Question

Which component of ETC transfers four protons?

• A. Complex I
• B. Complex II
• C. Complex III
• D. Complex IV

Answer 1

Answer: (A), (C)

The correct options are
A Complex I
C Complex III

An electron transport chain (ETC) is a series of complexes that transfer electrons from a donors to a acceptors via redox reactions.
Coupled to this electron transfer is the transfer of protons across a membrane, which creates an electrochemical gradient that drives the synthesis of ATP.
In mitochondria, electron transfer occurs through complexes I to IV on the inner membrane of the organelle.
Complex I is composed of flavin mononucleotide (FMN) and an enzyme containing iron-sulfur. It receives electrons from NADH2 and pump four protons across the membrane.
Complex II receives electrons only from FADH2 and passes it on to ubiquinone.This complex is not coupled to a proton pump.
The third complex called cytochrome oxidoreductase receives electrons from ubiquinone and passes it on to cytochrome C.
Complex IV receives the electron from cytochrome C and reduces oxygen to water.
Both Complex III and complex IV are coupled to proton pumps that help creates the electrochemical gradient necessary for ATP synthesis.
But only Complex I and Complex III pump four protons across the membrane.