Chapter 18 Carbohydrates

Goals Distinguish and describe mono, di, oligo, and polysaccharides Classify and name monosaccharides Know D aldose and ketose Draw cyclic hemiacetals Describe photosynthesis Know mutarotation, oxidation, acetal formation

Beginning of Biochemistry Biomolecules – 3 aspects to consider

Biomolecules Four main families –Carbohydrates –Nucleic acids

Carbohydrates Called saccharides Functions

Where found Sugar Wood

Classifications Polyhydroxyketone (ketose) Monosaccharides

Naming IUPAC is not used… long and difficult names Most names are common names and end in

Structure Aldose Ketose

Classifying 5 carbon with aldehyde group 4 carbon with a ketone group See figures 18.1 and 18.2 p 528-9

D or L? Chiral recognition and the use of enzymes in organisms selectively produces the D form of the –ose L form is not produced in nature

Important monosaccharides D-Glucose D-Fructose D-Galactose

Monosaccharides D-Ribose D-Xylose D-glyderaldehyde and D-hydroxyacetone

Cyclic Hemiacetals Presence of both carbonyl carbon and hydroxyl group allows for cyclic structure The closed ring is called a Page 531

Cyclic hemiacetals Unlike straight chain hemiacetals, cyclics are Isomeric difference is important for function

Cyclics Ketohexoses form –Addition of an –OH to C5 –Two anomers are formed Haworth projections (figures 18.3 and18.4)

Mutarotation All aqueous solutions of D-glucose Isolate alpha and make a solution, after time the mixture Same process for each anomer Mutarotation is change in specific rotation of light to the equilibrium value

Oxidation of aldose Oxidation of open structure, not hemiacetal Governed by

Oxidation Alpha-hydroxy ketones Aldoses and ketoses are called “Reducing Sugars” –Reduce Cu 2+ to Cu +

Glycosides Formation of an acetal –Page 537 –Alpha and beta glycosides depending on which anomer is converted –In organisms,

Glycosides Acetals of carbos are Carbons are connected by a glycosidic linkage. Two types: – Nature is stereospecific – This bond forms di and polysaccharides

Monosaccharide derivatives

Disaccharides Two monosaccharides connected with glycosidic linkage Characterized by:

Four Important Maltose: Cellobiose: Lactose: Sucrose:

Digestion of Carbohydrates Large saccharides They must be broken down

Polysaccharides Large numbers of monosaccharide residues

Polysaccharides Differ from each other in many ways

Starch Amylose: Amylopectin: branched D-glucose Glycogen:

Digestion of Starch Digested to D-glucose in intestines by amylase Neither Dextrin is digested by

Starch Digestion Some Some polymerized Extra glucose (beyond needed) When needed,

Cellulose Structural polysaccharide Most abundant organic compound in biosphere Cotton is nearly pure cellulose Linear polyglucose: B(1-4) linkages

Starch and Cellulose A(1-4) Add water? Food for humans Links not allow for extended conformations Form helices fig B(1-4) Add water? Not good food Links allow for extended 3D conformations Fig p 547

Cellulose - uses Build houses Fabrics – Paper Starting point

Cell recognition Process that ensures cells interact as they should within the organism Due to presence of Usually

Photosynthesis Source of energy for non-plant life and all organic molecules used Process of carbon fixation

Photosynthesis Plants convert glucose and other monosaccharides to: