Chapter 16 Carbohydrates

1
Chapter 16Carbohydrates

• Sugars
• Saccharides
• Carbohydrates

2
(No Transcript)
3
Excess Sugar

• Glucose is absorbed after meals
• Excess glucose in blood (not absorbed) is
  secreted in urine
• Urine can be tested for the presence and
  concentration of glucose by Benedicts reagent
  or, more accurately, by glucose oxidase

4
Types of Carbohydrates

• Monosaccharide glucose (dextrose)
• Disaccharide sucrose
• Polysaccharide starch

5
Types of Carbohydrates

• 3-8 unbranched carbons 1 attached to carbonyl
  and the rest to hydroxyl groups
• Aldose Carbonyl aldehyde (-CHO)
• Ketose Carbonyl ketose (O)

Ketose
Aldose
6
The Implications of StereochemistryThe
Thalidomide Problem
7
Stereochemistry
Classification Chiral carbon FURTHEST from
carbonyl OH on left L-isomer OH on right
D-isomer
NOTE D is most common in nature
8
Open-chain vs. cyclic sugar Aldohexose
Anomeric carbon -OH UP beta (?) -OH DOWN
alpha (a)
9

• Contained in starch
• Pasta, potatoes
• Yummy!

• Contained in cellulose
• Wood, paper
• Not digestible

Humans have a-amylase but not ?-amylase
10
Mutarotation
Anomeric carbon a orientation
Anomeric carbon ? orientation
11
Aldopentose Ribose
As in RIBOnucleic Acid (RNA) and deoxyRIBOnucleic
Acid
12
Chemistry of CarbohydratesOxidation
Benedicts Reagent
Carbohydrates that can be oxidized are called
reducing sugars
13
?-D-Glucose
Methanol
Methyl-?-D-Glucoside
Glycosidic bond
Reducing sugar
Non-reducing sugar
14
Chemistry of CarbohydratesReduction
Sugar alcohol Used as artificial sweeteners May
cause cataracts
15
Disaccharides

• Maltose H2O (in acid) ? 2 glucose
• Lactose H2O (in acid) ? glucose galactose
• Sucrose H2O (in acid) ? glucose fructose

16
2 Glucose (a-D)
a-Maltose
a-Lactose
?-D-Galactose a-D-Glucose
D-Glucose
Sucrose
D-Fructose
17
Polysaccharides Plants
Amylose Straight chains of a-D-Glucose
a-1,4-glycosidic bonds Amylopectin Branched
chain of a-D-Glucose
18
PolysaccharidesCellulose

• Structural polymer
• Like amylopectin, an unbranched chain of glucose
• Unlike amlyopectin, glycosidic bond is
  ?-1,4-glucose
• Interactions between parallel chains form strong,
  fibrous material
• Plant cell walls, paper, wood

19
Polysaccharides Animals

• Glycogen Storage of glucose in liver and muscle.
  
• Like amylopectin more branching
• Hydrolyzed and condensed to maintain HOMEOSTASIS
  of blood glucose

Presence of starch can be tested with I2 Remember
lab experiment?