4 - Glycolysis, Gluconeogenesis, Glycogenolysis, and Glycogenesis Comparisons

Why is controlling blood glucose levels important?

To ensure a continuous supply of glucose for tissues that depend on it exclusively (like the brain and red blood cells) and to prevent damage caused by excessively high or low glucose levels.

What is the role of glycolysis in blood glucose regulation?

Glycolysis reduces blood glucose levels by converting glucose to pyruvate for energy, especially in tissues like muscle and brain.

What is the role of gluconeogenesis in blood glucose regulation?

Gluconeogenesis increases blood glucose levels by synthesizing glucose from non-carbohydrate precursors, primarily in the liver and kidney.

What is the role of glycogenolysis in blood glucose regulation?

Glycogenolysis increases blood glucose by breaking down glycogen stores, especially in the liver, to release free glucose into the bloodstream.

What is the role of glycogenesis in blood glucose regulation?

Glycogenesis lowers blood glucose by storing excess glucose as glycogen in the liver and muscle.

Which tissues are absolutely dependent on glucose?

The brain and red blood cells (RBCs).

Why are red blood cells absolutely glucose dependent?

RBCs lack mitochondria and rely entirely on anaerobic glycolysis for ATP production.

Why is the brain absolutely dependent on glucose under normal conditions?

The brain uses glucose as its primary energy source and cannot use fatty acids directly due to the blood-brain barrier.

What are the key allosteric enzymes in glycolysis and gluconeogenesis?

• Glycolysis: Phosphofructokinase-1 (PFK-1), Pyruvate kinase

• Gluconeogenesis: Fructose-1,6-bisphosphatase, Pyruvate carboxylase

What are the key allosteric effectors of glycolysis?

• PFK-1 is activated by AMP, fructose-2,6-bisphosphate, and inhibited by ATP, citrate

• Pyruvate kinase is activated by fructose-1,6-bisphosphate, and inhibited by ATP, alanine

What are the key allosteric effectors of gluconeogenesis?

• Fructose-1,6-bisphosphatase is inhibited by AMP, fructose-2,6-bisphosphate

• Pyruvate carboxylase is activated by acetyl-CoA

What are the allosteric regulators in glycogen metabolism?

• Glycogen phosphorylase is activated by AMP (muscle), inhibited by ATP, glucose-6-phosphate

• Glycogen synthase is activated by glucose-6-phosphate

What is the effect of glucagon on liver glucose metabolism?

• Stimulates gluconeogenesis and glycogenolysis

• Inhibits glycolysis and glycogenesis

• Raises blood glucose

What is the effect of insulin on liver glucose metabolism?

• Stimulates glycolysis and glycogenesis

• Inhibits gluconeogenesis and glycogenolysis

• Lowers blood glucose

What is the effect of epinephrine on glucose metabolism in liver and muscle?

• Liver: Stimulates glycogenolysis, inhibits glycogenesis

• Muscle: Stimulates glycogenolysis and glycolysis to generate ATP

• Prepares tissues for energy demand

How does the liver regulate blood glucose through glycolysis and gluconeogenesis?

• Liver uses glycolysis when glucose is abundant

• Uses gluconeogenesis during fasting to release glucose into blood

How does the liver regulate blood glucose through glycogenesis and glycogenolysis?

• Stores glucose as glycogen (glycogenesis) after meals

• Breaks down glycogen (glycogenolysis) during fasting to release glucose

How does skeletal muscle regulate glucose through glycolysis and gluconeogenesis?

• Glycolysis is active during exercise for ATP

• Muscle does not perform gluconeogenesis

How does skeletal muscle regulate glucose through glycogenesis and glycogenolysis?

• Glycogenesis occurs after meals to store glucose

• Glycogenolysis is activated during exercise to provide glucose for glycolysis

• Glucose is not released to blood; used locally for energy