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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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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.


Example: aldo (from aldehyde)

pent (from 5 carbons)

ose (family name)

ALDOPENTOSE


  • Example

    • keto (from ketone)

    • hex (from 6 carbons)

    • ose (family name)

KETOHEXOSE



  • 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



  • A carbon with four different groups bonded to it is called a stereocenter.


Examples
EXAMPLES attached to it.


  • Enantiomers attached to it.- Isomers where the

    • molecule and its mirror image are different.

    • They always occur in pairs


Two stereocenters
Two Stereocenters attached to it.

  • 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 attached to it.

  • example: Mark all stereocenters in each molecule and tell how many stereoisomers are possible for each.


Chirality in biomolecules
Chirality in Biomolecules attached to it.

  • how an enzyme distinguishes between a molecule and its enantiomer.


  • The attached to it.S enantiomer of naproxen is the active pain reliever, but its Renantiomer is a liver toxin!


Carvone attached to it.

*

*


Thalidomide attached to it.

*

*


Fructose attached to it.


Monosaccharides1
Monosaccharides attached to it.

  • 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.


Fischer projections
Fischer Projections attached to it.



Haworth Projections attached to it.

Monosaccharides with 5 or more carbons exist as rings

Haworth projection

ALDOSE


attached to it.

Haworth projection

Fischer projection

KETOSE


Important monosaccharides
Important attached to it.Monosaccharides

  • Glucose

  • Aldohexose

  • Most nutritionally important monosaccharide

  • Sometimes called dextrose or blood sugar


Galactose
Galactose attached to it.

  • A component of lactose (milk sugar)

  • Aldohexose


Fructose
Fructose attached to it.

  • Ketohexose

  • Sometimes called fruit sugar

  • Component of sucrose


Disaccharides
Disaccharides attached to it.

  • Two monosaccharide units linked together

Glycosidic

Linkage (1→4)

Glucose

Glucose

Maltose


Important disaccharides
Important Disaccharides attached to it.

  • Maltose

  • Glucose + Glucose

  • Malt sugar

  • Found in fermenting grains


Lactose
Lactose attached to it.

  • Glucose + Galactose

  • Milk sugar


Lactose intolerance
Lactose Intolerance attached to it.

  • Enzyme Lactase low or absent

  • Lactose fermented in the intestine

  • Nausea, cramps, bloating, gas, and diarrhea


Sucrose
Sucrose attached to it.

  • Fructose + Glucose (1→2)

  • Found in many plants (especially sugar cane, sugar beets)

  • Table sugar

glucose

fructose


Polysaccharides
Polysaccharides attached to it.

  • More than 10 monosaccharides linked together

Glycosidic

linkage


  • Starch attached to it.

  • 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 attached to it.

  • 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 attached to it.

  • 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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