Question

Oxidation of one \(\mathrm{NADH}_{2}\) and one \(\mathrm{FADH}_{2}\) respectively gives rise to *a) 3 and 2 (b) 2 and 1 \(\begin{array}{ll}2 \text { and } 3 & \text { (d) } 1 \text { and } 1\end{array}\)

Short answer

The oxidation of one NADH yields 3 ATP, and the oxidation of one FADH2 yields 2 ATP. Therefore, the correct answer is (a) 3 and 2.

Step-by-step solution

Understand the Electron Transport Chain

The electron transport chain is a series of compounds that transfer electrons from electron donors to electron acceptors via redox reactions, and couples this electron transfer with the transfer of protons (H+ ions) across a membrane. The process generates ATP, which the cell uses for energy. Typically, in eukaryotic cells, this process occurs in the mitochondria. NADH and FADH2 are electron donors in the electron transport chain, contributing to the ATP production.

Energy Yield from NADH Oxidation

The oxidation of one molecule of NADH in the electron transport chain generally leads to the production of three molecules of ATP. This is the theoretical yield under ideal conditions, but actual cellular conditions might lead to slightly less yield.

Energy Yield from FADH2 Oxidation

FADH2 enters the electron transport chain at a later point than NADH, which results in a slightly lower ATP yield. The oxidation of one molecule of FADH2 typically results in the production of two molecules of ATP.

Identifying the Correct Answer

Since the oxidation of one NADH molecule yields 3 ATP and the oxidation of one FADH2 molecule yields 2 ATP, the correct option is 'a) 3 and 2'.

Key concepts

ATP Production

The process of ATP production is fundamental to cellular energy supply, effectively fueling every action your cells undertake. ATP, or adenosine triphosphate, acts like a molecular currency in the biological economy; it is the primary energy carrier in all living organisms. It's created through a process called cellular respiration, which consists of several stages.

During the final stage of cellular respiration, known as the electron transport chain (ETC), energy stored in electron carriers NADH and FADH2 is converted into ATP. This is achieved by harvesting energy from electrons as they pass down the ETC, causing protons to be pumped across the mitochondrial membrane and thus creating a gradient. ATP synthase, an enzyme, takes advantage of this gradient to synthesize ATP in a mechanism analogous to a hydroelectric dam.

Why is ATP so important?

ATP is necessary for a myriad of cellular functions including active transport, muscle contraction, and biosynthesis of macromolecules. Without the constant production of ATP, cells would be unable to perform these vital activities.

Oxidation of NADH

NADH, or nicotinamide adenine dinucleotide (NAD) plus hydrogen (H), is a coenzyme that plays a vital role in the energy production of cells. Created during earlier stages of cellular respiration such as glycolysis and the Krebs cycle, NADH carries electrons to the electron transport chain where they can be utilized for ATP production.

Once in the ETC, NADH undergoes oxidation, meaning it loses electrons. This transference of electrons ultimately contributes to the pumping of protons across the mitochondrial membrane, facilitating the synthesis of ATP. Every molecule of oxidized NADH is typically assumed to yield three molecules of ATP, reflecting the efficiency of the ETC in harnessing the energy carried by these high-energy electrons.

What happens to the oxidized NADH?

After losing electrons, NADH is converted back into NAD+, ready to be used again in earlier stages of cellular respiration to pick up more electrons and thus continue the cycle of energy production.

Oxidation of FADH2

FADH2, or flavin adenine dinucleotide in its reduced form, is another coenzyme and electron carrier similar to NADH but with a different entry point and energy yield in the electron transport chain. FADH2 is also generated during the Krebs cycle but contributes its high-energy electrons further down the ETC compared to NADH.

As a result of this later entry, the electrons from FADH2 result in the translocation of fewer protons, correlating to the production of only two ATP molecules per oxidized FADH2. This lower yield is because FADH2 bypasses the first proton pump of the ETC, which is the site of greatest proton gradient production and thus a significant contributor to ATP synthesis.

Why does FADH2 yield less ATP?

It's simple: FADH2 contributes less to the proton gradient because its electrons enter the chain after the initial energy conversion stage. The diminished energy contribution means that fewer protons are pumped, leading to the generation of fewer ATP molecules.

Eukaryotic Cellular Respiration

Eukaryotic cellular respiration is a multi-step process that cells use to convert nutrients into energy. In eukaryotes, organisms with complex cellular structures, this process predominantly takes place within the mitochondria, known as the powerhouses of the cell.

Cellular respiration includes glycolysis, the Krebs cycle, and the electron transport chain, culminating in oxidative phosphorylation. Through these sequential processes, cells are able to harvest energy from the breakdown of glucose and other substrates, and convert it into ATP. The process not only produces ATP but also releases by-products like water and carbon dioxide. It's a beautiful and complex dance of chemistry and physics that ensures eukaryotic cells have the energy required for survival and function.

What makes eukaryotic respiration effective?

The organization of eukaryotic cells allows for efficient respiration. Mitochondria provide an ideal environment for the processes because of their inner membrane's extensive surface area, which is pivotal for the electron transport chain and ATP production. This specialization is a key reason eukaryotic cells can sustain more complex life forms.