Sugars
• Polyhydroxy AND aldehyde or ketone
• Fischer projection:
– Linear structure, depicts stereochemistry
– D- or L- from stereochemistry of distal carbon
– Name from stereochem of other carbons
• Sugars typically cyclic in solution
– Usually last hydroxyl attacks carbonyl carbon
– Generates additional stereocenter
• Reversible attack: Mutarotation
– Cyclic form not flat: chair form
• Glycosidic bond
– Polymerization of sugars
– Through epimeric hydroxyl: hemiacetal → acetal
• Lose tendency for mutarotation
Polysaccharides
• Branching:
– Donor hydroxyl forming the acetal need not
be the 4 carbon
Polysaccharides
• Branching: two (or more) hydroxyls form
acetals with other monosaccharides
Polysaccharides
• Energy storage
– Store glucose as a polymer
• Starch: plant cells
• Glycogen: animal cells
– Can have lots of glucose with minimal
osmolarity
– No defined molecular weight, no ‘template’ (à
la DNA/protein synthesis)
• Characteristics a consequence of
chemistry/enzymology
Polysaccharides
• Energy sources:
– Compact storage, but end monosacch are
accessible to enzymatic removal (a1→4)
• Structural polysaccharides
– Cellulose (plants), chitin (bugs)
• Highly hydrogen bonded: compact, strong
 b1→4 linkages: mammalian cells lack the enzyme
to degrade
Cellulose
Chitin: b1→4 linkages
a1→4 linkages
Sugar/peptide conjugates
• Peptidoglycans
– eg. bacterial cell wall
Sugar/peptide conjugates
• Proteoglycans
– Multicellular organisms: usually extracellular
biomolecules
• connective tissue
• cellular adhesion molecules
• lots of hydrogen/non-covalent bonding
– Dominated by carbohydrate
• Mass
• Biological activity
– Sugar joined to the peptide through a hydroxyl on the
protein
Sugar/peptide conjugates
• Glycoproteins
– Proteins have the biological activity: modified or
protected by the carbohydrates
– Typically extracellular proteins (secreted) or
extracellular regions of integral membrane proteins
– Saccharides added in ER and Golgi
– Sugars protect the protein component from
extracellular proteases
– Sugars influence binding by other proteins/molecules
• Lectins (eg. P-selectin) recognize/bind specific sugars &
mediate cell-cell interactions