Final answer:
Ubiquinone and cytochrome c are mobile electron carriers within the electron transport chain, facilitating electron transfer between complexes. The ATP yield in cellular respiration varies due to factors like electron shuttle type and oxygen availability, affecting the number of ATP molecules produced.
Step-by-step explanation:
The roles of ubiquinone and cytochrome c in the electron transport chain (ETC) are distinct from the other components because they serve as mobile electron carriers. Ubiquinone, also known as coenzyme Q, and cytochrome c shuttle electrons between the various enzyme complexes located within the inner mitochondrial membrane. This movement of electrons through carriers with differing redox potential facilitates the conversion of energy into an electrochemical gradient, which is then used by the enzyme ATP synthase to generate ATP through oxidative phosphorylation.
The ATP yield from cellular respiration is influenced by numerous factors. One key factor is the type of electron shuttle used in transporting electrons from glycolysis into the mitochondria. For instance, using NAD+ as the transporter, as in liver cells, would generally yield more ATP compared to using FAD, as in brain cells, because FADH2 contributes its electrons further down the electron transport chain which is associated with the production of less ATP compared to NADH. Additionally, oxygen availability is crucial as it is the final electron acceptor in the chain, and its absence can prevent the ETC from functioning, thus limiting ATP production.