Carbohydrates Flashcards
Carbohydrate modification
Adding sugar molecules to other molecules
Enantiomers
Isomers that are mirror images of each other
Primary enantiomeric form of monosaccharides in nature
D form
Diastereoisomers
Isomers that are not mirror images of each other
Can be epimers or anomers
Epimers
Isomers that differ around only 1 chiral center
Isomers
Have same molecular formula but different structures
Can be constitutional isomers or stereoisomers
Constitutional isomers
Differ in the order of attachment of atoms
Stereoisomers
Atoms are connected in the same order but differ in spatial arrangement
Can be enantiomers or diastereoisomers
Anomers
Isomers that differ at a new asymmetric carbon atom formed on ring closure
Form of which most monosaccharides of chains 5 carbons or longer exist
Rings
Alpha vs. beta form of anomers
Alpha- hydroxyl at C1 or C2 is below ring
Beta- hydroxyl at C1 or C2 is above ring
Interchangeability of anomers
Anomers can interchange between their two forms without needing an enzyme to catalyze the reaction
Reducing sugars
Sugars without O- or N- linkages
Can be readily oxidized
Fehling’s solution
Test for reducing sugars: reducing sugars can reduce Cu+2 to Cu+
Consequences of phosphorylating sugars
- Make sugar more reactive
2. Glycolysis: trap glucose in cell (prevents diffusion and transport by transporters)
Glycosidic linkages
Linking two sugars together through an ether bond (1 carbon of one ring bonded to an oxygen bonded to a carbon of a different ring)
Reducing power of linked sugars
No reducing power- rings are linked together and won’t open up
Glycogen linkages
Heavily branched
Many alpha-1,4 and alpha-1,6 sugar linkages
Cellulose linkages
All beta-1,4 linkages
Oxygens in glycosidic bonds alternate between being above the rings and below the rings
Gives structural rigidity
Reason why cellulose can’t be digested
Enzymes don’t recognize beta-1,4 linkages
Proteoglycans
Proteins attracted to long repeats of glycosaminoglycans
Mostly sugar with a little protein
Function of proteoglycans
Exist at intersection of tissues: cushioning and shock absorption
Negative charges attract water
Function of glycosyltransferases
Enzymes that function in linking sugars during sorting in ER and Golgi
Active site of enzyme bind to Asn of protein (if N-linked) or Ser/Thr of protein (if O-linked) and also sugar
Get energy needed for reaction by ATP transferring phosphate
Function of UDP in reacting with sugar monomers
Charges monomer: gives it energy to move
Sugar linkages in blood type antigens
O antigen lacks sugar attached to Gal in chain
A and B antigens have different versions of sugar attached to Gal in chain
Glycoprotein
Proteins with sugar moieties
Mostly protein with a little sugar
Erythropoetin (EPO)
Example of glycoprotein
Triggers body to make RBCs when in low O2 environment
Synthetic version (sometimes used by athletes to cheat) has different glycosylation pattern, which can be detected by mass spec
Leukocyte rolling
Cells on surface of blood vessel express proteins with sugars attached to them in an attempt to attract WBCs
