AP Syllabus focus:
‘Aerobic prokaryotes and eukaryotes both use electron transport chains, but differ in terminal electron acceptors and membrane locations.’
Cellular respiration is conserved across life, but prokaryotes and eukaryotes organise it differently. These differences affect where electron transport occurs, which molecules accept electrons at the end, and how ATP synthesis is coupled to membranes.
Core idea: same logic, different cellular architecture
Respiration transfers electrons from reduced carriers to an electron transport chain (ETC), using released energy to build a proton gradient that powers ATP synthase. What changes between domains is the membrane location of these proteins and, often, the terminal electron acceptor.
Practice Questions
FAQ
Many bacteria encode multiple terminal reductases and regulate them by oxygen sensing.
Human mitochondria are specialised for $O_2$ reduction and lack pathways for using nitrate or sulfate as terminal acceptors.
Gram-negative bacteria often build the gradient into the periplasm between inner and outer membranes.
Gram-positive bacteria pump protons to the exterior of a thick cell wall, so the gradient is across the plasma membrane to the outside environment.
No. Many bacteria use different dehydrogenases, quinones, and terminal oxidases/reductases.
The overall function is conserved (electron transfer + proton motive force), but the protein “modules” vary widely.
Alternative acceptors tend to have lower redox potential than $O_2$, so less free energy is released per electron transferred.
Less energy available generally means fewer protons pumped and a smaller ATP yield.
They regulate membrane permeability, ion transporters, and proton pumps to stabilise internal pH and membrane potential.
Some adjust lipid composition or use sodium-ion gradients as partial substitutes in extreme conditions.
