Question

Flow of electrons in $ETS$ is $NADH+H^{+}\left(NADPH+H^{+}\right)\to FMN\to FeS$ protein $\to CoQ\to$ $cytb\to cyt{c}_1\to cytc\to cyta\to cyt{a}_3\to o^{{}^{\prime \prime }}.$ At three steps $ATP$ is formed (oxidative phosphorylation). Where does II $ATP$ is generated?

• A. Between $NAD{H}_2$ and $FMN$
• B. $Cytb$ and $Cyt{c}_1$
• C. $Cyta$ and $Cyt{a}_3$
• D. $FMN\to FeS$ protein

Answer 1

Answer: (B)

The process of forming ATP through the electron transport chain is known as oxidative phosphorylation.
Electrons carried by NADH + H⁺ and FADH₂ are transferred to oxygen via a series of electron carriers, and ATPs are formed. Three ATPs are formed from each NADH + H⁺, and two ATPs are formed for each FADH₂. There are four complexes that are part of the electron transport chain that functions to pass electrons down the chain. A fifth protein complex serves to transport hydrogen ions back into the matrix.
NADH transfers two electrons to Complex-I resulting in four H⁺ ions being pumped across the inner membrane. NADH is oxidized to NAD⁺, which is recycled back into the cycle. Electrons are transferred from Complex-I to a carrier molecule ubiquinone (Q), which is reduced to ubiquinol (QH2). Ubiquinol carries the electrons to Complex-III. FADH₂ transfers electrons to Complex-II and the electrons are passed along to ubiquinone (Q). Q is reduced to ubiquinol (QH2), which carries the electrons to Complex-III. No H⁺ ions are transported to the intermembrane space in this process. The passage of electrons to Complex-III drives the transport of four more H⁺ ions across the inner membrane. QH2 is oxidized and electrons are passed to another electron carrier protein cytochrome C and ATP is generated during the flow of electrons and protons from Cyt b to Cyt c1.