CARBOHYDRATES
Di, poly-Carbohydrates Carbo MiniTopics
Review
 Elmhurst College
Classification Glucose Fructose  Chemistry Department
Carbo - Isomers Galactose Ribose  Virtual ChemBook

 Galactose

Galactose is more commonly found in the disaccharide, lactose or milk sugar. It is found as the monosaccharide in peas.

Galactose is classified as a monosaccharide, an aldose, a hexose, and is a reducing sugar.

Galactosemia - Genetic Enzyme Deficiency:

One baby out of every 18,000 is born with a genetic defect of not being able to utilize galactose. Since galactose is in milk as part of lactose, it will build up in the blood and urine. Undiagnosed it may lead to mental retardation, failure to grow, formation of cataracts, and in sever cases death by liver damage. The disorder is caused by a deficiency in one or more enzymes required to metabolize galactose.

The treatment for the disorder is to use a formula based upon the sugar sucrose rather than milk with lactose. The galactose free diet is critical only in infancy, since with maturation another enzyme is developed that can metabolize galactose.


Click for larger image 


Ring Structure for Galactose:

The chair form of galactose follows the same pattern as that for glucose.

Open graphic of glucose in a new window

Hemiacetal Functional Group:

The anomeric carbon is the center of a hemiacetal functional group. A carbon that has both an ether oxygen and an alcohol group is a hemiacetal.

Open graphic of hemiacetal in a new window

Which carbon in the structure on the left is the anomeric carbon?
Then check the answer from the drop down menu.

Compare Alpha and Beta Galactose in the Chair form (left graphic):

The Beta position is defined as the -OH being on the same side of the ring as the C # 6. In the chair structure this results in a horizontal projection,(Haworth - an upwards projection).

The Alpha position is defined as the -OH being on the opposite side of the ring as the C # 6. In the chair and Haworth structure this results in a downward projection.

Haworth Structures:

Open graphic of Haworth Structures in a new window

Compare Alpha and Beta Galactose - Chime in new window




Click for larger image 

 

Compare Glucose and Galactose in the Chair Structures:

The position of the -OH group on the carbon (#4) is the only distinction between glucose and galactose.

Glucose is defined as the -OH on C # 4 in a horizontal projection in the chair form, (down in the Haworth structure).

Galactose is defined as the -OH on C # 4 in a upward projection in the chair form,(also upward in the Haworth structure).

Both glucose and galactose may be either alpha or beta on the anomeric carbon, so this is not distinctive between them

Compare Glucose and Galactose - Chime in new window

Quiz on Glucose and Galactose:

Write down your answers.
Then check the answers from the drop down menu.

Which structure is shown in the graphic - glucose or galactose?
Is the structure alpha or beta ?  
 Open graphic of Chair Structures in a new window
 Open graphic of Haworth Structures in a new window

Which structure is shown in the graphic - glucose or galactose?
Is the structure alpha or beta ?  
 Open graphic of Chair Structures in a new window
 Open graphic of Haworth Structures in a new window