Question

Name the following pathways: (a) Pathway for synthesis of glycogen (b) Pathway for release of glucose from glycogen (c) Pathway for synthesis of glucose from lactate

Short answer

(a) Glycogenesis, (b) Glycogenolysis, (c) Gluconeogenesis.

Step-by-step solution

Determine the pathway for synthesis of glycogen

The synthesis of glycogen from glucose is known as glycogenesis. This process involves the conversion of glucose into glucose-1-phosphate and then into glycogen using an enzymatic process.

Identify the pathway for release of glucose from glycogen

The breakdown of glycogen to release glucose is called glycogenolysis. During this process, glycogen is broken down into glucose-1-phosphate and then converted into glucose-6-phosphate, which can enter the bloodstream as glucose.

Name the pathway for synthesis of glucose from lactate

The synthesis of glucose from lactate and other non-carbohydrate precursors is called gluconeogenesis. This pathway occurs primarily in the liver and involves converting lactate into glucose.

Key concepts

Glycogenesis

Glycogenesis is the process by which our bodies convert glucose into glycogen for storage. This is essential because glycogen serves as a readily available source of energy that the body can use during moments of intense physical activity or between meals.

• The process begins with glucose molecules.
• Glucose is first converted into glucose-1-phosphate by the action of the enzyme phosphoglucomutase.
• Next, a molecule called UDP-glucose is formed from glucose-1-phosphate and uridine triphosphate (UTP), catalyzed by the enzyme UDP-glucose pyrophosphorylase.
• The final step involves the enzyme glycogen synthase, which adds the UDP-glucose to a growing glycogen chain.

This is a highly regulated process, influenced by hormonal signals like insulin, which signals that the body has a sufficient energy supply and can store excess glucose as glycogen.

Glycogenolysis

Glycogenolysis is the metabolic pathway through which glycogen is broken down into glucose to provide an immediate supply of energy.

• In glycogenolysis, the enzyme glycogen phosphorylase breaks down glycogen by removing glucose units as glucose-1-phosphate.
• The glucose-1-phosphate is then converted into glucose-6-phosphate by the enzyme phosphoglucomutase.
• Finally, glucose-6-phosphate can be converted to glucose, particularly in the liver, allowing it to enter the bloodstream.

This pathway is mainly activated during fasting or intense physical activity when the body requires additional glucose.
It is regulated by hormones such as glucagon and adrenaline, which signal the need for increased glucose in the bloodstream.

Gluconeogenesis

Gluconeogenesis is the body's way of creating glucose from non-carbohydrate sources, such as lactate, amino acids, and glycerol. This pathway is especially vital during periods of fasting or strenuous exercise when glucose levels are low.

• Gluconeogenesis primarily takes place in the liver, though it also occurs in smaller amounts in the kidneys.
• The pathway involves several key enzymes, including pyruvate carboxylase and phosphoenolpyruvate carboxykinase (PEPCK), which help convert these non-carbohydrates back into intermediates that can function in the glycolytic pathway.
• Through a series of reactions set in reverse of glycolysis, lactate and other molecules are ultimately converted back into glucose.

Gluconeogenesis is crucial for maintaining blood glucose levels, particularly during times when carbohydrate intake is low, ensuring that organs and tissues, especially the brain, have a constant energy supply.