In my textbook, I read the following description relating to the Electron Transport Chain (ETC):

The metabolic pathway through which electrons pass from one carrier to another is called the electron transport system (ETS).

(Note that “system” is used rather than “chain”)

But I thought that a metabolic pathway is a series of chemical reactions that a substrate undergoes to give a final product, whereas ETC is usually described in terms such as “protein complexes that transfer electrons via redox reactions and couples it with formation of proton gradient”.

Is the description in my textbook correct?

  • $\begingroup$ I have edited your question in two main respects. First the English in your quotation is poor suggesting that you have transcribed it incorrectly or that the text is of very low quality. When citing texts I you should give their name, date and place of publication. I have also replaced the word “defined” by “described” as this reflects better the nature of biochemical terminology. $\endgroup$
    – David
    Commented Apr 13 at 10:52

1 Answer 1


The original poster is correct in thinking that it is unusual to refer to the electron transport chain as a metabolic pathway.

This term is usually applied to metabolic processes in which there are a series of enzyme-catalysed reactions in each of which the product of one reaction is the starting reactant of the next. All the reactants are molecular in nature and an overall molecular conversion is achieved by a series of incremental conversions.

In contrast, in the electron transport chain one can identify only two molecular conversions overall: that of NADH + H+ to NAD+ (or FADH2 to FAD), and that of O2 to H2O. The other components of the electron transport chain merely links these reactions, with no overall change.

However, much of biochemical terminology is a matter of personal preference — there is no standards body “defining” terms like this. And it is somewhat ironic that although the editors of the Wikipedia entries provide a description of “metabolic pathway” that doesn’t accommodate the description of “electron transport chain”, the search autocomplete listing has as its expansion “energy-producing metabolic pathway”!

I suspect the prime consideration of the person responsible for this listing was brevity, but it does illustrate the different ways different people regard things. But I don’t share this attitude, myself.


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