What is the Difference Between Mannose and Glucose

The main difference between mannose and glucose is that mannose is important in glycoprotein biosynthesis whereas glucose is the most important source of energy in living organisms.

Mannose and glucose are two monosaccharide sugars important in metabolism. Both glucose and mannose circulate in the bloodstream.

Key Areas Covered

1. What is Mannose
   • Definition, Characteristics, Importance
2. What is Glucose
   • Definition, Characteristics, Importance
3. Similarities Between Mannose and Glucose
   • Outline of Common Features
4. Difference Between Mannose and Glucose
   • Comparison of Key Differences

Key Terms

Glucose, Mannose

What is Mannose

Mannose is a sugar monomer, an aldohexose. It is also a C-2 epimer of glucose. More importantly, the main function of the mannose is to help in the glycosylation of proteins. Generally, the mannose from the glycoprotein biosynthesis comes from extracellular mannose. The dietary mannose circulates throughout the body through the bloodstream. Significantly, glycoprotein biosynthesis occurs in the liver. Mannose is present in numerous glycoconjugates including N-linked glycosylation of proteins.

Figure 1: Mannose

Furthermore, the digestion of polysaccharides and glycoproteins yields mannose. Generally, hexokinase is the enzyme that phosphorylates mannose into mannose-6-phosphate. In addition, mannose-6-phosphate converts into fructose-6-phosphate by the enzyme phosphomannose isomerase and this enters into the glycolytic pathway, again converting into the glucose-6-phosphate. However, mannose is not an essential monosaccharide nutrient as it can be produced in the body from glucose.       

What is Glucose

Glucose is the simplest and the most common form of monosaccharide in both plants and animals. All living organisms use glucose as the main energy source of their cellular respiration. However, plants undergo photosynthesis to produce glucose. They store excess glucose in the form of starch and amylopectin. Plants produce one of the major structural polysaccharides, cellulose, by using glucose as the monomer. But, heterotrophs, such as animals use the glucose produced by plants. In addition, animals store glucose as glycogen. Usually, glucose circulates throughout the body in the form of blood sugar.

Figure 2: Glucose

Moreover, glucose in nature occurs in two forms of stereoisomers: D-glucose and L-glucose, which are enantiomers of each other. D-glucose or dextrose is the major form in nature, while L-glucose occurs desultory. Glucose occurs in two forms of structural isomers: open-chain form and cyclic form. The latter is the result of an intramolecular reaction between the aldehyde C atom and C-5 hydroxyl group to form an intramolecular hemiacetal. Generally, in a solution, the cyclic form is the predominant structure of glucose.

Similarities Between Mannose and Glucose

• Mannose and glucose are two types of monosaccharides and they are hexose sugars.
• They abundantly occur in the bloodstream.

Difference Between Mannose and Glucose

Definition

Mannose refers to a sugar of the hexose class that occurs as a component of many natural polysaccharides, while glucose refers to simple sugar, which is an important energy source in living organisms and is a component of many carbohydrates.

Structure

Mannose is a C-2 epimer of glucose while glucose is a hexose sugar.

Abundancy

Furthermore, mannose is abundant in the bloodstream while glucose is the most abundant monosaccharide.

In Metabolism

Mannose is important in glycoprotein metabolism while glucose is the main energy source of animals.

Production

Mannose is not an essential nutrient and it can be produced in the body from glucose while glucose is produced by plants in photosynthesis.

Conclusion

In brief, mannose and glucose are two monosaccharide sugars that occur in the bloodstream. Both are hexose sugars. Mannose is not an essential sugar and it can be produced from glucose, while glucose is produced by plants from photosynthesis. It is important in glycoprotein metabolism and glucose is the main energy source of animals. Moreover, glucose is the most abundant carbohydrate in animals. Therefore, the main difference between mannose and glucose is their function in metabolism.

References:

1. Wikimedia Foundation. (2022, July 25). Mannose. Wikipedia. Retrieved September 27, 2022.
2. Wikimedia Foundation. (2022, September 16). Glucose. Wikipedia. Retrieved September 27, 2022.

Image Courtesy:

1. “Mannose structure” By Ed (Edgar181) – Own work (Public Domain) via Commons Wikimedia
2. “Alpha-D-Glucopyranose” By NEUROtiker – Own Work (Public Domain) via Commons Wikimedia