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Chapter 8 (part 1)

Chapter 8 (part 1)

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Chapter 8 (part 1)

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  1. Chapter 8 (part 1) Carbohydrates

  2. Carbohydrates • Most abundant class of biological molecules on Earth • Originally produced through CO2 fixation during photosynthesis

  3. Roles of Carbohydrates • Energy storage (glycogen,starch) • Structural components (cellulose,chitin) • Cellular recognition • Carbohydrate derivatives include DNA, RNA, co-factors, glycoproteins, glycolipids

  4. Carbohydrates • Monosaccharides (simple sugars) cannot be broken down into simpler sugars under mild conditions • Oligosaccharides = "a few" - usually 2 to 10 • Polysaccharides are polymers of the simple sugars

  5. Monosaccharides • Polyhydroxy ketones (ketoses) and aldehydes (aldoses) • Aldoses and ketoses contain aldehyde and ketone functions, respectively • Ketose named for “equivalent aldose” + “ul” inserted • Triose, tetrose, etc. denotes number of carbons • Empirical formula = (CH2O)n

  6. Monosaccharides are chiral • Aldoses with 3C or more and ketoses with 4C or more are chiral • The number of chiral carbons present in a ketose is always one less than the number found in the same length aldose • Number of possible steroisomers = 2n (n = the number of chiral carbons)

  7. Stereochemistry • Enantiomers = mirror images • Pairs of isomers that have opposite configurations at one or more chiral centers but are NOT mirror images are diastereomers • Epimers = Two sugars that differ in configuration at only one chiral center

  8. Cyclization of aldose and ketoses introduces additional chiral center • Aldose sugars (glucose) can cyclize to form a cyclic hemiacetal • Ketose sugars (fructose) can cyclize to form a cyclic hemiketal

  9. Haworth Projections -OH up = beta -OH down = alpha 6 5 4 1 2 3 Anomeric carbon (most oxidized) For all non-anomeric carbons, -OH groups point down in Haworth projections if pointing right in Fischer projections

  10. Monosaccharides can cyclize to form Pyranose / Furanose forms a = 64% b = 36% a = 21.5% b = 58.5% a = 13.5% b = 6.5%

  11. Conformation of Monosaccharides Pyranose sugars not planar molecules, prefer to be in either of the two chair conformations.

  12. Reducing Sugars • When in the uncyclized form, monosaccharides act as reducing agents. • Free carbonyl group from aldoses or ketoses can reduce Cu2+ and Ag+ ions to insoluble products

  13. Derivatives of Monosaccharides

  14. Sugar Phosphates

  15. Deoxy Acids

  16. Amino Sugars

  17. Sugar alcohols

  18. Monosaccharide structures you need to know • Glucose • Fructose • Ribulose • Glyceraldehyde • Dihydroxyacetone