of His. The second site can be reversibly occupied by O 2, which is hydrogen-bonded to another His.

4. A heme group contains four pyrrole rings, which are linked via methene (methine) bridges. True, The heme group consists of the planar aromatic protoporphyrin made up of four pyrrole rings linked by methane bridges.

5. The cooperativity of oxygen binding in hemoglobin arises from electronic interactions between heme groups? Does hemogloblin really contain 4 heme groups. True,  Inter-subunit interactions influence O2 binding to all 4 subunits resulting in cooperativity.

6. The globin chains of myoglobin and hemoglobin prevent the oxidation of Fe2 to Fe3 , which irreversibly binds oxygen. False, these proteins need to bind O2 reversibly and the Fe(II) heme, by itself, cannot do this. When there is no globin to protect the heme, it reacts with oxygen to form an oxidized Fe(III) atom instead of an Fe(II)-O2 complex.

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