Difference Between Glucose and Galactose

The key difference between glucose and galactose is the position of the –OH at the 4th carbon atom; the –OH group of the 4th carbon of glucose is directed towards the right side while the –OH group of the 4th carbon of galactose is directed towards the left side.

Glucose and galactose are categorized as carbohydrates. Carbohydrates are the most abundant type of organic molecules on earth. They are the source of chemical energy for living organisms. Not only this, they serve as important constituents of tissues. Carbohydrate can be categorized into three as monosaccharide, disaccharides and polysaccharides. Monosaccharides are the simplest carbohydrate type. Glucose and galactose are monosaccharides. Monosaccharides are classified according to the number of carbon atoms present in the molecule and whether they contain an aldehyde or keto group. Therefore, a monosaccharide with six carbon atoms is called a hexose. If there are five carbon atoms, then it is a pentose. Furthermore, if the monosaccharide has an aldehyde group, it is called aldose. A monosaccharide with a keto group is called a ketose.

1. Overview and Key Difference
2. What is Glucose
3. What is Galactose
4. Side by Side Comparison – Glucose vs Galactose in Tabular Form
5. Summary

What is Glucose?

Glucose is a monosaccharide that contains six carbon atoms and an aldehyde group. Therefore, it is a hexose and an aldose. It has four hydroxyl groups and has the following structure. Difference Between Glucose and Galactose

Though it is shown as a linear structure, glucose can be present as a cyclic structure too. In fact, in a solution, the majority of molecules are in the cyclic structure. When a cyclic structure is formed, the -OH on carbon 5 is converted into the ether linkage to close the ring with carbon 1. This forms a six-member ring structure. The ring is also called a hemiacetal ring, due to the presence of carbon that has both an ether oxygen and an alcohol group. Because of the free aldehyde group, glucose can be reduced. Thus, it is called a reducing sugar. Further, glucose is also known as dextrose because it rotates plane-polarized light to the right.

When there is sunlight, in plant chloroplasts, glucose is synthesized using water and carbon dioxide. This glucose is stored and used as a source of energy. Animals and human obtain glucose from plant sources. The glucose level in human blood is regulated by the homeostasis mechanism. Insulin and glucagon hormones are involved in the mechanism. When there is high glucose level in the blood, it is called a diabetic condition. The measurement of blood sugar level measures the glucose level in blood. There are various means to measure the blood glucose level.

What is Galactose?

Galactose is a hexose monosaccharide. It has an aldehyde group at the end of the molecule like glucose. It differs from glucose because of the way the –OH is located in the fourth carbon. Therefore, galactose is a C-4 epimer of glucose. Key Difference - Glucose vs Galactose

Galactose exists in both open-chain and cyclic form. Dairy food and sugar beet contain galactose. Galactose is also synthesized in our body. Galactose forms the disaccharide lactose, which is found in milk.

What is the Difference Between Glucose and Galactose?

The key difference between glucose and galactose is the position of the –OH at the 4th carbon atom; the –OH group of the 4th carbon of glucose is directed towards the right side while the –OH group of the 4th carbon of galactose is directed towards the left side. Moreover, glucose is more stable than galactose. Glucose also has a sweeter taste than galactose. In addition, galactose has a higher melting point than glucose. Difference Between Glucose and Galactose - Tabular Form

Summary – Glucose vs Galactose

The key difference between glucose and galactose is the position of the –OH at the 4th carbon atom; the –OH group of the 4th carbon of glucose is directed towards the right side while the –OH group of the 4th carbon of galactose is directed towards the left side. This difference in structure has led to several other differences between them.

Image Courtesy:

1. “D-glucose-chain-2D-Fischer” By Ben; Yikrazuul – Own work (Public Domain) via Commons Wikimedia
2. “GlucoseGalactose” By Lord Biro – Glucosetatuetata.jpg (Public Domain) via Commons Wikimedia