Mathematics Used in Chemistry

1
Chapter 17Carbohydrates
Suggested Problems 4, 9, 21, 53, 61, 62, 63
2
Biochemistry

• Biochemistry is the study of the compounds and
  processes associated with living organisms
• Carbohydrates
• Lipids
• Proteins
• DNA

3
Important Functions of Carbohydrates

• To provide energy through their oxidation
• To supply carbon for the synthesis of cell
  components
• To serve as a stored form of chemical energy
• To form a part of the structural elements of some
  cells and tissues

4
Stereochemistry

• Isomers are molecules with the same formula but
  different atom connectivity
• Some isomers are mirror images but cannot be
  superimposed on each other
• These isomers are called enantiomers
• Must have four different groups on one carbon
  atom

5
Stereochemistry

• Many biomolecules exists as enantiomers

6
Stereochemistry

• A Fisher projection views each stereocenter from
  the convex side of the angle defined by the two
  in-plane bonds

7
Fisher Projections 2
I see the Bron my right
The methyl group is at the topand the ethyl
group is at the bottom
8
Stereochemistry

• Fisher projections

9
Stereochemistry
10
Carbohydrates

• Definition polyhydroxy aldehydes or ketones, or
  substances that yield such compounds upon
  hydrolysis
• Example

Aldehyde or Ketone?
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Classification of Carbohydrates

• Classified according to size
• Monosaccharide a single polyhydroxy aldehyde or
  ketone unit
• Disaccharide two monosaccharide units joined
  together

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Classification of Carbohydrates

• Classified according to size
• Oligosaccharide chain containing 3-10
  monosaccharide units
• Polysaccharide many monosaccharide units
  connected in long chains (can be thousands)

13
Monosaccharide Classification

• Is the monosaccharide a aldehyde (aldose) or a
  ketone (ketose)?
• How many carbon atoms are in the monosaccharide?

14
Monosaccharide Classification

• Classify the following according to functional
  group and carbon number

Glucose
Ribulose
aldohexose
ketopentanose
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Physical Properties of Monosaccharides

• Because of the many OH groups, they form
  hydrogen bonds with water molecules and are
  extremely water soluble.
• Most are called sugars because they taste sweet.

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Cyclic Monosaccharides

• All monosaccharides with at least five carbon
  atoms exist predominantly as cyclic hemiacetals
  and hemiketals.
• Anomers are stereoisomers that differ in the 3-D
  arrangement of groups at the anomeric carbon of
  an acetal, ketal, hemiacetal, or hemiketal group.

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Cyclic Monosaccharides

• A Haworth structure can be used to depict the ?
  (-OH on the anomeric carbon pointing down) and ?
  (-OH on the anomeric carbon pointing up) anomers
  of a monosaccharide.

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Cyclic Monosaccharides

• In solution, Glucose can take 3 forms

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Rxns of Monosaccharides

• Oxidation
• All monosaccharides are reducing sugars and can
  be oxidized
• Benedicts reagent tests for the presence of
  reducing sugars
• Cu2O precipitate is positive for reducing sugar

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Rxns of Monosaccharides

• Reducing sugar Cu2 ? oxidized compound Cu2O

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Rxns of Monosaccharides

• Formation of Phosphate esters
• The OH groups of monosaccharides can behave as
  alcohols and react with acids (especially
  phosphoric acid) to form esters

2-deoxyribose-5-phosphate
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Rxns of Monosaccharides

• Glycoside Formation
• Monosaccharides (hemiacetals, hemiketals) readily
  react with alcohols to form acetals and ketals
• Acetals/Ketals are more stable than
  hemiacetals/hemiketals

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Rxns of Monosaccharides

• Glycosidic linkages form the basis for
  dissacharides and polysaccharides
• Cyclic hemiacetal/hemiketal of a monosaccharide
  reactions with OH group of another monosaccharide

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Important Monosaccharides

• Ribose and 2-deoxyribose
• Found in RNA, DNA as phosphate esters

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Important Monosaccharides

• Glucose
• Most nutritionally important monosaccharide
• Also called dextrose or blood sugar
• Galactose
• Component of lactose (milk sugar)

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Important Monosaccharides

• Fructose
• Sweetest of monosaccharides
• Also called levulose or fruit sugar

27
Disaccharides

• Disaccharides are formed by glycosidic linkages
• Glycosidic linkages identified by
• Configuration (a,ß) of the linkage for ANY
  anomeric carbon joined in the linkage

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Important Disaccharides

• Maltose
• Composed of two a-D-glucose units
• Formed from the hydrolysis of starch

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Important Disaccharides

• Lactose
• Compose of galactose and glucose linked ß (1?4)
• 5 (by weight) of cows milk

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Important Disaccharides

• Sucrose
• Composed of a a-D-glucose unit and a ß-D-fructose
  unit
• Linkage is a1?ß2
• Enzymes see it as an alpha linkage
• Very abundant in the plant world

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Disaccharides

• Which disaccharides are reducing sugars?

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Polysaccharides

• Carbohydrate Polymers

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Important Polysaccharides

• Starch
• Two forms
• amylose (10-20)
• Amylopectin (80-90)
• Test for starch relies on the reaction of iodine
  (I2) with amylose

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Important Polysaccharides

• Amylose
• Long, straight chains of glucose
• Flexible to twist into helix

35
Important Polysaccharides

• Amylopectin
• Branched polymer
• a (1?4) linkages for straight parts
• a (1?6) for branches
• 24-30 glucose units between branches

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Important Polysaccharides

• Glycogen
• Glucose storage for animals, particularly in the
  liver and muscles
• Similar to amylopectin
• Highly branched polymer of glucose with a (1?4)
  and a (1?6) linkages
• 8 to 12 glucose units between branch points

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Important Polysaccharides

• Cellulose
• Linear glucose polymer like amylose but hasß
  (1?4) linkages
• Extended straight chains rather than helixes
• Found in plant cell walls and is a constituent of
  dietary fiber
• Digested only by bacteria