Chem 150 Unit 9 Biological Molecules II Carbohydrates

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Chem 150Unit 9 - Biological Molecules
IICarbohydrates

• Carbohydrates play many important roles in
  biological systems. They represent the major form
  of chemical energy for both plants and animals.
  In plants they represent the end product of
  photosynthesis, and therefore connect all living
  systems to the suns sustaining light energy. Our
  discussion of carbohydrates will also introduce
  us to biopolymers, of which proteins and nucleic
  acids also belong. One of these polymers, the
  structural polysaccharide cellulose, ties more of
  the earths organic carbon than any other
  molecule.

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Introduction

• Polymers are large molecules that are made by
  stringing together, like beads on a string,
  smaller units called monomers.
• Poly- is the Greek prefix meaning many.
• The names of may polymers describe what they are
  made from
• Polyethylene is made by stringing together many
  ethylene units.
• Ethylene (ethene) is the monomer
• Polypropylene is made by stringing together many
  propylene units.
• Propylene (propene) is the monomer.
• Polysaccharides are made by stringing together
  many monosaccharides.
• Monosaccharides (simple sugars) are the monomers.

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Introduction

• Carbohydrates are placed in to one of three
  catagories, depending on the number of
  monosaccharide units, or residues, they contain.
• Monosaccharides, contain a single monosaccharide
  residue.
• Oligosaccharides, contain 2 to 10 monosaccharide
  residues.
• These include the disaccharides, which contain 2
  monosaccharide residues.
• Polysaccharides, which contain more than 10
  monosaccharide residues.
• These can contain thousands of monosaccharide
  residues.

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Monosaccharides

• Monosaccharides are polyhydroxy aldehydes or
  ketones.
• Monosaccharides contain 3 to 7 carbon atoms.

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Monosaccharides

• Monosaccharides are classified according to the
  number of carbons and whether they contain an
  aldehyde or ketone.
• The -ose ending is used to designate
  carbohydrates.

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Monosaccharides

• The physical properties of monosaccharides are
  heavily influenced by the large number of hydroxy
  groups that they contain.
• There ability to participate in numerous hydrogen
  bonds gives them high melting points and high
  solubilities in water.
• Each hydroxyl group has two hydrogen bonding
  acceptor sites and one hydogen bonding donor
  site.
• Each carbonyl group has two acceptor sites.

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Monosaccharides

• Monosaccharides contain chiral carbon atoms.
• This is what accounts for the large number of
  different monosacchides.
• For each chiral carbon, n, a monosacharide has 2n
  stereoisomers.
• These will be divided among 2n/2 pairs of
  enantiomers.

• Glucose contains 4 chiral carbons
• Glucose has 24 16 stereoisomers
• These stereoisomers can be grouped into 16/2 8
  pairs of enantiomers.

http//www.preparatorychemistry.com/Bishop_Jmol_ca
rbohydrates.htm
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Monosaccharides

• Fischer projections are used to distinguish the
  different stereoisomers.
• The letters D and L are used to distinguish
  between the members of a pair of enantiomers.
• The D or L designation is based on the chiral
  carbon furthest from the carbonyl carbon.

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Monosaccharides

• Diasteriomers are stereoisomers that are not
  enantiomers.
• Diasteriomers have have different names
• Enatiomers have the same name and are
  distinguished by a D or L.

enantiomers
diastereomers
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Monosaccharides

• Important monosaccharides.
• pentose and hexoses are the most abundant
• Pentoses
• D-ribose and D-2-deoxyribose are found in DNA,
  RNA and nucleotides such as FADH2 and NADH

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Monosaccharides

• Important monosaccharides.
• pentose and hexoses are the most abundant
• Hexoses
• D-glucose (dextrose or blood surgar) - major
  metabolite and strorage form of chemical energy.
• D-galactose - combines with glucose to produce
  lactose (milk sugar)
• D-fructose (fruit sugar) - major metabolite and
  sweetest tasting natural sugar.
• fructose is a ketose

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Monosaccharides

• Monosaccharide derivatives
• Deoxy sugars.
• One or more -OHs are replaced with -Hs

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Monosaccharides

• Monosaccharide derivatives
• Amino sugars.
• One or more -OHs are replaced with -NH2s
• Often these are acetylated to form amides.

Arthritis relief??
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Monosaccharides

• Monosaccharide derivatives
• Alcohol sugars.
• The ketone or aldehyde is reduced to an alcohol
  are reduced to

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Monosaccharides

• Monosaccharide derivatives
• Carboxylic acid sugars.
• The ketone, aldehyde, or primary alcohol is
  oxidized to a carboxylic acid.

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Question

• The monosaccharide D-xylose is shown below. Draw
  the derivative described
• D-2-deoxyxylose
• xylitol
• D-xylonic acids (carbon 1 is oxidized to a
  carboxylic acid)

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Carbo Reactions in Foods!!

• Amino acids (some) carbohydrates Browning
  flavor-
• The Maillard reaction. Also occurs in you!
• http//www.food-info.net/uk/colour/maillard.htm

Try a little corn syrup, honey, baking soda to
enhance browning!
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O1Sect2HITOFFdPALLp1u2Fnetahtml2FPTO2Fs
rchnum.htmr1fGl50s15091200.PN.OSPN/50912
00RSPN/5091200
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Carbo Reactions in Foods!!
But beware acrylamide in fries??!!
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Reactions of Monosaccharides

• Reduction of the carbonyl
• In the lab this can be done with H2 and a
  platinum catalyst.
• In the cell, NADH H is used.

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Reduction of Aldehydes and Ketones (Unit 8)

• The same reaction can also be used to reduce
  aldehydes and ketones to alcohols

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Reduction of Aldehydes and Ketones (Unit 8)

• In biochemistry, NADH H is used instead of H2
• The reduction of a ketone containing steroid by
  the enzyme Hydroxsteroid dehydrogenase.

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Reactions of Monosaccharides

• Oxidation of sugars
• Oxidation with Cu The Benedicts test
• Sugars that are capable of producing a positve
  Benedicts test are called reducing sugars.

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Oxidation of Aldehydes (Unit 8)

• Aldehydes can also be oxidized with the
  copper(II) ion (Cu2)
• This reaction oxidizes aldehydes, but not
  alcohols.
• The Cu2 ion forms a clear blue solution
• The Cu that is produced in the reaction forms an
  orange/red precipitate.

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Oxidation of Aldehydes (Unit 8)

• Aldehydes can also be oxidized with the
  copper(II) ion (Cu2)
• The reaction is called the Benedicts reaction,
  and has been used for years in a clinical setting
  to test for the presence of glucose in the urine.

Cu2
Cu
Cu2 Cu
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Reactions of Monosaccharides

• Oxidation of sugars
• Even though ketones should not give a positive
  Benedicts test, ketoses do.
• This is because under the basic conditions of the
  test, the ketoses can isomerize to form aldoses,
  which the react.

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Reactions of Monosaccharides

• Reactions with alcohols to form hemiacetals and
  hemiketals
• Since monosaccharides contain both hydroxyl
  groups along with either aldehyde or ketone
  groups, they can react to form hemiacetals and
  hemiketals.

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Reactions of Alcohols with Aldehydes and Ketones
(Unit 7)

• The first reaction, which is similar to the
  reduction of aldehydes and ketones, involves
  adding an alcohol across the carbonyl to form a
  hemiacetal (from aldehydes) or a hemiketal (from
  ketones).

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Reactions of Alcohols with Aldehydes and Ketones
(Unit 7)

• Hemiacetal and hemiketal formation is catalyzed
  by acids.

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Reactions of Alcohols with Aldehydes and Ketones
(Unit 7)

• As we will see with the carbohydrates, the
  carbonyl group and the alchohol that react can
  come from the same molecule.
• This will produce a ring molecule.

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Cyclic Form of Monosaccharides

• Monosaccharides form rings by reacting one of the
  hydroxyls with the carbonyl to form a hemiacetal
  or hemiketal

http//www.preparatorychemistry.com/Bishop_Jmol_ca
rbohydrates.htm
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Cyclic Form of Monosaccharides

• Usually these are drawn using a Haworth project
• The OHs that were on the right in the Fisher
  projection are placed in the down position on the
  Haworth projection
• The OHs that were on the left in the Fisher
  projection are placed in the up position on the
  Haworth projection
• The CH2OH on the number 5 carbon points up for D
  sugars and down for L sugars.

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Cyclic Form of Monosaccharides

• The hemiacetal or hemiketal carbon that forms in
  the ring is called the anomeric carbon.
• The anomeric carbon is also chiral, which
  increases the number of chiral carbons by 1 and
  increases the doubles the number of
  stereoisomers.
• The two forms of the anomeric carbon are
  designated as a or ß.
• The ß-anomer has the -OH pointing up in the ring
  form.
• The a-anomer has the -OH pointing down in the
  ring form.

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Cyclic Form of Monosaccharides

• The ring formation is a dynamic equilibrium
  reaction.
• The open form can switch back and forth between
  the two ring forms.

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Cyclic Form of Monosaccharides

• When naming the ring forms of monosaccharides,
  the endings -pyranose and -furanose to designate
  the six-member and five-member rings,
  respectively.

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Cyclic Form of Monosaccharides

• In general, the -OH on the chiral carbon furthest
  from the the carbonyl is the one that reacts to
  from the pyranose or furanose ring. This means
  that
• Aldohexoses will form pyranose rings
• Aldopentoses and ketohexoses will form furanose
  rings

D-glucose(aldohexose)
D-ribose(aldopentose)
D-fructose(ketohexose)
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Question (Clicker)

• Shown below is the Fischer projection for sorbose
• Is the structure shown
• D-sorbose
• L-sorbose
• Draw and name the a and ß ring forms for sorbose

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Question (Clicker)

• Shown to the below is the Fischer projection for
  galactose
• Is the structure shown
• D-galactose
• L-galactose
• Draw and name the a and ß ring forms for sorbose

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Oligosaccharides

• Monosaccharides are connected to one another to
  form oligosaccharides and polysaccharides by
  reacting the anomeric (hemiacetal or hemiketal)
  hydroxyl group on one sugar in its ring form,
  with a hydroxyl group from another sugar.
• We saw in Unit 8 how this leads to the formation
  of acetals and ketals.
• The bond that forms between the two
  monosaccharides is called a glycosidic bond.

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Reactions of Alcohols with Aldehydes and Ketones
(Unit 7)

• A hemiacetal or hemiketal can react with a second
  alcohol to form an acetal or ketal.
• This is a substitution reaction and produces an
  water molecule

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Oligosaccharides

• The disaccharide D-maltose forms when the
  anomeric carbon on a D-glucopyranose molecule in
  the a form reacts with the hydroxyl group on the
  forth carbon of a second D-glucopyranose
  molecule
• The bond that forms is called an a(1?4)
  glycosidic bond

Maltose is produced from the breakdown of the
polysaccharides starch and glycogen
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Oligosaccharides

• Maltose is still able to reduce Cu in a
  Benedicts test, though it is only 1/2 as
  reactive.
• Like monosaccharides, maltose is considered a
  reducing sugar.
• This is because the one monosaccharide is still
  able to open to expose an aldehyde.

nonreducing end
reducing end
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Oligosaccharides

• The disaccharide D-cellobiose forms when the
  anomeric carbon on a D-glucopyranose molecule in
  the ß form reacts with the hydroxyl group on the
  forth carbon of a second D-glucopyranose
  molecule
• The bond that forms is called an ß(1?4)
  glycosidic bond

Cellobiose is produced from the breakdown of the
polysaccharids cellulose. Unlike the a(1?4)
glycosidic bond in maltose, most organisms are
unable to cleave the ß(1?4) glycosidic bond
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Oligosaccharides

• The disaccharide D-lactose forms when the
  anomeric carbon on a D-galactopyranose molecule
  in the ß form reacts with the hydroxyl group on
  the forth carbon of a D-glucopyranose molecule
• The bond that forms is called an ß(1?4)
  glycosidic bond

Lactose is milk sugar. By the age of 5, some
people become unable to break the ß(1?4)
glycosidic bond in lactose, resulting in lactose
intolerance.
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Oligosaccharides

• The disaccharide D-sucrose forms when the
  anomeric carbon on a D-glucopyranose molecule in
  the a form reacts with the hydroxyl group of the
  anomeric carbon of D-fructofuranose in the ß
  form
• The bond that forms is called an a,ß(1?2)
  glycosidic bond

Sucrose is table sugar. Because both anomeric
carbons are involved in forming the glycosidic
bond, sucrose is not a reducing sugar.
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Oligosaccharides

• There are also oligosaccharides with 3 or more
  monosaccharides
• The blood group antigens are oligosaccharides
  that are attached to lipids and proteins found on
  cell surfaces.

A N-Acetyl-D-galactosamine(as shown) B
D-galactose O none
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Polysaccharides

• Polysaccharides are polymers of 10 or more
  monosaccharide units
• Homopolysaccharides contain a single type of
  monosaccharide unit.
• Heteropolysaccharides contain more than one typee
  of monosaccharide unit.

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Polysaccharides

• The polysaccharide cellulose is a structural
  polymer produced by plants
• It is a linear, unbranched polyer, with
  D-glucopyranose units connected by ß(1?4)
  glycosidic bonds

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Polysaccharides

• The polysaccharide cellulose is a structural
  polymer produced by plants
• Cellulose forms a very insoluble, fibrous network
• Most organism are unable to digest cellulose
  because they lac the enzymes needed to break the
  ß(1?4) glycosidic bonds

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Polysaccharides

• The polysaccharide starch is a polymer produced
  by plants for glucose storage
• It is a linear, or branched polymer, with
  D-glucopyranose units connected by a(1?4)
  glycosidic bonds

amylose
amylopectin
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Polysaccharides

• The polysaccharide starch is a polymer produced
  by plants for glucose storage
• Unlike cellulose, starch has a very open and
  soluble structure.
• Animals also produce a storage form of glucose
  called glycogen, which has a structure similar to
  amylopectin.

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Polysaccharides

• Heteropolymers
• Hyaluronic acid
• Found in lubricating fluid that surrounds joints
  and in the vitreous humor of the eye.

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Polysaccharides

• Heteropolymers
• Chondroitin Sulfate
• Present in connective tissue

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The End