Transcript Chem 150 Unit 9 - Biological Molecules II Carbohydrates
Chem 150 Unit 9 -
Biological
Molecules II Carbohydrates
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 sun’s 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 earth’s organic carbon than any other molecule.
2
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 .
Introduction
3 • • • 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.
O H O H H H H O C C H H O O H H H O H H O H
Monosaccharides
7 • • Monosaccharides contain
chiral carbon
atoms.
This is what accounts for the large number of different monosacchides.
For each chiral carbon,
n
, a monosacharide has 2 n • stereoisomers.
These will be divided among 2 n /2 pairs of
enantiomers
.
• Glucose contains 4 chiral carbons O H • Glucose has 2 4 = 16 stereoisomers C H C OH • These stereoisomers can be grouped into 16/2 = 8 pairs of enantiomers.
HO H C C OH OH H H C C OH OH H
D -glucose
http://www.preparatorychemistry.com/Bishop_Jmol_carbohydrates.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.
Fischer projection:
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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
and nucleotides such as FADH 2 are found in DNA, RNA 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 OH’s are replaced with -H’s
Monosaccharides
• Monosaccharide derivatives • •
Amino sugars
.
One or more OH’s are replaced with -NH 2 ’s Often these are acetylated to form amides.
13 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: A) D-2-deoxyxylose B) xylitol C) D-xylonic acids (carbon 1 is oxidized to a carboxylic acid) O C H H HO H C C C OH H OH CH 2
D -xylose
OH
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!
17 http://patft.uspto.gov/netacgi/nph Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fne tahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=5091200.
PN.&OS=PN/5091200&RS=PN/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 H 2 In the cell, NADH + H + is used.
and a platinum catalyst.
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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 H 2 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 Benedict’s 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 (Cu 2+ ) • • This reaction oxidizes aldehydes, but not alcohols.
The Cu 2+ ion forms a clear blue solution The Cu + that is produced in the reaction forms an orange/red precipitate.
Oxidation of Aldehydes (Unit 8)
24 Aldehydes can also be oxidized with the copper(II) • ion (Cu 2+ ) The reaction is called the Benedict’s reaction, and has been used for years in a clinical setting to test for the presence of C H glucose in the urine.
H C OH HO C H H H C C OH OH CH 2
glucose
OH Cu 2+ Cu 2+ + Cu + Cu +
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Reactions of Monosaccharides
• • Oxidation of sugars Even though ketones should not give a positive Benedict’s 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).
O H 3 C CH 2 C Propanal (Aldehyde) H + H O CH 2 CH 3 Ethanol (Alcohol) H 3 C O H CH 2 C H O (Hemiacetal) CH 2 CH 3 O CH 3 C CH 3 + Propanone (Ketone) H O CH 2 CH 3 Ethanol (Alcohol) O H CH 3 C CH 3 O CH 2 CH 3 (Hemiketal)
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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.
Cyclic Form of Monosaccharides
Monosaccharides form rings by reacting one of the hydroxyls with the carbonyl to form a hemiacetal or hemiketal: 30 http://www.preparatorychemistry.com/Bishop_Jmol_carbohydrates.htm
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Cyclic Form of Monosaccharides
• • • Usually these are drawn using a
Haworth project
: The OH’s that were on the
right
in the Fisher projection are placed in the
down
position on the Haworth projection The OH’s that were on the
left
in the Fisher projection are placed in the
up
position on the Haworth projection The CH 2 OH 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 α or β.
The β-anomer has the -OH pointing up in the ring form.
The α-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: D -glucose (aldohexose) • Aldopentoses and ketohexoses will form furanose rings: D -ribose (aldopentose) D -fructose (ketohexose)
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Question (Clicker)
Shown below is the Fischer projection for sorbose A) B) H L-sorbose HO C C OH H H C Draw and name the α and β CH 2 OH OH ring forms for sorbose CH 2 OH OH O H CH 3 OH H H OH OH α D -sorbofuranose CH 2 OH OH O H OH H H OH CH 2 OH β D -sorbofuranose
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Question (Clicker)
Shown to the below is the Fischer projection for galactose O H A) B) D -galactose H C H OH L -galactose HO C H CH OH Draw and name the α and β ring forms for sorbose H H O CH 2 OH H OH H OH OH OH H α L -galactopyranose H H O CH 2 OH H OH OH OH H OH H β L -galactopyranose
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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: O H + H O CH 2 CH 3 O CH 2 CH 3 H 3 C CH 2 C H O (Hemiacetal) CH 2 CH 3 Ethanol (Alcohol) H 3 C CH 2 C O H (Acetal) CH 2 CH 3 + H O H O H + H O CH 2 CH 3 CH 3 C CH 3 O CH 2 CH 3 (Hemiketal) Ethanol (Alcohol) O CH 2 CH 3 CH 3 C CH 3 O CH 2 CH 3 + H O H (Ketal)
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Oligosaccharides
The
disaccharide D -maltose
forms when the anomeric carbon on a D glucopyranose molecule in the α form reacts with the hydroxyl group on the forth carbon of a second D • glucopyranose molecule: The bond that forms is called an α(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 Benedict’s 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
Oligosaccharides
42 The
disaccharide D -cellobiose
forms when the anomeric carbon on a D glucopyranose molecule in the β form reacts with the hydroxyl group on the forth carbon of a second D • glucopyranose molecule: The bond that forms is called an β(1→4) glycosidic bond Cellobiose is produced from the breakdown of the polysaccharids cellulose.
Unlike the α(1→4) glycosidic bond in maltose, most organisms are unable to cleave the β(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 β form reacts with the hydroxyl group on the forth carbon of a D • glucopyranose molecule: The bond that forms is called an β(1→4) glycosidic bond Lactose is milk sugar.
By the age of 5, some people become unable to break the β(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 α form reacts with the hydroxyl group of the anomeric carbon of D • fructofuranose in the β form: The bond that forms is called an α,β(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
monosaccharide unit.
Heteropolysaccharides
contain a single type of 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 β(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 β(1→4) glycosidic bonds
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 α(1→4) glycosidic bonds amylose 49 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