Chapter 14

sucrose and artificial sweetners

sucrose, the disaccharide found in sugarcane and the compound generally referred to as "sugar", is the most common disaccharide in nature contains one glucose ring and one fructose ring unlike maltose and lactose, which only contain six-membered rings, sucrose contains one six membered ring and one fiver membered ring

artificial sweetners

aspartame, saccharin and sucralose much sweeter than sucrose so only a small amount of each compound is needed to achieve the same level of perceived sweetness

photosynthesis

carbs are storehouses of chemical energy and are synthesized in green plants and algae through photosynthesis (process that uses solar energy to convert CO2 and H2O into glucose and oxygen) plants store glucose in the form of starch and cellulose energy stored in glucose bonds is released when glucose is metabolized, oxidation of glucose is a multistep process that forms carbon dioxide, water and a great deal of energy the metabolism of lipids provides more energy per gram than the metabolism of carbs, glucose is the preferred source when a burst of energy is needed during exercise

disaccharides

carbs composed of two monosaccharides formed when a hydroxyl group of one monosaccharide reacts with a hydroxyl group of a second monosaccharide the new C-O bond that joins the two rings together is called a glycosidic linkage the carbon in a glycosidic linkage is bonded to two O atoms- one O atom is part of a ring, and the other O atom joins the two rings together

carbohydrates

commonly referred to as sugars and starches, are polyhydroxy aldehydes and ketones, or compounds that can be hydrolyzed to them carbs can be simple or complex, theyre the largest group of organic molecules in nature: approximately 50% of earths biomass

disaccharides

composed of 2 monosaccharides joined together examples: lactose, principal carbs in milk contain no carbonyl groups but are hydrolyzed to simple monosaccharide that contain an aldehyde or a ketone

universal recipients

individuals with type AB blood are universal recipients because they can receive any type of blood

universal donor

individuals with type O blood are universal donor because it can be given to individuals of any blood type

glycosidic linkage

joins the 2 monosaccharides in a disaccharide- can be oriented in two different ways an alpha glycoside has the glycosidic linkage oriented down the beta glycoside has the glycosidic linkage oriented up

insulin

protein produced in the pancreas, regulates blood glucose levels- when glucose concentration increases after eating, insulin stimulates the uptake of glucose in tissue and its conversion to glycogen patients with diabetes produce insufficient insulin to adequately regulate blood glucose levels, and the concentration of glucose rises individuals with poorly controlled diabetes can develop significant complications such as cardiobascular disease, chronic renal failure and blindness

monosaccharides

simples sugars, are the simplest carb examples: glucose and fructose- 2 major constituents of honey

starch

starch is the main carb found in the seeds and roots of plants corn, rice, wheat and potatoes are common food that contain a great deal of starch starch is a polymer composed of repeating glucose units joined in alpha glycosidic linkages, water soluble 2 common forms of starch: amylose and amylopectin

reactions of monosaccharides

the aldehyde carbonyl group of a monosaccharide undergoes two common reactions- reduction to an alcohol and oxidation to a carboxylic acid

monitoring glucose levels

to make sure that their blood glucose levels are in the proper range, individuals with diabetes frequently measure the concentration of glucose in their blood common method for carrying out this procedure today involves the oxidation of glucose to gluconic acid using the enzyme glucose oxidase in the presence od glucose oxidase, oxygen in the air oxidizes the aldehyde of the glucose to a caroxylic acid the oxygen in turn is reduced to hydrogen peroxide in the first generation of meters for glucose monitoring, the hydrogen peroxide produced in this reaction was allowed to react with another organic compound to produce a colored product intensity of the colored product was then correlated to the amount of glucose in the blood

amylose

which comprises about 20% of starch molecules, has an unbranched skeleton of glucose molecules with alpha glycoside bonds- because of this linkage, an amylose chain adopts a helical arrangement- giving it a very different 3 D shape from the linear chains of cellulose

the cyclic forms of monosaccharides

OH group on C5 reacts with aldehyde carbonyl to form a six membered ring with a new chirality center yields two isomers: one with the OH group above the chirality center and one below the isomer called alpha D glucose has the OH group on the new chirality center drawn down Beta D glucose has the OH group on the new chirality center drawn up (these are hawthorn projections)

Glucose

also called dextrose, is the sugar referred to when blood sugar is measured, the most abundant monosaccharide building block for the polysaccharides starch and cellulose carb that is transported in the bloodstream, provides energy for cells when it is metabolized normal blood glucose levels are in the range of 70-110 mg/dL

amylopectin

comprises about 80% of starch molecules, consists of a backbone of glucose units joined in alpha glycosidic bonds, but also contain considerable branching along the chain: linear linkages of amylopectin are formed by alpha glycoside bonds similar to amylose both forms of starch are water soluble since OH groups in these starch molecules are not buried in a 3 D network- available to hydrogen bond both amylose and amylopectin are hydrolyzed to glucose with cleavage of the glycosidic bonds

polysaccharides

contain three or more monosaccharides joined together most prevalent: starch, cellulose and glycogen each consist of repeating glucose units joined by glycosidic bonds

simplest ketose

dihydroxyacetone

carbohydrate and blood types

each blood type is characterized by a different polysaccharide that is covalently bonded to a membrane protein of the red blood cells there are three different types of carbohydrate sequences (blood type AB contains the sequences for both A and B type) because the blood of an individual may contain antibodies to another blood type, the types of blood that can be given to a patient are limited an individual with type B produces antibodies to type A type AB blood contains no antibodies to other blood types, while type O contains antibodies to both type A and B

monosaccharides with more than one chirality center

fischer projection formulas are also used for compounds like aldohexoses that contain several chirality centers ex: glucose contains 4 chirality centers to convert the molecule to a fischer projection, the molecule is drawn with a vertical carbon skeleton with the aldehyde at the top, the horizontal bonds are assumed to come forward the letters D and L are used to label all monosaccharides, even those with many chirality centers

cellulose

found in cell walls of nearly all plants where it gives support and rigidity to wood, plant stems and grass wood, cotton and flax are composed largely of cellulose cellulose= unbranched polymer composed of repeating glucose joined in a beta glycosidic linkage, create long linear chains of cellulose molecules that stack in sheets, making it impossible for cellulose to be soluble in water in some cells, cellulose is hydrolyzed by an enzyme that cleaves all of the beta glycoside bonds: forming glucose humans do not possess this enzyme and therefore cannot digest cellulose- animals do makes up much of our insoluble fiber, helps us eliminate waste more readily

solubility of monosaccharides

glucose is water soluble so it can be quickly and easily transported through the bloodstream to tissues

simplest aldose

glyceraldehyde

glycogen

glycogen is the major form in which polysaccharides are stored in animals, polymer of glucose containing alpha glycosidic bonds, has a branched structure similar to amylopectin, but the branching is much more extensive stored principally in the liver and muscles when glucose is needed for energy in the cell, glucose units are hydrolyzed from the ends of the glycogen polymer and then further metabolized with the release of energy because glycogen has a highly branched structure, there are many glucose units at the ends of the branches that can easily be cleaves whenever the body needs them

polysaccharides

have three or more monosaccharides joined together example: starch, the main carb found in the seeds and roots of plants polysaccharides are hydrolyzed to simple monosaccharides that contain carbonyl groups

blood type

human blood is classified into one of four types- A,B, AB and O an individuals blood type is determined by 3 or 4 monosaccharides attached to a membrane protein of red blood cells each blood type is associated with a different carbohydrate structure the short polysaccharide chains distinguish one type of red blood cell from another, and signal the cells about foreign viruses, bacteria and other agents when a foreign substance enter the blood, the bodys immune system uses antibodies to attack and destroy the invading substances so that it does not harm the host organism

lactose intolerance

lactose is the principal disaccharide found in milk from both humans and cows unlike many mono and disaccharides, lactose is not appreciably sweet lactose consists of one glucose and one galactose bonded by a beta glycosidic linkage lactose is digested in the body by first cleavingg the beta bond using the enzyme lactase individuals who are lactose intolerant no longer produce lactase and so lactose cannot be properly digested, causing abdominal cramps and diarrhea lactose intolerance= especially prevalent in asian and african populations whose diets have not included milk

reduction of the aldehyde carbonyl group

like the double bond in an alkene, the double bond in the carbonyl of an aldose reacts with hydrogen in the presence of palladium metal catalyst this product, an alcohol called alditol, is sometimes referred to as a "sugar alcohol" reduction of D glucose with H2 and Pd yields glucitol, commonly called sorbitol reaction is a reduction, since the number of carbon- oxygen bonds decrease sorbitol is used as a sweeting agent in a variety of candies and gum

maltose

maltose is a disaccharide formed from 2 molecules of glucose it is found in grains such as barley, product of hydrolysis of starch each ring in maltose in numbered beginning at the carbon bonded to two oxygen atoms in maltose, the glycosidic linkage joins C1 of one ring to C4 of another ring

fructose

one of 2 monosaccharides that form the disaccharide sucrose ketohexose found in honey and is almost twice as sweet as normal table sugar with about the same number of calories per gram

galactose

one of the two monosaccharides that for the disaccharide lactose, individuals with galactosemia lack an enzyme needed to metabolize galactose galactose accumulates, causing a variety of physical problems such as cataracts, cirrhosis and mental retardation galactosemia can be detected in newborn screening, and affected infant must be given soy-based formula to avoid all products with lactose

oxidation of the aldehyde carbonyl group

the aldehyde carbonyl of an aldose is easily oxidized with a variety of reagents to form a carboxyl group, yielding an aldonic acid this results in a carboxylic acid as it has one more C-O bond than the starting aldehyde carbs that are oxidized by benedicts reagent are called reducing sugars those that do not react with benedicts reagent are called nonreducing sugars: all aldoses are reducing sugars

D and L monosaccharides

the configuration of the chirality center farthest from the carbonyl group determines whether a monosaccharide is D or L a D monosaccharide has the OH group on the chirality center farthest from the carbonyl on the right an L monosaccharide has the OH group on the chirality center farthest from the carbonyl on the left L monosaccharide is not naturally occuring glucose and all other naturally occuring sugars are D sugars L Glucose, a compound that does not occur in nature is the enantiomer of D glucose

hydrolysis of a disaccharide

the hydrolysis of a disaccharide cleaves the C-O glycosidic linkage and forms two monosaccharides example: the hydrolysis of maltose yields two molecules of glucose

common monosaccharides

the most common monosaccharides in nature are the aldohexoses D-Glucose and D-galactose and ketohexose D- Fructose

monosaccharides

the simplest carb, generally have 3 to 6 carbon atoms in the chain with a carbonyl group at either the terminal carbon, number C1 or the adjacent carbon to it in most carbohydrates, each of the remaining carbon atoms has a hydroxy group monosaccharides with a carbonyl group at C1 are aldehydes called aldoses monosaccharides with carbonyl group at C2 are ketones called ketoses glucose is the most prevalent aldose