What is the Difference Between Glucose and Fructose Metabolism

The main difference between glucose and fructose metabolism is that glucose can readily enter glycolysis whereas fructose first converts into the by-products of the glycolysis, which then undergo cellular respiration by entering through the Krebs cycle. Furthermore, glucose metabolism occurs in the cells throughout the body while the conversion of fructose into glucose by-products occurs in the liver.

Glucose and fructose metabolism are two types of metabolic pathways in the production of energy in the body. Here, both glucose and fructose are two monosaccharides.

Key Areas Covered

1. What is Glucose Metabolism
     – Definition, Anabolism, Catabolism
2. What is Fructose Metabolism
     – Definition, Anabolism, Catabolism
3. What are the Similarities Between Glucose and Fructose Metabolism
     – Outline of Common Features
4. What is the Difference Between Glucose and Fructose Metabolism
     – Comparison of Key Differences

Key Terms

Cellular Respiration, Fructose Metabolism, Glucose Metabolism, Glycogen, Glycolysis, Triglycerides

What is Glucose Metabolism

Glucose metabolism is the main process of the production of energy inside the cell. First, digestive enzymes break down carbohydrates in the food into glucose. And, this glucose enters the bloodstream through the walls of the intestine. Then, this glucose travels to the liver for metabolism in animals. The liver contains enzymes for the conversion of glucose into glycogen. The formation of storage forms of glucose occurs during the anabolism of glucose. In plants and fungi, the storage form of glucose is starch.

Figure 1: Cellular Respiration

Cellular respiration is the catabolic process of glucose metabolism. The three main steps of cellular respiration are glycolysis, Krebs cycle, and oxidative phosphorylation. Glycolysis occurs in the same way in almost all the cells. In eukaryotes, cellular respiration proceeds through the Krebs cycle and oxidative phosphorylation, which use molecular oxygen as the terminal electron acceptor. Therefore, this process is called aerobic respiration, which produces approximately 36 ATPs per glucose molecule. Significantly, fungi and bacteria undergo fermentation; here, products of glycolysis enter into incomplete oxidation in the absence of oxygen. Some bacteria undergo anaerobic respiration, which uses other inorganic compounds as the final electron acceptor. However, both fermentation and anaerobic respiration do not produce a high ATP yield as aerobic respiration.

What is Fructose Metabolism

Fructose metabolism is a subordinate process responsible for energy production. Fructose is a dietary monosaccharide naturally occurring mainly in fruits. In addition, sucrose is a disaccharide made up of glucose and fructose. Moreover, high fructose corn syrups are a major source of fructose in Western diets. In Western diets, around 10% of the calories come from fructose.

Figure 2: Conversion of Fructose into Trioses

The intestine absorbs fructose in the food and it travels to the liver through the bloodstream. The liver converts approximately 29-54% of fructose into the by-products of glycolysis, which can undergo regular metabolism, the same as the dietary glucose by converting into pyruvate. Approximately, 25% of the fructose converts into lactate. Lactate is also used in cellular metabolism. Around 15-18% of the fructose converts into glycogen, and around 1% of the fructose is used in the triglyceride synthesis.

Similarities Between Glucose and Fructose Metabolism

• Glucose and fructose metabolism are two types of metabolic processes which generate energy for the functioning of cells.
• Both glucose and fructose are two monosaccharides used in glycolysis.
• However, their metabolic pathways are independent of each other.
• Also, both sugars end up in the liver. 
• Besides, both types of metabolisms produce the same number of ATPs per molecule.

Difference Between Glucose and Fructose Metabolism

Definition

Glucose metabolism refers to the process by which simple sugars found in many foods are processed and used to produce energy in the form of ATP. In contrast, fructose metabolism refers to the metabolism of fructose from dietary sources. Therefore, this is the main difference between glucose and fructose metabolism.

Usage in Glycolysis

The main difference between glucose and fructose metabolismis that the glucose readily enters glycolysis while the fructose first converts into molecules that then enter the cellular respiration process.

Location of Metabolism

Location of metabolism is another difference between glucose and fructose metabolism. Glucose metabolism occurs inside the cells throughout the body while the conversion of fructose into glucose by-products occurs in the liver.

Effect of Insulin

Moreover, insulin regulates the metabolism of glucose while insulin has no effect on fructose metabolism.

Efficiency

Glucose metabolism releases energy fast while fructose metabolism releases energy slower. Hence, this is another difference between glucose and fructose metabolism.

Effect on Diabetes

Furthermore, glucose is not a good choice for diabetes while fructose is a good source for diabetes.

Anabolism

Besides, the anabolism of glucose produces glycogen while the anabolism of fructose produces both glycogen and triglycerides.

Conclusion

Glucose is the main molecule responsible for the production of energy inside cells. It is stored in the form of glycogen in animals. If not, it enters cellular respiration. On the other hand, fructose is another monosaccharide used in the cellular respiration after converting into glucose by-products in glycolysis. It also plays an important role in the synthesis of glycogen and triglycerides. Therefore, the main difference between glucose and fructose metabolism is the way they enter glycolysis.

Reference:

1. Glucose Metabolism – Function of Insulin and Glucagon. Caninsulin, Available Here
2. Sun, Sam Z and Mark W Empie. “Fructose metabolism in humans – what isotopic tracer studies tell us” Nutrition & metabolism vol. 9,1 89. 2 Oct. 2012, doi:10.1186/1743-7075-9-89. Available Here

Image Courtesy:

1. “Aerobic respiration summary” By ScienceGal4.0 – Own work (CC BY-SA 4.0) via Commons Wikimedia  
2. “Fructose to trioses” By Clariebh at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia