Question

Select all statements that correctly describe hemoglobin and myoglobin structure.

1) By itself, heme is not a good oxygen carrier. It must be part of a larger protein to prevent oxidation of the iron.
2) Molecular oxygen binds reversibly to the Fe(II) atom in heme.
3) Hemoglobin and myoglobin are heterotetramers.
4) The heme prosthetic group is entirely buried within myoglobin.
5) Each iron atom can form six coordination bonds. Two of these bonds are formed between iron and oxygen.
6) Both hemoglobin and myoglobin contain a prosthetic group called heme, which contains a central iron (Fe) atom.
7) Each hemoglobin molecule can bind four oxygen molecules; each myoglobin can bind one oxygen molecule.

Answer 1

Correct statements regarding hemoglobin and myoglobin include their need for being part of a larger protein to carry oxygen, the reversible binding of oxygen to Fe(II), their six coordination bonds' capacity in iron, both containing a heme prosthetic group, and their oxygen-binding capacities, with four for hemoglobin and one for myoglobin.

Step-by-step explanation:

The question asks about characteristics of hemoglobin and myoglobin, specifically their structures and how they bind oxygen. Here are the correct statements:

1. By itself, heme is not a good oxygen carrier. It must be part of a larger protein to prevent oxidation of the iron. This is correct because free heme can lead to oxidation of the iron from Fe(II) to Fe(III), which cannot bind oxygen.
2. Molecular oxygen binds reversibly to the Fe(II) atom in heme. This statement is accurate as the iron atom in heme is indeed in the +2 oxidation state and can bind oxygen reversibly.
3. Each iron atom can form six coordination bonds. Two of these bonds are formed between iron and oxygen when it is present. This statement is true. Four coordination bonds are with the nitrogen atoms of the porphyrin ring, one with the proximal histidine, and the sixth position is available for oxygen binding.
4. Both hemoglobin and myoglobin contain a prosthetic group called heme, which contains a central iron (Fe) atom. This is a correct characterization of both proteins.
5. Each hemoglobin molecule can bind four oxygen molecules; each myoglobin can bind one oxygen molecule. Again, this statement is true. Hemoglobin is a tetramer with four heme groups, while myoglobin is a monomer with a single heme group.

However, the following statements are incorrect:

• Hemoglobin and myoglobin are heterotetramers. This is not true for myoglobin, which is a single polypeptide chain and therefore not a tetramer at all, but it is true for hemoglobin, which is a tetramer.
• The heme prosthetic group is entirely buried within myoglobin. While much of the heme is buried, it is not entirely so, as there is a channel for oxygen to reach the iron atom.