Write NADH and FADH, producing reactions of Krebs cycle. (IFS 2022, 10 Marks)

Introduction

NADH and FADH2 are electron carriers that play a crucial role in the Krebs cycle, also known as the citric acid cycle, which is a key metabolic pathway for generating ATP in aerobic respiration.

NADH and FADH2 Producing Reactions of the Krebs Cycle

The Krebs Cycle, also known as the Citric Acid Cycle or TCA (Tricarboxylic Acid) Cycle, is a critical part of cellular respiration occurring in the mitochondria. It involves a series of enzyme-driven reactions that generate energy-rich molecules to fuel cellular processes. NADH and FADH2, both electron carriers, are produced in this cycle and later utilized in the electron transport chain to generate ATP.

1. NADH-Producing Reactions: In the Krebs Cycle, three main steps result in the production of NADH. Each of these steps involves specific enzymatic reactions that convert intermediate molecules while reducing NAD+ to NADH.

• Isocitrate to Alpha-Ketoglutarate
  
  • Enzyme: Isocitrate Dehydrogenase.
  • Process: Isocitrate is oxidized to form alpha-ketoglutarate.
  • NADH Production: NAD+ is reduced to NADH in this reaction.
  • CO2_22 Release: One molecule of CO2_22 is released.
  • Significance: This reaction is a key regulatory step in the Krebs cycle.
• Alpha-Ketoglutarate to Succinyl-CoA
  
  • Enzyme: Alpha-Ketoglutarate Dehydrogenase.
  • Process: Alpha-ketoglutarate undergoes oxidative decarboxylation to form succinyl-CoA.
  • NADH Production: NAD+ is reduced to NADH.
  • CO2 Release: Another CO2 molecule is released in this reaction.
  • Significance: This step is tightly regulated and ensures efficient energy production.
• Malate to Oxaloacetate
  
  • Enzyme: Malate Dehydrogenase.
  • Process: Malate is oxidized to form oxaloacetate.
  • NADH Production: NAD+ is reduced to NADH.
  • Significance: The produced NADH will enter the electron transport chain, contributing to ATP synthesis.

2. FADH2 Producing Reaction: The Krebs Cycle includes one specific reaction where FADH2 is generated instead of NADH. FADH2 is another electron carrier that transfers electrons to the electron transport chain at a different complex, leading to slightly less ATP production compared to NADH.

• Succinate to Fumarate
  
  • Enzyme: Succinate Dehydrogenase.
  • Process: Succinate is oxidized to fumarate.
  • FADH2_22 Production: FAD is reduced to FADH2.
  • Location: Succinate dehydrogenase is unique as it is embedded in the mitochondrial membrane, linking the Krebs cycle to the electron transport chain directly.
  • Significance: FADH2 contributes electrons to the electron transport chain, producing ATP, albeit slightly less than NADH.

Conclusion

NADH and FADH2 producing reactions of the Krebs cycle are interconnected processes that work together to generate the energy needed for cellular functions. These pathways from a zoological perspective is important for comprehending the metabolic processes that sustain life in organisms.