A)Ubiquinone is a small, hydrophobic protein containing a metal group that acts as an electron carrier. B)A 2Fe2S iron-sulfur center carries one electron, whereas a 4Fe4S iron-sulfur center carries two electrons. C)Iron-sulfur centers generally have a higher redox potential than do cytochromes. D)Mitochondrial electron carriers with the highest redox potential generally contain copper ions and/or heme groups.