Summary
Protein complexes in the inner mitochondrial membrane pass electrons to oxygen while pumping protons.
In depth
Complexes I to IV pass electrons from NADH and FADH2 to O2, pumping protons (about 10 H+ per NADH) across the inner membrane. Oxygen is the final acceptor, producing water. Ubiquinone and cytochrome c are mobile carriers.
Complexes I, III and IV pump protons; II doesn't. Electrons pass from lower to higher electronegativity. Final transfer to oxygen forms water.
Example: rotenone inhibits Complex I.
The electron transport chain (ETC) is a series of protein complexes (I to IV) and mobile carriers (ubiquinone and cytochrome c) embedded in the inner mitochondrial membrane. NADH and FADH2 donate electrons, which pass step by step to lower energy levels and finally to oxygen, forming water.
The energy released pumps protons from the matrix into the intermembrane space at complexes I, III and IV, building a gradient. Poisons such as cyanide (blocks complex IV) and carbon monoxide halt the chain and cause rapid death, while rotenone blocks complex I. Bacteria have a similar chain in their plasma membranes.
Example: oxygen is needed only as the final electron acceptor.
Key idea: the chain itself makes no ATP; it builds the gradient that does.
Frequently asked questions
What is Electron Transport Chain?
Protein complexes in the inner mitochondrial membrane pass electrons to oxygen while pumping protons.
Which area of biology covers Electron Transport Chain, and how advanced is it?
Electron Transport Chain is one of the 53 topics in Metabolism & Bioenergetics. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Light Reactions and ATP Synthesis, Oxidative Phosphorylation, Chemiosmosis.
Can you give an example of Electron Transport Chain?
Cyanide and carbon monoxide block complex IV.
What should I learn before Electron Transport Chain?
Work through the Beginner topics in Metabolism & Bioenergetics first, such as Metabolism, Anabolism and Catabolism, ATP, then return to Electron Transport Chain. Intermediate topics assume the Beginner vocabulary.
What topics are related to Electron Transport Chain?
The closest topics to Electron Transport Chain are Light Reactions and ATP Synthesis, Oxidative Phosphorylation, Chemiosmosis, Mitochondrial Uncoupling. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Electron Transport Chain?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Electron Transport Chain. To practise the whole of Metabolism & Bioenergetics, use the Metabolism & Bioenergetics quiz.
How is Electron Transport Chain different from Light Reactions and ATP Synthesis?
Electron Transport Chain: Protein complexes in the inner mitochondrial membrane pass electrons to oxygen while pumping protons. Light Reactions and ATP Synthesis: Photosynthetic electron flow builds a proton gradient across the thylakoid to drive photophosphorylation. Read both side by side and note what each one explains.
How should I study Electron Transport Chain step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Light Reactions and ATP Synthesis and explain the difference aloud. Finally, take the Metabolism & Bioenergetics quiz and come back to this page for any question you miss.