BCH210H1 Lecture Notes - Lecture 24: Anomer, Glycosyltransferase, Hydroxy Group

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BCH210 Lecture 22 Complex carbohydrates
Glycosidic bonds
- Monosaccharides are joined by O-glycosidic linkages to form disaccharides / sugar
polymers
- Intermolecular O-glycosidic bonds are formed between a hydroxyl group and a reactive
carbon on another molecule
- Water is lost in the condensation reaction
- Monosaccharide 1 sugar
- Disaccharide 2 sugars
- Oligosaccharide 3-20 sugars
- Polysaccharide 20+ sugars
- Glycoproteins may be:
o O-linked
Hydroxyl group on Ser/Thr
o N-linked
Amino group of Asp
- Glycoproteins are added in the ER and modified in the Golgi
o They help in protein folding
Naming disaccharides
1. Identify the atom in the linkage (O or N)
a. Oxygen joining two sugars or nitrogen
2. Configuration of the 1st sugar anomer + name -yl
a. Alpha or beta configuration
3. # of carbons that are linked together
a. Normally the anomeric carbon is on C-1
4. Configuration of the 2nd sugar anomer + name -ose -oside
Sugar sequencing
- Sugar sequencing is very difficult because there are:
o Different compositions
o Different connectivity
What hydroxyl or amino group (their position) attack the anomeric carbon
o Different configurations
Alpha and beta
Glycosyltransferase reactions
- Glycosyltransferases are enzymes that links sugars together
o They speed up glycosidic reactions by using an activated version of the sugar
- UDP-glucose is an activated, high-energy sugar nucleotide intermediate
- Allows glucose to be transferred onto another sugar / molecule
- Same reaction involved in order to add sugars to proteins to form glycoproteins
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