How many heme and iron molecules are in one molecule of hemoglobin?

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Multiple Choice

How many heme and iron molecules are in one molecule of hemoglobin?

Hemoglobin is a tetramer, made of four polypeptide subunits, and each subunit contains one heme group. Each heme group holds one iron ion that can bind one molecule of oxygen. So, per hemoglobin molecule there are four heme groups and four iron ions—four heme-iron centers in total that can carry O2. Some might think eight if counting heme and iron separately, but the functional units are the four heme-iron centers, matching the answer.

Hemoglobin is a tetramer, made of four polypeptide subunits, and each subunit contains one heme group. Each heme group holds one iron ion that can bind one molecule of oxygen. So, per hemoglobin molecule there are four heme groups and four iron ions—four heme-iron centers in total that can carry O2. Some might think eight if counting heme and iron separately, but the functional units are the four heme-iron centers, matching the answer.

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