Carbohydrates

Structure and Function

• How do we define a carbohydrate?• aldehydes or ketones with multiple hydroxyl groups

• “hydrate” of carbon – C-H2O

• What are some of the functions of carbohydrates?• fuel for cells

• storage of energy

• cell structure

• metabolic intermediates

• cell-cell recognition

Monosaccharides

• How is an aldose different from a ketose?• H-C=O versus C=O

• How do we classify monosaccharides?• number of carbon atoms (3-9)

• trioses

• tetroses

• pentoses

• hexoses

Monosaccharides• What are enantiomers?

• D and L forms – D and L designate configuration of asymmetric carbon farthest from aldehyde or ketone group

Aldoses

Ketoses

Cyclization of Monosaccharides

• Aldehydes react with alcohols to form hemiacetals

• Aldohexoses such as glucose can form intramolecular hemiacetals.

Cyclization of Monosaccharides

Cyclization of Monosaccharides

• Ketones react with alcohols to form hemiketals.

• Ketohexoses such as fructose can form intramolecular hemiketals.

Cyclization of Monosaccharides

Cyclization of Monosaccharides

• Cyclization creates a second asymmetric carbon atom-D-glucopyranose and -D-glucopyranose

• depends upon position of group at carbon 1• C – 1 is anomeric carbon means hydroxyl group is below plane of ring means hydroxyl group is above plane of ring

-D-fructofuranose and -D-fructofuranose• C – 2 is anomeric carbon

Cyclization of Monosaccharides

• Fructose can form both 5-membered furanose and 6-membered pyranose rings

Monosaccharides

• To what do the terms chair ,boat , and envelope refer?

Monosaccharides

• What are glycosidic bonds?• formed from reaction of monosaccharide with alcohol

or with amine

Monosaccharides

• What are reducing sugars?• sugars that have free aldehyde group that are easily

oxidized by oxidizing agents such as Cu+2

Disaccharides

• How are disaccharides formed?

Disaccharides

• What are the most common disaccharides?• sucrose

• maltose

• lactose

Disaccharides

Disaccharides

Disaccharides

Polysaccharides

• What do glycogen and starch have in common?• polymers of glucose

• homopolymers

• How are glycogen and starch different?• glycogen - major storage form in animals

• starch – major storage form in plants

Polysaccharides

Polysaccharides

• What is the difference between amylose and amylopectin?• amylose is unbranched and amylopectin has branches

Polysaccharides

• How is cellulose similar to and different from starch?• both found in plants

• both made of glucose units

• cellulose is structural, starch is nutritional

• starch contains linkages and cellulose linkages

Polysaccharides

Polysaccharides

• What are glycosaminoglycans?• polysaccharides made of repeating units of

disaccharides containing a derivative of an amino sugar

• one of the sugars in unit has negatively charged carboxylate or sulfate group

• usually attached to proteins• proteoglycans

Glycosaminoglycans

Oligosaccharide Formation

• What are glycosyltransferases?• enzymes that catalyze

formation of glycosidic bonds

Glycosyltransferases

• What is the connection between these enzymes and the human blood groups?• A, B, and O blood groups have different

oligosaccharides attached to glycoproteins and glycolipids on surface

• A and B have one extra monosaccharide unit added by glycosyltransferase

Glycosyltransferases