1. Disaccharides Chapter 17 Section 3

2. Disaccharides Consist of two monosaccharides joined through an “oxygen bridge” The carbon-oxygen bonds are called glycosidic bonds. Glycosidic bond formation is nonspecific. It can occur between a hemiketal or hemiacetal and any of the hydroxyl groups on the second monosaccharide.

3. Common Disaccharides β-Maltose O

4. Common Disaccharides β-Lactose

5. Common Disaccharides Sucrose O

6. Maltose AKA Malt sugar C-1 hydroxyl group of α-D-glucose is attached to C-4 of another glucose, the disaccharide is bonded by an α(1  4) glycosidic bond.

7. Lactose AKA milk sugar Disaccharide made up of one molecule of β-D-galactose and one of either α- or β-D- glucose. C-1 hydroxyl group of β-D-galactose is bonded to the C-4 hydroxyl group of either α- or β-D-glucose forming a β(1  4) glycosidic bond.

8. Importance of Lactose Lactose is the principal sugar in mammalian milk. In order to be used as an energy source, lactose must be hydrolyzed to produce glucose and galactose. A series of reactions are needed to convert galactose into a usable glucose form.

9. Galactosemia Genetic disease caused by the absence of one or more of the enzymes needed to convert galactose to usable glucose. This causes a toxic compound to form. If the condition is not treated, it can lead to severe mental retardation, cataracts, and early death. Treatment involves a diet without lactose (no milk or milk products)

10. Lactose Intolerance Many adults and children are unable to hydrolyze lactose because they are lacking the enzyme lactase. Undigested lactose causes cramping and diarrhea leading to dehydration. Effects can be avoided by eliminating milk and milk products or by supplementing the diet with lactase pills.

11. Sucrose AKA table sugar, cane sugar, or beet sugar Found only in plants; cannot be synthesized by animals Widely used as a sweetener Average American consumes 100-125 lbs of sucrose each year Empty calories – contains no vitamins or minerals

12. Sucrose Only negative scientifically proven association with sucrose is with the formation of cavities (Read pg. 470!) Disaccharide of α-D-glucose joined to β-D- fructose forming a α1  β2 glycosidic linkage As a result, the ring structure cannot open, so it will not react with Benedict’s reagent.

13. Homework Page 493: 17.37-42 These will be on the weekly quiz!!!!!!!