Difference Between Glucose and Galactose

Glucose vs Galactose
 

Glucose and galactose are categorized as carbohydrates. Carbohydrates are a group of compounds which are defined as “polyhydroxy aldehydes and ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones.” 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 again 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
• 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. Further, if the monosaccharide has an aldehyde group, it is called as aldose. A monosaccharide with a keto group is called a ketose.

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.

Though it is shown as a linear structure, glucose can be present as a cyclic structure too. In fact in a solution, majority of the molecules are in the cyclic structure. When a cyclic structure is forming, 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 for energy. Animals and human obtain glucose from plant sources. Glucose level in human blood is regulated by homeostasis mechanism. Insulin and glucagon hormones are involved in the mechanism. When there is high glucose level in 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.

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. So galactose is a C-4 epimer of glucose.  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.

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