Maintenance of Redox Neutrality | Summary and Q&A

TL;DR

Cells use lactate dehydrogenase, glycerol-3-phosphate shuttle, and malate-aspartate shuttle to maintain redox neutrality in the cytoplasm.

Key Insights

• ❓ Maintaining redox neutrality is crucial for the continuous operation of glycolysis.
• 🎚️ The lactate dehydrogenase system, glycerol-3-phosphate shuttle, and malate-aspartate shuttle are three strategies used by cells to balance NAD+ and NADH levels.
• 🖐️ Lactate and aspartate serve as electron sinks, while quinone and the electron transport chain play critical roles in restoring NAD+.

Transcript

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Questions & Answers

Q: Why is it necessary to maintain redox neutrality in the cytoplasm of cells?

Redox neutrality is important to ensure that glycolysis, a crucial metabolic process, can continue without any interruptions. If the balance of NAD+ and NADH is disrupted, glycolysis cannot proceed efficiently.

Q: How does the lactate dehydrogenase system maintain redox neutrality?

The lactate dehydrogenase enzyme transfers electrons from NADH to lactate, which serves as an electron sink. The lactate can then be transported out of the cell and converted back to glucose through gluconeogenesis, thus replenishing the NAD+ pool.

Q: What is the role of the glycerol-3-phosphate shuttle in maintaining redox neutrality?

The glycerol-3-phosphate shuttle transfers electrons from NADH to quinone, a mobile electron carrier. The electrons are eventually transferred to oxygen through the electron transport chain, regenerating NAD+ and maintaining redox neutrality.

Q: How does the malate-aspartate shuttle contribute to redox neutrality?

The malate-aspartate shuttle uses malate and oxaloacetate to transfer electrons from NADH to NAD+ between the cytoplasm and mitochondria. Oxaloacetate is temporarily converted to aspartate in the mitochondria, which can be transported out and converted back to oxaloacetate in the cytoplasm, maintaining redox neutrality.

Summary & Key Takeaways

• Glycolysis consumes NAD+ and converts it to NADH, so cells need to find ways to convert NADH back to NAD+ for continuous glycolysis.

• The three strategies for maintaining redox neutrality in the cytoplasm are lactate dehydrogenase, glycerol-3-phosphate shuttle, and malate-aspartate shuttle.

• Lactate dehydrogenase transfers electrons from NADH to lactate, which is then transported out of the cell and can be converted back to glucose through gluconeogenesis.