Question

Correct sequence of electron transport chain reactions is:

A. Substrate \(\rightarrow\) \(\text{NAD}^{+}\)

B. \(\text{NAD}^{+}\) \(\rightarrow\) FMN

C. \(\text{CoQ}\) \(\rightarrow\) \(\text{Cyt b}\)

D. \(\text{FMN}\) \(\rightarrow\) \(\text{CoQ}\)

E. \(\text{Cyt a}\) \(\rightarrow\) \(\text{Cyt a}_{3}\)

Choose the correct answer from the options given below:

• A. E, B, A, C, D \
• B. A, B, C, D, E \
• C. A, B, D, C, E \
• D. C, E, D, A, B

Hint:

Electrons move down a thermodynamic hill: Substrate $\rightarrow$ NADH $\rightarrow$ FMN $\rightarrow$ CoQ $\rightarrow$ Cytochromes (b $\rightarrow$ c $\rightarrow$ a $\rightarrow$ $\text{a}_{3}$) $\rightarrow$ $\text{O}_{2}$.

Answer 1

The Correct Option is C

Step 1: Concept The inner mitochondrial membrane houses the electron transport chain (ETC), where electrons move through a series of redox centers with increasing reduction potentials.

Step 2: Meaning Electrons flow from reduced electron carriers through specific complexes, ultimately reducing oxygen to water.

Step 3: Analysis Let us follow the natural path of electron flow through the chain: * First, a catabolic substrate reduces $\text{NAD}^{+}$ to $\text{NADH}$ (A). * $\text{NADH}$ passes its electrons to the flavin mononucleotide group of Complex I ($\text{NAD}^{+} \rightarrow \text{FMN}$) (B). * $\text{FMN}$ transfers those electrons down through iron-sulfur centers to Coenzyme Q ($\text{FMN} \rightarrow \text{CoQ}$) (D). * Mobile Coenzyme Q then delivers electrons to Cytochrome b within Complex III ($\text{CoQ} \rightarrow \text{Cyt b}$) (C). * Finally, within Complex IV, electrons travel from Cytochrome a to Cytochrome $\text{a}_{3}$ ($\text{Cyt a} \rightarrow \text{Cyt a}_{3}$) before reducing molecular oxygen (E).

Step 4: Conclusion The correct ordered sequence of these electron transfer events is A $\rightarrow$ B $\rightarrow$ D $\rightarrow$ C $\rightarrow$ E. This matches option C. Final Answer: (C)