Question

Which reactions of the citric acid cycle transfer energy as \(\mathrm{FADH}_{2} ?\)

Short answer

The conversion of succinate to fumarate transfers energy as \(\mathrm{FADH}_{2}\) in the citric acid cycle.

Step-by-step solution

Identify the Reactions

The citric acid cycle, also known as the Krebs cycle, includes multiple steps. To identify reactions that transfer energy as \(\mathrm{FADH}_{2}\), we need to know which specific steps involve this molecule. Typically, one reaction in the citric acid cycle involves the formation of \(\mathrm{FADH}_{2}\).

Locate FADH2 Producing Reaction

In the citric acid cycle, the conversion of succinate to fumarate is catalyzed by the enzyme succinate dehydrogenase. During this reaction, FAD is reduced to \(\mathrm{FADH}_{2}\), producing energy.

Key concepts

FADH2

The molecule \(\mathrm{FADH}_{2}\) plays a significant role in cellular respiration, specifically within the citric acid cycle. It acts as an important electron carrier. In this context, \(\mathrm{FADH}_{2}\) stores and later transports electrons to the electron transport chain.
During the citric acid cycle, several reactions occur to generate energy. One crucial part of it involves the production of \(\mathrm{FADH}_{2}\) from FAD (flavin adenine dinucleotide). This process happens through redox reactions, where \(\mathrm{FAD}\) is reduced to \(\mathrm{FADH}_{2}\).

• \(\mathrm{FADH}_{2}\) is produced in the mitochondria alongside ATP and NADH, making it essential for energy conversion.
• It carries electrons to the electron transport chain, located in the inner membrane of the mitochondria.
• The energy release upon electron transport aids in additional ATP synthesis.

Understanding the role of \(\mathrm{FADH}_{2}\) is fundamental to comprehending how cells harvest energy efficiently from nutrient molecules.

Succinate to Fumarate

In the citric acid cycle, the transformation of succinate to fumarate is a key reaction. This conversion is vital for the overall cycle because it involves energy transfer through electron carriers like \(\mathrm{FADH}_{2}\).
Succinate is a four-carbon compound that undergoes dehydrogenation to become fumarate, another four-carbon compound. This specific step stands out as it directly links to the production of \(\mathrm{FADH}_{2}\), unlike other reactions in the cycle.

• Succinate loses hydrogen atoms during this process, which are picked up by FAD, reducing it to \(\mathrm{FADH}_{2}\).
• Even though it doesn't release carbon as carbon dioxide, its significance lies in electron capture and transfer.
• This reaction contributes to the relay of electrons to the electron transport chain, enabling further ATP production.

By understanding this conversion, students can appreciate how substrates are transformed and how their electrons are managed within the metabolic pathway.

Succinate Dehydrogenase

Succinate dehydrogenase is an enzyme that plays a pivotal role in both the citric acid cycle and the electron transport chain. It catalyzes the conversion of succinate to fumarate, and facilitates the reduction of FAD to \(\mathrm{FADH}_{2}\).
This unique enzyme is the only one in the cycle that is embedded in the inner mitochondrial membrane. It effectively bridges the gap between both metabolic pathways.

• It acts as a catalyst, speeding up the transformation of succinate to fumarate.
• Beyond the citric acid cycle, it participates in passing electrons from \(\mathrm{FADH}_{2}\) directly to the electron transport chain.
• Ensuring efficient function of succinate dehydrogenase is crucial for maintaining energy production in cells.

Understanding the role of succinate dehydrogenase helps elucidate how tightly cellular respiration processes are interconnected and how enzymes facilitate these complex reactions efficiently.