Gluconeogenesis

Summary

In this video, we explore the process of gluconeogenesis, which is the production of new glucose in the body. The presenter explains how glucose is vital for various organs and how the liver maintains glucose levels through glycogenolysis and gluconeogenesis. The video dives into key substrates like lactate, pyruvate, and gluconeogenic amino acids. It also covers the biochemical reactions that differentiate gluconeogenesis from glycolysis, detailing the enzymes that bypass irreversible steps in glycolysis. The video concludes with the importance of gluconeogenesis in maintaining blood glucose during fasting.

Takeaways

• 👋 The video introduces the topic of gluconeogenesis and explains the importance of glucose regulation in the body.
• 🧠 Organs like the brain, red blood cells, kidneys, and muscles need a continuous supply of glucose for proper functioning.
• 🍽 The primary source of glucose is exogenous, coming from the food we eat, especially carbohydrates.
• ⏳ Exogenous glucose is used up within 4 to 5 hours, and glycogen breakdown provides glucose during fasting for 10 to 18 hours.
• ⚙️ Gluconeogenesis becomes the sole source of glucose after prolonged fasting (24 to 48 hours).
• 🧬 Important substrates for gluconeogenesis include lactate, pyruvate, glycerol 3-phosphate, and gluconeogenic amino acids.
• 🧪 Alanine is the major gluconeogenic amino acid, while fatty acids can't generally be converted into glucose (except odd-number carbon fatty acids).
• 🔄 Gluconeogenesis overcomes three irreversible reactions from glycolysis using alternate enzymes: pyruvate carboxylase, PEP carboxykinase, and fructose-1,6-bisphosphatase.
• 🏭 Glucose-6-phosphatase replaces hexokinase in gluconeogenesis and is found only in the liver, not in muscles.
• 🔚 The video concludes by emphasizing that the liver produces glucose via gluconeogenesis but cannot use it for its own energy.

Q & A

What is the primary topic discussed in the video?

The video discusses gluconeogenesis, the process of producing new glucose in the body, particularly during fasting or prolonged periods without carbohydrate intake.

Why is glucose important for the body?

Glucose is essential for the functioning of several organs, including the brain, red blood cells, kidney medulla, lens, cornea, testes, and exercising muscles, which need a continuous supply to remain functional.

What role does the liver play in glucose regulation?

The liver maintains blood glucose levels by supplying glucose to organs, primarily through the processes of glycogenolysis (breaking down glycogen) and gluconeogenesis (producing new glucose).

What are the two main processes that maintain glucose levels during fasting?

During fasting, glucose levels are maintained through glycogenolysis, which lasts for 10-18 hours, and gluconeogenesis, which becomes the primary source of glucose after 24-48 hours.

Which organs produce glucose during an overnight fast and during prolonged fasting?

During an overnight fast, 90% of glucose is produced by the liver, and 10% by the kidneys. In prolonged fasting, the kidneys become the major source of glucose production.

What are the key substrates for gluconeogenesis?

The key substrates for gluconeogenesis are lactate (from anaerobic glycolysis), pyruvate (from aerobic glycolysis), glycerol 3-phosphate (from triglycerides), and gluconeogenic amino acids (except leucine and lysine).

Why can't humans convert fatty acids into glucose, and what is the exception?

Humans cannot convert most fatty acids into glucose because the pathway is not available, except for odd-chain fatty acids, which can produce small amounts of gluconeogenic Propionyl-CoA.

What are the three irreversible reactions in glycolysis that need to be bypassed in gluconeogenesis?

The three irreversible reactions in glycolysis that must be bypassed are steps 1 (hexokinase), 3 (phosphofructokinase-1), and 10 (pyruvate kinase).

How is the irreversible reaction 10 of glycolysis bypassed in gluconeogenesis?

Reaction 10 is bypassed by two enzymes: pyruvate carboxylase, which converts pyruvate to oxaloacetate, and PEP carboxykinase, which converts oxaloacetate to phosphoenolpyruvate (PEP).

What enzyme is responsible for the final conversion to free glucose in gluconeogenesis?

Glucose-6-phosphatase is responsible for converting glucose-6-phosphate into free glucose in the endoplasmic reticulum. This enzyme is specific to the liver and not present in skeletal muscles.