Carbohydrates Flashcards
The same sugars in different optical families, are enantiomers.
Two sugars that are in the same family (both are eithe rketoses or aldoses and have the same number of carbons) that are not identical and are not mirror images of each other are diastereomers.
A special subtype of diastereomers that differ in configuration at exactly on chiral center are epimers.
ketoses
- contain a ketone i.e. glucose
- can undergo intramolecular rxns to form hemiketals
aldoses
- contain an aldehyde i.e fructose
- can undergo intramolecular rxns to form cyclic hemiacetals
Alpha and Beta glucose
Monosaccharides
- monomer of carbohydrates
- contain alcohols and either aldehydes or ketones
- can undergo oxidation and reduction, esterification, and nucleophilic attack (creating glycosides)
Mutarotation
- spontaneous change of configuration about C1
- occurs more rapidly when rxn is catalyzed with an acid
Products: mixture of both alpha and beta anomers in equilibrium concentrations
Carbohydrate oxidation
- Oxidized aldoses are aldonic acids
- any monosaccharide with a hemiacetal ring is considered a reducing sugar
- When aldose in question is in ring form, oxidation yields a lactone instead.
- Tollen’s reagent and Benedict’s reagent are used to detect presence of reducing sugars
Tautomerization
- the rearrangement of bonds in a compound, usually by moving a hydrogen and forming a double bond.
- Ketones can tautomerize under basic conditions to form aldoses (give + Tollen’s/Benedict’s tests)
Esterification
- carbohydrates react with -COOHs to form esters
- similar to phosphorylation of glucose
Glycoside formation
- Hemiacetals + ROH + acid = acetals
- nonspecific; the anomeric carbon of a cyclic sugar can react with any hydroxyl group on any other sugar
Sucrose
glucose-a-1,2-fructose
Lactose
galactose-B-1,4-glucose
maltose
glucose-a-1,4-glucose
Cellulose
- main structural component of plants
- chain of B-D-glucose molecules
- Humans cannot digest
Starches
- More digestible by humans because they are linked a-D-glucose monomers
- amylose: linear with a-1,4 glycosidic bonds
- amylopectin: contains branches via a-1,6 glycosidic bonds
Glycogen
- carbohydrate storage in animals
- more a-1,6 glycosidic bonds (highly branched)
- makes it more soluble so more can be stored in body
Glycogen phosphorylase
cleaves glucose from the nonreducing end of a glycogen branch and phosphorylates it, thereby producing glucose 1-phosphate
