Final answer:
Cytochrome c shuttles electrons between complex III and complex IV in the electron transport chain. It is not the final protein in the chain, nor does it involve cysteines covalently binding to a heme group when becoming reduced.
Step-by-step explanation:
Which of the following statements about cytochrome c is true? The correct statement is that cytochrome c shuttles electrons between complex III (cytochrome c reductase or cytochrome bc1 complex) and complex IV of the electron transport chain, not between NADH dehydrogenase complex and cytochrome c reductase complex as erroneously stated in option (a).
When cytochrome c becomes reduced, it is the iron within the heme group that transitions from Fe3+ to Fe2+; the cysteines are not covalently bound to the heme group, as stated in option (b). Furthermore, the pair of electrons are not added to the porphyrin ring directly; they are transferred to the iron atom in the heme group which fluctuates between oxidation states based on electron transfer. Therefore, statement (c) is also incorrect.
The last statement (d) suggests that cytochrome c is the final protein in the electron-transport chain, which is not accurate. Instead, electrons are transferred from cytochrome c to complex IV (cytochrome oxidase), which then reduces molecular oxygen to water. Hence, the accurate role of cytochrome c is as an electron carrier within the electron transport chain, which is crucial during the process of cellular respiration.