Cyclic Structures of Monosaccharides Chapter 14.3 Cyclic Structures of Monosaccharides

Monosaccharides in Nature The linear form of monosaccharides is instable - only 1% C5 and C6 carbs form Hemiacetal or cyclical form, ringform – 99% Sugars open and close randomly, frequently Intermolecular rearrangement

Hemiacetals Glucose: Hydroxyl group connects: C5 → C1 forming a 1,5 ether linkage. Not a dehydration but a rearrangement!!!

cyclization of glucose Cyclization of glucose B Hayworth projection

Hayworth Structure of Glucose

C1 :non-chiral in linear form but chiral in ring: labeled α or β

Numbering Carbons on Hemiacetals Always start on the right hand side 1,5 Ether Linkage

Cyclic Structure of Galactose Galactose is an aldohexose that differs from glucose only with the –OH group on carbon 4 With formation of a new hydroxyl group on carbon 1 – galactose also exists in α & β forms D-Galactose α-Galactose β-Galactose

Cyclic Structure of Fructose Fructose is a ketohexose: C5 reacts with ketone group C2 Smaller ring: pentagon

Fructose Ring numbering 2,5-ether linkage

Chapter 14.5 Disaccharides

1. Linking Monosaccharides together Monosaccharides can react with each other to form di- and polysaccharides (only ringforms can do that!) Dehydration Rx: involving the OH groups of two sugars, splitting out of a water molecule Formation of an ether linkage called glycosidic bond ( in sugars only!) Problem: which OH-groups are reacting? There are many….

Glycosidic bond formation

Naming of Glycosidic Bonds: Maltose Carbon # of first sugar connected to Carbon # number of second sugar Maltose: C1 is connected to C4 C1 is also in α position Writing conventions: α (1,4) glycosidic bond or alpha (1-4) “

More examples

Other glycosidic bonds beta (1-4) glycosidic bond

3 Disaccharides you need to know Maltose – malt sugar Lactose – milk sugar Sucrose - table sugar Generally, a disaccharide is characterized by…. Monosaccharide components glycosidic bonds

Maltose Monomers: 1. α-D-Glucose 2.α or β-D-Glucose Glycosidic bond: α (1-4) Creating two chiral versions of Maltose β Maltose α Maltose β-D-Maltose α-D-Maltose α/β of maltose is determined by the C1 position of second sugar

What’s Maltose – Malt Sugar Obtained from the hydrolysis of starch Used in cereals, candies, and brewing of beverages

Lactose Monomers: β-D-galactose with α-/β-D-glucose Glycosidic bond: β (1-4) Creating two chiral versions of Lactose β-D-Lactose α-D -Lactose

Lactose Makes up 6-8% of human milk and 4-5% of cow’s milk Lactose intolerance: lack of the enzyme lactase that splits disaccharide during digestion Adult Mammals stop expressing the lactase gene – exception: many adult humans have developed a lactose tolerance (microevolution) but depends on ethnicity

Sucrose Monomers: α-D-glucose and β-D-fructose Glycosidic bond: α,β (1,2) Creating only one form of D-Sucrose!!!

Sucrose Commercial sugar, obtained from sugar beets and sugar cane

Warm up 1. Identify the Carb class 2. Identify the monosaccharide components 3. Identify the glycosidic bond 4. Common Name Lactulose 2 1

Chapter 14.6 Polysaccharides

Polysaccharides A polymer of many monosaccharides joined together: glycosidic bd Important polysaccharides: Amylose/Amylopectin –plant starch Glycogen – animal starch Cellulose – plant fibers Monomers: all D-glucose but different glycosidic bonds

Amylose/Amylopectin Common name starches glucose storage in plant seeds, tubers etc Found in grains, potatoes, beans, fruits Soluble in water Commercial Starch: mixture amylose 20% and amylopectin 80%

Amylose Monomer: α-D-glucose (about 200-4000) Glycosidic bond: α (1,4) GB Enzyme breaking it: Amylase Structure: Long helical chain

Amylopectin Monomer: α, D-Glucose Glycosidic Bond: α (1,4) and α (1,6) GB (every 25 glucose monomers) Enzyme breaking it: amylase isozymes “Branched starch”

Glycogen Animal starch Storage of glucose in the liver Similar to amylopectin only more branches (every 10-15 glucose molecules)

Cellulose Monomers: β,D-glucose Glycosidic bond: β1,4-glycosidic bonds Enzyme breaking it: Cellulase Insoluble in water straight strands, found in the cell wall of plants, make plant stalks rigid and strong Humans, animal, plants DO NOT HAVE the enzyme cellulase only bacteria living in the guts of ruminants have cellulase

Cellulose Cotton, wood

Digestion of Cellulose Grazing animals and termites harbor e-coli who digest cellulose for them In humans cellulose helps absorb toxins from digestion of proteins to maintain a healthy digestive system

Carbohydrates in Our Diet

Hydrolysis Chemical reaction to separate polymers by inserting a water molecule