Includes sugars and their polymers Macromolecules Part I: Carbohydrates: Includes sugars and their polymers

Four types of Carbohydrates Monosaccharides - simple sugars with multiple OH groups. Based on number of carbons (3, 4, 5, 6), a monosaccharide is a triose, tetrose, pentose or hexose Disaccharides - 2 monosaccharides covalently linked Oligosaccharides - a few monosaccharides covalently linked Polysaccharides - polymers consisting of chains of monosaccharide or disaccharide units (few 100 to 1000’s)

? Carbohydrates are composed of the following basic monomer: Monosaccharides generally have molecular formulas that are some multiple of CH2O [glucose = C6H12O6 which is ___ x CH2O]

Glucose Glucose is of central importance There is a ________ group attached to each carbon, except one This one carbon is double bonded to an oxygen to form a __________ group

? Monosaccharides Which functional group? Aldoses (e.g., glucose) have an aldehyde group at one end. Ketoses (e.g., fructose) have a ketone group, usually at C2.

? α- glucose β- glucose Pentoses and hexoses can cyclize as the ketone or aldehyde reacts with an OH (the double bond in the carbonyl group breaks to form 2 single bonds). These representations of the cyclic sugars are called Haworth projections.

α- glucose β- glucose Cyclization of glucose produces a new asymmetric center at C1 (C1 = Carbon #1). The 2 isomers are called anomers, a & b. To distinguish between the two anomers, we use the a & b symbols to indicate how the OH group on the anomeric carbon (C1) is oriented: a (OH below the ring) b (OH above the ring)

What happens if you eat too many carbs? If our body does not use all the digested carbohydrates, it will turn them into lipids for fat storage  The key is moderation!

i.e. glucose-OH + HO-glucose  glucose-O-glucose + H2O ? Glycosidic Bonds What type of reaction? The anomeric hydroxyl and a hydroxyl of another sugar or some other compound can join together, spitting out water to form a glycosidic bond: R-OH + HO-R'  R-O-R' + H2O i.e. glucose-OH + HO-glucose  glucose-O-glucose + H2O Glycosidic bond

Condensation (Dehydration synthesis) ? Condensation (Dehydration synthesis)

? Hydrolysis

? Disaccharides: Maltose, a cleavage product of starch, is a disaccharide with α(1-4) glycosidic link between the C1 OH & C4 OH of 2 glucoses. Maltose is important in brewing beer! Indicates which carbons are involved in the linkage (Important to know how the monomers are oriented)

? Other disaccharides include: Sucrose, common table sugar, has a glycosidic bond linking the anomeric hydroxyls of glucose & fructose. Because the configuration at the anomeric C of glucose is a (O points down from ring), the linkage is a(12). Lactose, the sugar that is in milk, is composed of galactose & glucose, with b(14) linkage from the anomeric OH of galactose. Its full name is b-D-galactopyranosyl-(1 4)-a-D-glucopyranose

What is lactose intolerance? Lactose intolerance is an inability to digest and absorb lactose (the sugar in milk) when milk or products containing milk are drunk or eaten. What causes lactose intolerance? Lactose must be split into glucose and galactose before they can be absorbed by the cells lining the small intestine The enzyme that splits lactose is called lactase Lactose intolerance is caused by reduced or absent activity of lactase that prevents the splitting of lactose (lactase deficiency). Lactase deficiency may due to congenital, secondary or developmental causes

Polysaccharides Some are used for storage material and hydrolyzed as needed to provide free sugars for energy Others serve as building material for structures or as protection

Polysaccharides – Storage Types ? Polysaccharides – Storage Types Plants store glucose as amylose or amylopectin – made entirely of glucose polymers; collectively called starch. Amylose is a glucose polymer with a(14) linkages. It adopts a helical conformation. The end of the polysaccharide with an anomeric C1 not involved in a glycosidic bond is called the reducing end.

? Amylopectin is a glucose polymer with mainly a(14) linkages, but it also has branches formed by a(16) linkages. Branches are generally longer than shown above. The branches produce a compact structure & provide multiple chain ends at which enzymatic cleavage can occur.

? Glycogen, the glucose storage polymer in animals, is similar in structure to amylopectin (it is extensively branched). But glycogen has more a(16) branches. The highly branched structure permits rapid release of glucose from glycogen stores, e.g., in muscle during exercise (also stored in the liver). The ability to rapidly mobilize glucose is more essential to animals than to plants.

? Cellulose, a major constituent of the tough plant cell walls, consists of long linear chains of glucose with b(1®4) linkages. Every other glucose is flipped over, due to the b linkages. This promotes intra-chain and inter-chain H-bonds and Aside  Van der Waals interactions, that cause cellulose chains to be straight & rigid, and pack with a crystalline arrangement in thick bundles called microfibrils. Botany online website

Polysaccharides: Cellulose No mammal makes the necessary enzymes to break down cellulose even though it is unbranched Those mammals that eat a lot of cellulose, like cows, need to keep symbiotic bacteria in their digestive tracks to help them digest the cellulose If we could be somehow given the gene to make enzymes to digest cellulose, then we could get nutrition from eating grass However, it is still important we include cellulose in our diet because it stimulates secretion of mucus from the lining of the digestive tract.

Polysaccharides: Chitin Chitin is used by arthropods to build their exoskeleton Notice that the monomer includes an _________ group so we call it an _______ sugar

Some Functions Glucose is vital to all organisms as a major cellular fuel source (respiration & photosynthesis) Lectins are glycoproteins (found where?) that recognize and bind to specific oligosaccharides Concanavalin A and wheat germ agglutinin are plant lectins that have been useful research tools Mannan-binding lectin (MBL) is a glycoprotein found in blood plasma that associates with cell surface carbohydrates of disease-causing microorganisms, promoting phagocytosis of these organisms as part of the immune response

Brown or white? raw sugar does retain some of the natural mineral and vitamin content in sugarcane juice, but not in significant amount

What about sucralose? Sucralose is approximately 600 times as sweet as sucrose (table sugar), twice as sweet as saccharin, and four times as sweet as aspartame Unlike aspartame, it is stable under heat and over a broad range of pH conditions and can be used in baking or in products that require a longer shelf life Sucralose has been accepted by several national and international food safety regulatory bodies, including the FDA, and Joint Food and Agriculture Organization/WHO Splenda usually contains 95% dextrose (the stereoisomer of glucose), which the body readily metabolizes  Splenda is recognized as safe to ingest as a diabetic sugar substitute