Transcript CH_13_5_Disaccharides

Chapter 13 Carbohydrates
1
13.5
Disaccharides
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Important Disaccharides
2
A disaccharide consists of two monosaccharides.
Monosaccharides
Disaccharide
glucose + glucose
maltose + H2O
glucose + galactose
lactose + H2O
glucose + fructose
sucrose + H2O
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Maltose
3
Maltose is
• a disaccharide also known as malt sugar
• composed of two D-glucose molecules
• obtained from the hydrolysis of starch
• used in cereals, candies, and brewing
• found in both the  and β forms
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Formation of Maltose
4
Maltose is linked by an
-1,4-glycosidic bond
formed from the  OH on
carbon 1 of the first glucose
and OH on carbon 4 of the
second glucose.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Lactose
5
Lactose
• is found in milk and
milk products
• is a disaccharide of
β-D-galactose and
α- or β-D-glucose
• contains a
β-1,4-glycosidic bond
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Sucrose
6
Sucrose, or table sugar,
• is obtained from sugar cane
and sugar beets
• consists of α-D-glucose
and β-D-fructose
• has an α,β-1,2-glycosidic bond
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Sucrose
7
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
8
For the following disaccharide, list the two monosaccharide
units and the type of glycosidic bond present.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
9
For the following disaccharide, provide the reaction for two
monosaccharide units and the type of glycosidic bond present.
galactose + glucose
melibiose + H2O
The sugar melibiose is formed from two monosaccharides,
galactose and glucose, which are joined by a -1,6-glycosidic bond.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Sweetness of Sweeteners
10
Sugars and artificial
sweeteners
• differ in sweetness
• are compared to
sucrose (table sugar),
which is assigned a
value of 100
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Artificial Sweeteners - Sucralose
11
Sucrolose is made from
sucrose by replacing some
of the hydroxyl groups
with chlorine atoms.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Artificial Sweeteners - Aspartame
12
Aspartame is
• marketed as Nutra-Sweet
• a noncarbohydrate sweetener made from aspartic acid
and a methyl ester of the amino acid phenylalanine
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
13
Identify the monosaccharides in each of the following:
A. Lactose
(1) α-D-Glucose (2) β-D-Fructose
(3) β-D-Galactose
B. Maltose
(1) α-D-Glucose
(2) β-D-Fructose
(3) β-D-Galactose
C. Sucrose
(1) α-D-Glucose
(2) β-D-Fructose
(3) β-D-Galactose
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
14
Identify the monosaccharides in each of the following:
A. Lactose
(1) α-D-Glucose
(3) β-D-Galactose
B. Maltose
(1) α-D-Glucose
C. Sucrose
(1) α-D-Glucose
(2) β-D-Fructose
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.