[Campbell Biology P.997] How many oxygen molecules can a single hemoglobin molecule bind, an... | Practice Question

How many oxygen molecules can a single hemoglobin molecule bind, and what mechanism facilitates its efficient loading and unloading?

  • A: Two; facilitated by competitive binding with CO2.
  • B: Four; facilitated by cooperativity among its subunits.
  • C: One; due to its single heme group.
  • D: Eight; enabled by a strong, irreversible bond.

Explanation

A hemoglobin molecule has four subunits, each with a heme group containing an iron atom. Each iron atom can bind one O2 molecule, so a hemoglobin molecule can carry four O2 molecules. The binding and release of O2 are enhanced by cooperativity: when O2 binds to one subunit, the others change shape, increasing their affinity for O2, and vice versa for unloading.