Carbohydrates

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Carbohydrates
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Carbohydrates

• Composed of the elements C, H, O
• They are hydrates of carbon
• Carbon H2O
• Empirical formula CH2O
• CHO ratio is 121
• Contain many hydroxyl groups
• Contain either an aldehyde or ketone
• Polar ( hydrophilic)

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Types of carbohydrates

• Monosaccharide
• Disaccharides
• Polysaccharides

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Monosaccharide

• Contain 3 - 7 carbon atoms
• Empirical formula (C1H2O1)n
• if n3    C3H6O3
• if n5    C5H10O5
• if n6    C6H12O6

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Naming Monosaccharides

• Most common 3, 5, 6 Carbons
• 3 Carbons Triose
• 5 Carbons Pentose
• 6 Carbons Hexose
• The ending -ose denotes a carbohydrate.
• Simple sugars (monosaccharides) contain one
  aldehyde or ketone
• If has a ketone group, it can be called a ketose
• If has an aldehyde group, it can be called an
  aldose

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Trioses

• Glyceraldehyde is a triose and an aldose, thus it
  is a aldotriose.

• Dihydroxyacetone is a triose and a ketose, thus
  it is a ketotriose.

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Pentoses

• Ribose and deoxyribose are both pentoses and
  aldoses, or aldopentoses.

• Ribose and deoxyribose differ around carbon 2.

deoxyribose
ribose
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Hexoses

• Glucose is an aldohexose

• Fructose is a ketohexose

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Glucose and fructose are structural isomers

• They have identical molecular formulas
• But the atoms arranged differently.
• Fructose is a ketohexose
• Glucose is an aldohexose
• See previous slide

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Enantiomers ( Stereoisomers)
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Glucose and galactose are enantiomers (
stereoisomers)

• Both are aldohexoses.
• They have identical molecular formulas,
• But Carbon 4 are mirror images of each other

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Hexoses

• In solution a hexose will form a ring.
• To assume this structure
• Carbon 1 forms a covalent bond with the oxygen on
  carbon 5
• The doubled bonded oxygen on carbon 1 accepts a
  hydrogen atom and is reduced to an alcohol (-OH).
  

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Glucose Ring Formation
a D-glucose
D-glucose
OH
ß D-glucose
OH
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a - and ß -glucose

• a -Glucose (alpha) -OH is on the opposite side
  of the ring as the -CH2OH.
• ß -Glucose (beta) -OH is on the same side of the
  ring as the -CH2OH.
• Remember ß balloon up
• See previous slide

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Disaccharides

• Two (2) monosaccharide rings joined by a
  glycoside linkage (a.k.a. glycosidic bond)
• mono mono ---gt mono--mono H20
                                    (disaccharide)
• Look familiar??
• Formed by a condensation rxn.
• Examples of disaccharides
• maltose, sucrose, lactose

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Disaccharides
Sucrose
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Hydrolysis of Disaccharides

• Maltose 1. Maltose H2O ---gt glucose glucose
  2. enzyme in this case maltase 3. Enzymes
  end in -ase
• Sucrose 1. Sucrose H2O --gt glucose fructose
  2. sucrase
• Hydrolysis of Lactose 1. Lactose H2O --gt
  galactose glucose 2. lactase

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Polysaccharides

• Repeating units of simple sugars
  (monosaccharides) joined by glycoside linkages.
• The sugar is usually glucose.

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Cellulose

• Is a homopolymer of glucose.
• Joined by ß -glycoside linkages
• Is a structural polysaccharide in plant cell
  walls.
• What enzyme would digest cellulose? (Cellulase)

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Polysaccharide structures
Amylose alpha-glycoside linkages
Cellulose beta-glycoside linkages
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Plant Starch

• Is also a homopolymer of glucose.
• Joined by a -glycoside linkages
• Is a storage polysaccharide 2 forms
              - amylose (unbranched)            
  - amylopectin (branched)
• See previous slide for amylose
• What enzyme would digest amylose? (Amylase)

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Amylopectin Structure
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Animal starch

• Glycogen animal storage polysaccharide
• Is also a homopolymer of glucose
• Joined by a-glycoside linkages
• Same as amylopectin, but more highly branched

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Structure of Glycogen
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Chitin

• Is a homopolymer of N-acetyl glycosamine
• Joined by b-glycoside linkages
• Is a structural polysaccharide found in fungal
  cell walls and in the exoskeleton of arthropods.

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Chitin
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Other Polysaccharides

• Chondroitin - Major polysaccharide of cartilage.
• Heparin - Anticoagulant prevents blood clots.
• Hyaluronic acid - "glue" between animal cells