Carbohydrates
Jan 16, 2016
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