Carbohydrates -I-

1. CH2OH O H H H OH H OH HO H OH Carbohydrates -I- Energy molecules

2. General Characteristics • Carbohydrates = Carbon (C) + Hydrates (OH). • All carbohydrates are compounds composed of (at least) C, H, and O • The general formula for a carbohydrate is: (CH2O)n • Not all carbohydrates have this empirical formula (e.g. deoxysugars, aminosugars, etc.) • Carbohydrates are the most abundant compounds found in nature. • Produced by photosynthesis in plants from CO2, H2O and energy. • Are oxidized in living cells (respiration) to produce CO2, H2O, and energy.

4. Carbohydrate Functions Carbohydrates can be: • Sources of energy • Intermediates in the biosynthesis of other basic biomolecules (fats and proteins) • Structural tissues in plants and in microorganisms (cellulose, lignin, murein) • Involved in biological transport, cell-cell recognition, activation of growth factors, modulation of the immune system

5. Classification: Carbohydrates are placed in to one of three categories, depending on the number of monosaccharide units, or residues, they contain. • Monosaccharides, contain a single monosaccharide residue. • Oligosaccharides, contain 2 to 10 monosaccharide residues. • These include the disaccharides, which contain 2 monosaccharide residues. • Polysaccharides, which contain more than 10 monosaccharide residues. • These may contain thousands of monosaccharide residues.

6. Monosaccharides • Monosaccharides are polyhydroxyaldehydes or ketones. • Monosaccharides contain 3 to 7 carbon atoms.

7. Monosaccharides Monosaccharides are classified according to the number of carbons and whether they contain an aldehyde or ketone. • The “-ose” ending is used to designate carbohydrates.

8. Monosaccharides Monosaccharides contain chiral carbon atoms. • This is what accounts for the large number of different monosaccharides. • For each chiral carbon, n, a monosaccharide has 2nstereoisomers. • These will be divided among 2n/2 pairs of enantiomers. • Glucose contains 4 chiral carbons • Glucose has 24 = 16 stereoisomers • These stereoisomers can be grouped into 16/2 = 8 pairs of enantiomers.

9. Fischer projection: Monosaccharides Fischer projections are used to distinguish the different stereoisomers. • The letters D and L are used to distinguish between the members of a pair of enantiomers. • The D or L designation is based on the chiral carbon furthest from the carbonyl carbon.

10. Monosaccharides Important monosaccharides. • pentoses and hexoses are the most abundant Pentoses • D-ribose and D-2-deoxyribose are found in DNA, RNA and nucleotides such as FADH2 and NADH

11. Epimers • Pairs of monosaccharides different only inconfiguration around only one specific C-atom. • For example, glucose and galactose are C-4 epimers—their structures differ only in the position of the -OH group at carbon 4.

12. Monosaccharides Important monosaccharides. Hexoses • D-glucose (dextrose or blood surgar) - major metabolite and storage form of chemical energy. • D-galactose - combines with glucose to produce lactose (milk sugar) • D-fructose (fruit sugar) - major metabolite and sweetest tasting natural sugar. • fructose is a ketose

13. Monosaccharides Monosaccharide derivatives • Amino sugars. • One or more -OH’s are replaced with -NH2’s • Often these are acetylated to form amides. Arthritis relief??

14. Monosaccharides Monosaccharide derivatives • Carboxylic acid sugars. • The ketone, aldehyde, or primary alcohol is oxidized to a carboxylic acid.

15. β-D-sorbofuranose α-D-sorbofuranose Question: Shown below is the Fischer projection for sorbose Is the structure shown • D-sorbose • L-sorbose Draw and name the α and β ring forms for sorbose

16. α-L-galactopyranose β-L-galactopyranose Question: Shown to the right is the Fischer projection for galactose Is the structure shown • D-galactose • L-galactose Draw and name the α and β ring forms for galactose

17. إن الله وملائكتــه يصلــون على النبي يــأيــها الذيـن آمنوا صلــوا عليه وسلمـــوا تسليمـــا