Hemoglobin's distinct binding sites for respiratory gases

Steps:

• Identify hemoglobin's structure: It has four heme groups with iron for gas binding and globin chains with amino groups.
• Recall oxygen binding: O2 attaches to the iron in heme groups.
• Note carbon monoxide binding: CO also binds to the same iron site in heme, competing with O2.
• Determine carbon dioxide binding: CO2 binds to amino groups on globin chains, forming carbaminohemoglobin, not at heme.

Why B is correct:

• CO and O2 both bind to the heme iron site, while CO2 binds to globin amino groups, as per hemoglobin's molecular structure.

Why the others are wrong:

• A: CO2 and CO do not share a site; CO binds heme, CO2 binds globin.
• C: CO2 and O2 do not share a site; O2 binds heme, CO2 binds globin.
• D: CO and O2 share the heme site, so not all bind different sites.

Final answer: B