Which of the following statements about hemoglobin and myoglobin structure are true? Select the five true 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.

2. Molecular oxygen binds irreversibly to the Fe(II) atom in heme.

3. Heme is composed of an organic protoporphyrin component and a metal atom.

4. Each hemoglobin molecule can bind four oxygen molecules; each myoglobin can bind only one oxygen molecule.

5. Hemoglobin and myoglobin are heterotetramers.

6. Both hemoglobin and myoglobin contain a prosthetic group called heme, which contains a central iron atom.

7. Each iron atom can form six coordination bonds: One of these bonds is formed between iron and oxygen.