Biochem Exam 3

Carbon hydrates, with a rough chemical composition of (C*H20)_n

• Sugar
• Optically active and chiral

Monomer unit of a sugar molecule

Small polymer of monosaccharides

Larger polymer of monosaccharide groups linked together

Oligosaccharides linked to protein

Oligosaccharides linked to lipids

Keytone as the carbonyl group

• Aldehyde as the carbonyl group
• 

D-sugars

• Molecules (sugars) are identical except rotation around one asymmetric carbon
• 

D-Glyceraldehyde

Aldotriose

D-Erythrose

Aldotetroses

D-Ribose

Aldopentoses

D-Xylose

Aldopentoses

D-Galactose

Aldohexoses

D-Mannose

Aldohexoses

D-Glucose

Aldohexoses

Dihydroxyacetone

Ketotriose

D-Erythrulose

Ketotetrose

D-Ribulose

Ketopentoses

D-Xylulose

Ketopentoses

D-Fructose

Ketohexoses

• Sugars with a 5-membered ring
• 

• Sugars with a 6-membered ring
• 

By nuc attack of the carbonyl by an alcohol to form either a hemiacetal or hemiketal

In this, the carbonyl becomes a new stereo center and is referred to as the anomeric carbon (C*)

• 
• OH is pointing down

• 
• OH is pointing up

Conversion between alpha and beta anomers

Simplified method of drawing ring structures with the plane of the ring perpendicular to the page (not geometrically precise)

Alpha-D-Glucofuranose

Beta-D-Glucofuranose

• Fructose forms furanose and pyranose 
• 
• 

• Aldehyde group may act as a reducing agent and may oxidized to carboxylic acid
• Sugar containing an aldehyde group is called this

Aldehyde oxidized to carboxylic acid

Primary alcohol oxidized to carboxylic acid

• Aldehyde and ketone groups can be reduced under mild conditions to yield this
• 

Popular sugar alcohol that is used as sweetener in chewing gum

• Any bonding of the sugar anomeric group (alpha or beta form) generates this
• After the anomeric alcohol reacts, the glycosidic bond is stable and the anomers can no longer interconvert by mutarotation

Enzymes which selectively cleave glycosidic bonds are required to break the formed bond