Carbohydrates Flashcards
Most abundant class of biological molecules
Carbohydrates
Monosaccharide
Smallest unit of carbohydrate structure Empirical formula (CH2O)n, where n= 3-9 (5-6 common)
Oligosaccharide
Polymers containing 2-20 monosaccharide residues
Polysaccharide
Polymers that typically contain more than 20 residues
2 types of monosaccharides
Aldoses (aldehydes)
Ketoses (ketones)
Epimers
Stereoisomers that differ in configuration at only 1 chiral center
Hemiacetal/hemiketal
Structure with hydroxyl group and ether at same carbon
2 forms of cyclized rings
Furanose (5-membered)
Pyranose (6-membered)
Alpha and beta anomeric positions in D-sugars
Alpha: trans to C6
Beta: cis to C6
L-sugars: switched
Sugar phosphates
One of the carbohydrate’s hydroxyl groups is converted to a phosphate ester
Deoxy sugars
Hydrogen replaces the hydroxyl in the parent sugar
Amino sugars
Amino group replaces a hydroxyl in the parent monosaccharide
Position of amino group is not always obvious, since it isn’t numbered (but often carbon #2)
Sugar alcohols
Carbonyl of parent sugar is reduced to an alcohol
Replace -ose with -itol
Sugar acids
Either C-1 aldehyde is oxidized to carboxylic acid or primary alcohol (highest carbon number) is oxidized to an acid
Disaccharides
Covalent linkage of 2 monosaccharides through a glycosidic bond at the anomeric carbon
Named in order with “free anomeric” sugar last
Glycosidic bonding is indicated using numbers separated by an arrow
Reducing sugars
Sugars with an aldehyde or a hemiacetal can be oxidized to an acid and can reduce other ions
2 types of polysaccharides
Homoglycans: 1 type of monomer
Heteroglycans: several types of monomers
Amylose
Type of starch (storage polysaccharide)
Smaller than amylopectin and glycogen
Alpha- (1 -> 4) glycosidic linkages
Amylopectin
Type of starch (storage polysaccharide and polymer of glucose)
Bigger than amylose, but smaller than glycogen
Amylose with alpha- (1 -> 6) branches every ~25 residues
Glycogen
Form of storage used in most animals
Main chain is alpha- (1 -> 4)
Alpha- (1 -> 6) linkages every 8-12 residues
Bigger than amylose or amylopectin
Cellulose
Linear polymer of glucose
Structural polysaccharide in plants
Unbranched, beta- (1 -> 4) glycosidic bonds
Highly rigid
Chitin
Structural polysaccharide in bugs and crustaceans
Linear polymer of N-acetylglucosamine
Beta- (1 -> 4) glycosidic bonds
Glycoconjugates
Polysaccharides covalently bound to proteins or peptides
Proteoglycans
Complexes of proteins and glycosaminoglycans
High surface area: attract water for connective tissue
Glycoproteins
Carbohydrates attached to proteins
Classified as N-linked (asparagine) or O-linked (serine)
Peptidoglycans
Polysaccharides linked to small peptides
Found in the cell walls of many types of bacteria: keeps cell in rigid shape by maintaining osmotic balance
