How many oxygen molecules can haemoglobin bind?

How many oxygen molecules can haemoglobin bind?

• A. Two
• B. One
• C. Four
• D. Three

Answer: (C)

Hemoglobin can bind up to four oxygen molecules because it has four heme groups, one in each subunit, and each heme can bind one O2 molecule. In adult hemoglobin this comes from its four subunits (two alpha and two beta), giving four potential binding sites. The binding process is cooperative, so once one O2 binds, the remaining sites become more likely to bind as well, enabling effective loading in the lungs and release in tissues. The actual amount bound at any moment depends on oxygen partial pressure, but the maximum capacity is four.

Hemoglobin can bind up to four oxygen molecules because it has four heme groups, one in each subunit, and each heme can bind one O2 molecule. In adult hemoglobin this comes from its four subunits (two alpha and two beta), giving four potential binding sites. The binding process is cooperative, so once one O2 binds, the remaining sites become more likely to bind as well, enabling effective loading in the lungs and release in tissues. The actual amount bound at any moment depends on oxygen partial pressure, but the maximum capacity is four.