Difference Between Glycogenolysis and Gluconeogenesis

Main Difference – Glycogenolysis vs Gluconeogenesis

Glycogenolysis and gluconeogenesis are two processes which are involved in the formation of glucose in the animal body. The carbohydrates in the diet are broken down into glucose and other monosaccharides during digestion. The glucose is transported into the liver and muscle cells by blood. That glucose is converted into a storage carbohydrate known as glycogen in a process called glycogenesis. The main difference between glycogenolysis and gluconeogenesis is that glycogenolysis is the production of glucose 6-phosphate by splitting a glucose monomer from glycogen by adding an inorganic phosphate whereas gluconeogenesis is the metabolic process by which glucose is formed from non-carbohydrate precursors in the liver.

Key Areas Covered

1. What is Glycogenolysis
      – Definition, Process, Reaction Pathway
2. What is Gluconeogenesis
      – Definition, Process, Reaction Pathway
3. What are the similarities between Glycogenolysis and Gluconeogenesis
      – Outline of Common Features
4. What is the difference between Glycogenolysis and Gluconeogenesis
      – Comparison of Key Differences

Key Terms: Adrenaline, Glucagon, Gluconeogenesis, Glucose, Glycerol, Glycogen, Glycogen Phosphorylase, Glycolysis, Glycogenolysis, Hexokinase, Phosphoglucomutase

What is Glycogenolysis

Glycogenolysis is a process by which stored glycogen is broken down into glucose monomers in the liver under the influence of hormones. Glucagon and adrenaline govern the breakdown of glycogen in the liver when less glucose is available for the metabolism in the cells. Glucagon is released in response to low glucose levels. Adrenaline is released in response to a threat or stress. The enzyme, glycogen phosphorylase produces glucose 1-phosphate by the phosphorylation of alpha(1,4) linkages. The second enzyme, phosphoglucomutase converts glucose 1-phosphate into glucose 6-phosphate. The alpha(1,6) linkages are responsible for the branching of glycogen. The action of glycogen debranching enzyme and alpha(1,6) glucosidase enzymes are involved in the removal of the glucose molecules, which form branches in the glycogen. The conversion of glucose 1-phosphate into glucose 6-phosphate is done by hexokinase. The phosphate group is removed by glucose 6-phosphatase during circulation and free glucose is readily available for the cells to be up taken. The bonds in the glycogen structure are shown in figure 1.

Figure 1: Glycogen

What is Gluconeogenesis

Gluconeogenesis is a process by which glucose is produced in the liver; this process starts from non-carbohydrate sources like amino acid or lactic acid. A small amount of gluconeogenesis occurs in the cortex of the kidney. Other than that, other tissues with high demand for glucose such as the brain, heart muscles, and skeletal muscles also serve as the sites of gluconeogenesis. The amino acid is provided by the breaking down of proteins in muscle cells by gluconeogenesis. The hydrolysis of lipids provides fatty acids and glycerol, and this glycerol is used in gluconeogenesis to produce glucose. Though gluconeogenesis is the exact reverse of glycolysis, it forms a glucose molecule by the joining of two pyruvate molecules. The initiation of gluconeogenesis occurs during carbohydrate starvation where less glucose is available for metabolism. The synthesized glucose is transported into the cells where metabolism occurs through the blood. The reaction pathway of gluconeogenesis is shown in figure 2.

Figure 2: Gluconeogenesis

Similarities Between Glycogenolysis and Gluconeogenesis

• Both glycogenolysis and gluconeogenesis are involved in the formation of glucose in the body.

• Both processes mainly occur in the liver and release glucose into the blood.

Difference Between Glycogenolysis and Gluconeogenesis

Definition

Glycogenolysis: Glycogenolysis is the production of glucose 6-phosphate by splitting a glucose monomer from glycogen by adding an inorganic phosphate.

Gluconeogenesis: Gluconeogenesis is the metabolic process by which glucose is formed from non-carbohydrate precursors in the liver.

Significance

Glycogenolysis: Glycogen is broken down in the liver during glycogenolysis.

Gluconeogenesis: Amino acid and lactic acid are used in the production of glucose in gluconeogenesis.

Type of Metabolism

Glycogenolysis: Glycogenolysis is a catabolic process.

Gluconeogenesis: Gluconeogenesis is an anabolic process.

Usage of ATP

Glycogenolysis: Less amount of ATP is consumed by glycogenolysis.

Gluconeogenesis: Six ATPs are used in the production of one glucose molecule by gluconeogenesis.

Occurrence

Glycogenolysis: Glycogenolysis occurs in the liver.

Gluconeogenesis: Gluconeogenesis occurs in the liver as well as the tissues with high glucose demand (ex: heart muscles, skeletal muscles, brain, and the cortex of the kidney).

Conclusion

Glycogenolysis and gluconeogenesis are two processes involved in the formation of glucose inside the body in response to low glucose levels. Both processes mainly occur in the liver. During glycogenolysis, glycogen is broken down into its monomer glucose. Glucose is produced by gluconeogenesis using amino acids and glycerol, which are obtained by the degradation of proteins and lipids in the body. Hence, the main difference of glycogenolysis and gluconeogenesis is the mechanisms by which each process produces glucose. 

Reference:

1. Ward, Colin. “Glycogenolysis and glycogenesis.” Metabolism, insulin and other hormones – Diapedia, The Living Textbook of Diabetes. N.p., n.d. Web. Available here. 24 June 2017.
2. “Glycogenesis, Glycogenolysis, and Gluconeogenesis.” Glycogenesis. N.p., n.d. Web. Available here. 24 June 2017. 
3. “Glycogenesis, Glycogenolysis, and Gluconeogenesis.” Study.com. N.p., n.d. Web. Available here. 24 June 2017. 

Image Courtesy:

1. “Glycogen” Public Domain) via Commons Wikimedia
2. “Gluconeogenesis pathway” By Unused0026 at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia

ncG1vNJzZmiolZm2oq2NnKamZ5Ses6ex0Z6lnJ1dl7K1w8SepWafnK6wsLPEp6alsaOewG6tzZ1koKSlmLyvsc6gnKedo57AcA%3D%3D