Importance of Biochemistry

Galactose is a monosachride?

Galactose is a monosachride?

Galactose is a monosachride?

Galactose :

We can say that :

Galactose is a monosaccharide (ose) of the family of aldohexoses ; it has six atoms of carbon , so it is a hexose and there is a group aldehyde at one end, hence the term “aldohexose”.

 In the diet, galactose exists as D-galactose (D: dextrorotatory ). Galactose is one of two monosaccharides that make up lactose , a milk sugar .

 The hydrolysis of a molecule of lactose releases a galactose molecule and a glucose .

Glucose and galactose have the same chemical formula (C 6 H 12 O 6 ), they are epimers; they differ in their configuration in space: at the C4 carbon level, the OH group is not arranged in the same way.

Metabolism of galactose in the cell

In the cell, galactose can not be used directly by the enzymes of glycolysis to produce energy because they require glucose .

Galactose is therefore first phosphorylated to galactose-1-phosphate. Then it reacts with a molecule of UDP-glucose in the following reaction catalyzed by galactose-1-phosphate uridylyltransferase (GALT):

Galactose-1-phosphate + UDP-glucose -> glucose-1-phosphate (G1P) + UDP-galactose (UDP-Gal)

G1P is then converted to glucose-6-phosphate (G6P) through the intervention of the phosphoglucomutase enzyme .

G6P can then be used for energy-producing glycolysis for the cell. For its part, the UDP-Gal is recycled to UDP-glucose, by a reaction catalyzed by the enzyme UDP-galactose-4-epimerase, in the presence of NAD + . This UDP-glucose can again react with another molecule of galactose-1-phosphate.

The galactosemia is a genetic disease in which galactose can not be converted into glucose. This severe metabolic disease leads to mental retardation, severe liver damage , and even death in the neonatal period. It is often due to a deficiency of the enzyme GALT.

 Because of this enzymatic deficiency , galactose accumulates in the blood. A mild form of galactosemia promotes cataract . The treatment of galactosemia requires a diet without galactose.

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