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Chapter 12 Carbohydrates

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Chapter 12 Carbohydrates. Carbohydrates. Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone , or a substance that gives these compounds on hydrolysis. Monosaccharide : a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate.

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Presentation Transcript
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Chapter 12

Carbohydrates

carbohydrates
Carbohydrates
  • Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis.
  • Monosaccharide:a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate.
    • Monosaccharides have the general formula CnH2nOn, where n varies from 3 to 8.
    • Aldose: a monosaccharide containing an aldehyde group.
    • Ketose: a monosaccharide containing a ketone group.
monosaccharides
Monosaccharides
  • Monosaccharides are classified by their number of carbon atoms.
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Example: aldo (from aldehyde)

pent (from 5 carbons)

ose (family name)

ALDOPENTOSE

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Example
    • keto (from ketone)
    • hex (from 6 carbons)
    • ose (family name)

KETOHEXOSE

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Chiral- compounds or objects that can not

be superimposed on their mirror image.

Object is different from its mirror image

  • Achiral (nonchiral)- compounds or objects that can be superimposed on their mirror image.

Object is the same as its mirror image

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A chiral carbon is one that has four different groups attached to it.

  • A carbon with four different groups bonded to it is called a stereocenter.
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Enantiomers- Isomers where the

    • molecule and its mirror image are different.
    • They always occur in pairs
two stereocenters
Two Stereocenters
  • For a molecule with nstereocenters, the maximum number of possible stereoisomers is 2n.
    • We have already verified that, for a molecule with one stereocenter, 21 = 2 stereoisomers (one pair of enantiomers) are possible.
    • For a molecule with two stereocenters, a maximum of 22 = 4 stereoisomers (two pair of enantiomers) are possible.
    • For a molecule with three stereocenters, a maximum of 23 = 8 stereoisomers (four pairs of enantiomers) are possible.
stereoisomers
Stereoisomers
  • example: Mark all stereocenters in each molecule and tell how many stereoisomers are possible for each.
chirality in biomolecules
Chirality in Biomolecules
  • how an enzyme distinguishes between a molecule and its enantiomer.
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The S enantiomer of naproxen is the active pain reliever, but its Renantiomer is a liver toxin!
monosaccharides1
Monosaccharides
  • Fischer projection:a two dimensional representation for showing the configuration of tetrahedral stereocenters.
    • Horizontal lines represent bonds projecting forward from the stereocenter.
    • Vertical lines represent bonds projecting to the rear.
    • Only the stereocenter is in the plane.
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Haworth Projections

Monosaccharides with 5 or more carbons exist as rings

Haworth projection

ALDOSE

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Haworth projection

Fischer projection

KETOSE

important monosaccharides
Important Monosaccharides
  • Glucose
  • Aldohexose
  • Most nutritionally important monosaccharide
  • Sometimes called dextrose or blood sugar
galactose
Galactose
  • A component of lactose (milk sugar)
  • Aldohexose
fructose
Fructose
  • Ketohexose
  • Sometimes called fruit sugar
  • Component of sucrose
disaccharides
Disaccharides
  • Two monosaccharide units linked together

Glycosidic

Linkage (1→4)

Glucose

Glucose

Maltose

important disaccharides
Important Disaccharides
  • Maltose
  • Glucose + Glucose
  • Malt sugar
  • Found in fermenting grains
lactose
Lactose
  • Glucose + Galactose
  • Milk sugar
lactose intolerance
Lactose Intolerance
  • Enzyme Lactase low or absent
  • Lactose fermented in the intestine
  • Nausea, cramps, bloating, gas, and diarrhea
sucrose
Sucrose
  • Fructose + Glucose (1→2)
  • Found in many plants (especially sugar cane, sugar beets)
  • Table sugar

glucose

fructose

polysaccharides
Polysaccharides
  • More than 10 monosaccharides linked together

Glycosidic

linkage

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Starch
  • Polymer of 30 to 1000 glucose units
  • Storage form of glucose in plants
  • Cereal grains (wheat, rice, corn, oats, barley) as well as tubers such as potatoes are rich in starch
glycogen
Glycogen
  • Polymer of glucose units
  • Storage form of glucose in animals
  • Can have up to 600,000 glucose units
  • Mainly in liver and muscles
    • (1→4 and 1→6 links)
cellulose
Cellulose
  • Polymer of glucose units
  • Found in plant cell walls
  • Linear polymer but has  (14)glycosidic linkages.
  • Not easily digested, a constituent of dietary fiber.
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