Carbohydrates What are they? –Sugars, starches & much more –Most abundant molecules on Earth –End products of photosynthesis

Carbohydrates Functional Roles –Carbohydrate polymers act as energy storage molecules –Cell walls and protective coatings –Cell recognition and interaction –Part of DNA, RNA, coenzymes

Classifications Monosaccharides –Smallest unit of carbohydrate structure –Hydrates of carbon (CH 2 O) n n = 3-9 Most common n = 5-6 Oligosaccharides –Polymers of 2-20 monosaccharides –Most common – disaccharides (2 monosaccharides

Polysaccharides –Polymers of many (usually >20) monosaccharides

Other Definitions Homoglycan – a polymer of identical monosaccharides Heteroglycans – a polymer of different monosaccharides (note: glycan is a term for carbohydrate polymers)

Glycoconjugates – carbohydrate derivatives –One or more carbohydrate chains covalently linked to peptide, proteins or lipids

More Definitions Stereoisomers – compounds that have the same molecular formula but different arrangements of their atoms in space Enantiomers – 2 stereoisomers that are mirror images of one another Diastereomers – 2 stereoisomers that are not mirror images of one another

Chiral Carbon- a carbon atom with 4 different groups bonded to it Epimers – molecules that differ in configuration at only one of several chiral centers

Monosaccharides Water-soluble, white, crystalline solids with a sweet taste Are polyhydroxy alcohols with at least 3 carbons

Two Types –Aldoses Contain an aldehyde on C 1 –Ketoses Contain a ketone, usually on C2 Smallest monosaccharides - trioses

Glyceraldehyde has 2 Forms It contains one chiral carbon – is optically active D-form rotates polarized light to the right L-form rotates polarized light to the left

In solution, monosaccharides exist in cyclic conformations Carbonyl carbons react with a hydroxyl group to produce: –Pyranose – a 6 membered ring –Furanose – a 5 membered ring The carbon attached to 2 O’s is called an anomeric carbon – can be alpha or beta

Haworth Projections A ring structure The ring is projected as lying perpendicular to the page Anomeric Carbon is on right or top OH’s on right are drawn down OH’s on left are drawn up

On anomeric carbon –Alpha configuration – OH is down –Beta configuration – OH is up

Other Furanose Conformations Envelope – one of the five ring atoms is out-of-plane & others are coplanar Twist – two of the five ring atoms are out-of-plane, one on either side of the plane formed by the other 3 atoms

Other Pyranose Conformations Chair – –Most stable – minimize steric hindrance –Substituents may be: Axial (above or below plane of ring) Equatorial (in the plane of the ring) Boat –

Derivatives of Monosaccharides Sugar Phosphates –Phosphate ester of one of the –OH groups –Often on the terminal carbon –Important in glucose metabolism (e.g., glucose 6-phosphate, glucose 1- phosphate)

Derivatives of Monosaccharides DeoxySugars –A hydrogen atom replaces a hydroxyl group –Very important in DNA synthesis (e.g., deoxyribose) –L-Fucose (6-deoxy-L-galactose) is common in polysaccharides

Derivatives of Monosaccharides Amino Sugars –One of the hydroxyl groups in a monosaccharide is replaced by: Amino group Acetylated amino group Important in glycoconjugates

N-Acetylneuraminic acid (NeuNAc) Starts with N-acetylmannosamine and pyruvate Cyclizes to a pyranose in a unusual way – carbonyl group at C-2 (from pyruvate) reacts with –OH at C-6 NeuNAc & its derivatives = sialic acids Important in glycoproteins

Derivatives of Monosaccharides Sugar Alcohols A carbonyl oxygen is reduced to an -OH

Derivatives of Monosaccharides Sugar Acids Derived from aldoses by either: oxidation of the aldehyde carbon oxidation of the highest numbered carbon