In complex IV, what happens once the tightly held oxygen molecule is completely reduced?
AIt is bound permanently to the copper ions
BIt picks up two hydrogen ions to make water
CIt picks up two carbon atoms to make sugar
DIt is pumped out into the intermembrane space
Answer & Solution
Correct answer: B. It picks up two hydrogen ions to make water
1. The cytochromes of the fourth complex hold an oxygen molecule very tightly between iron and copper ions.
2. They keep hold of it until the oxygen is completely reduced.
3. The reduced oxygen then picks up two hydrogen ions from the surrounding medium to make water.
4. Removing those hydrogen ions from the system contributes to the ion gradient used in chemiosmosis.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 7 "Cellular Respiration", section 7.4 Oxidative Phosphorylation_
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