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7/31/2019 Ch. 19 Carbohydrates
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Ch. 19
Carbohydrates
Milbank High School
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Chapter Objectives
1. What are carbohydrates? What is thedifference between mono-, di-, andpolysaccharides?
2. What are the structures of the most commonlyoccurring monosaccharides? Be able to classifythem as aldoses or ketoses and as trioses,pentoses, or hexoses.
3. What is the difference between a D and an Lsugar?
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Chapter Objectives
4. What is mutarotation? How does itoccur?
5. What are the structures of sucrose,lactose, and maltose, the most commondisaccharides? What monosaccharidesmake up each of these disaccharides?
6. Compare and contrast starch, glycogen,and cellulose.
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What is Biochemistry?
The chemistry of molecules and reactionsfound in living organisms
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Carbohydrates
Carbon hydrates Compounds containing carbon, hydrogen, and
oxygen Starches and fibers (complex carbohydrates) Sugars Cellulose
Contain hydroxyl groups And either an aldehyde or ketone Known as polyhydroxy aldehydes or ketones
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Monosaccharides
Simple carbohydrates Cannot be further hydrolyzed
Contain 3-7 carbons Readily dissolve in water Can link together to form more complex
carbohydrates Disaccharides Trisaccharides Polysaccharides
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Sec. 19.1General Terminology and
Stereochemistry Named using IUPAC to name
monosaccarides Name the number of carbons, then add-ose Trios, tetrose, pentose, hexose etc
If aldehyde is attached: aldotetrose If ketone is attached: ketotetrose
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Common monosaccharides
Glucose Fructose
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Enantiomers
Molecules that are nonsuperimposablemirror images of each other
Have identical physical properties exceptone: They rotate plane-polarized light in opposite
directions
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Trioses
Simplest sugars Two enantiomers
D sugars L sugars
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Sec. 19.2Hexoses
Aldohexoses 16 isomers (8 enantiomeric pairs) 3 most common:
Glucose, mannose, galactose
Ketohexoses 8 isomers
fructose
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Glucose
Most abundant sugar in nature Fruits
grape sugar Dextrose b/c it is dextrorotatory
Carbs converted to glucose Produces energy for our cells
Circulating carbohydrate Blood sugar
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Glucose Cont
Synthetically made by the hydrolysis of starch Corn starch
corn sugar
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Mannose
Component of polysaccharide mannan Berries Vegetable ivory endosperm
Differs from glucose at only one point
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Galactose
Needed by human body for synthesis of lactose In mammary glands
Also important constituent of theglycolipids Occur in brain in myelin sheath of nerve cells brain sugar Differs from glucose at only one point
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Fructose
Only naturally occurring ketohexose Also similar structure to that of glucose
Found in honey (40%) Formed in prostate gland
Energy source for spermatozoa
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Artificial Sweeteners
High-intensity sweeteners Manufactured in place of mono- and
disaccharides Saccharin
1890s 500-700 times sweeter than sucrose Carcinogenic
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Artificial Sweeteners
Aspartame 1967 160 times sweeter than sucrose Used in diet soda
Sucralose 1998 600 times sweeter than sucrose Passes through body unchanged
S 19 3
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Sec. 19.3Cyclic Structures of
Monosaccharides
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Sec. 19.4Properties of Monosaccharides
Crystalline solids at room temperature Quite soluble in water
Converted to anions when Tollens andBenedicts reagents are used Used in simple and rapid diagnostic tests
for the presence of glucose in blood or urine
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Sec. 19.5Disaccharides
Composed of two monosaccharide units Joined when one monosaccharide reacts
with the hydroxyl group of a secondmonosaccharide
Forms a carbon-oxygen-carbon linkage glycosidic linkage
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Maltose
Occurs in sprouting grain Forms malt in the manufacture of beer
malt sugar
About 30% as sweet as sucrose Body cant utilize it directly
Must be broken down by enzymes
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Lactose
Milk sugar Occurs in the milk of humans, cows, and other
mammals
Human milk: 7.5% lactose Cows milk: 4.5% lactose Synthesized only by mammary tissue in nature
Commercial produced from whey (from cheese) 1/6 th as sweet as sucrose
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Lactose Intolerance Cont
Foods can be treated with lactase Lactaid
Tablets taken orally with dairy foods to assistin their digestion
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Sucrose
Beet sugar, cane sugar, table sugar, or just sugar
Largest selling pure organic compound inthe world
Obtained from sugar canes and beets Average American: 100 pounds of sucrose
every year
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Sucrose Cont
May cause cancer, heart disease,migraine headaches, hyperactivity inchildren, obesity, and tooth decay
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Sec. 19.6Polysaccharides
Most abundant carbs in nature Store energy and make up plant cells
High-molar mass Starch, glycogen, and cellulose
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Starch
Most important source of carbs in the humandiet
More than 50% of our carb intake
Granule form Storage
Potatoes: 15%
Wheat: 55% Corn: 65% Rice: 75%
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Starch Cont
Mixture of amylose and amylopectin Amylose: 60-300 glucose units per chain
Amylopectin: 300-6000 glucose units
Commercial starch
White powder Stamps, envelopes, labels (sticky upon wetting)
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Glycogen
animal starch Reserve carb of animals
All mammalian cells contain glycogen Liver and skeletal cells the most Used when fasting
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Cellulose
Fibrous carb found in all plants Cell walls
Most abundant of all carbs Makes up 50% of all carbon in thevegetable world
Much hydrogen bondinginsoluble inwater
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Cellulose Cont
Cant be digested by humans Herbivores contain special enzymes to
digest it and use it for energy Termites
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Dietary Fiber
Insoluble fiber (cellulose) Reduces risk of colon cancer and heart
disease (reduces cholesterol) ADA recommends 20-35 g a day
Most Americans get 14-15 g a day