Question

Which of the following statements is FALSE? Which of the following statements is FALSE? Myoglobin is a single polypeptide chain folded about a heme prosthetic group. Hemoglobin is a tetramer, each of which binds a heme group. In both hemoglobin and myoglobin, iron is chelated by a tetrapyrole ring system. The iron in both hemoglobin and myoglobin has two coordination sites that bind to oxygen.

Answer 1

The false statement is that the iron in both hemoglobin and myoglobin has two coordination sites that bind to oxygen. Myoglobin has one vacant coordination site for O₂, not two, and in hemoglobin, each of the four iron atoms also has one binding site for oxygen.

Step-by-step explanation:

The statement "The iron in both hemoglobin and myoglobin has two coordination sites that bind to oxygen" is the FALSE statement. In myoglobin, the heme iron is five-coordinate, meaning it has a single histidine imidazole ligand from the protein and the four nitrogen atoms of the porphyrin to bind, leaving one vacant coordination site for O₂ to bind. In contrast, while hemoglobin is a tetramer and each subunit binds a heme group, the iron at the center of these heme groups does not have two oxygen binding sites, but rather one like in myoglobin.

Myoglobin is a single polypeptide chain that includes a heme prosthetic group, and hemoglobin consists of four polypeptide chains (two alpha and two beta units), each binding a heme group. Both proteins have iron chelated by a tetrapyrole ring system, which is a fundamental component of the heme group that allows these proteins to bind oxygen and function in oxygen transport or storage.

Answer 2

That would be D(the last one).

Iron in both hemoglobin and myoglobin has 1 coordination site that bind to O2.

Each iron chelated in a tetrapyrrole/porphyrin ring can bind to one oxygen molecule. That is why we say hemoglobin can carry a maximum number of 4 O2 molecules. (See attached pic)