chem 1123_unit 7a
TRANSCRIPT
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Introduction to Biochemistry
Carbohydrates
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Carbohydrates
Carbohydrates are
a major source of energyfrom our diet.
composed of the elementsC, H and O.
also called saccharides,
which means sugars.
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Carbohydrates
Carbohydrates
are produced byphotosynthesis in plants.
such as glucose aresynthesized in plantsfrom CO2, H2O, andenergy from the sun.
are oxidized in living cellsto produce CO2, H2O,and energy.
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Types of Carbohydrates
The types of carbohydrates are
monosaccharides, the simplest carbohydrates. disaccharides, which consist of two monosaccharides. polysaccharides, which contain many monosaccharides.
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Monosaccharides
Monosaccharides consist of
3-6 carbon atoms typically.
a carbonyl group (aldehyde or ketone). several hydroxyl groups. 2 types of monosaccharide structures:
Aldoses and ketoses
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Aldoses
Aldoses are monosaccharides
with an aldehyde group with many hydroxyl (-OH)
groups.triose (3C atoms)
tetrose (4C atoms)
pentose (5 C atoms)
hexose (6 C atoms)
O
CH aldose
HCOH
HCOH
CH2OH
Erythose, an aldotetrose
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Ketoses
Ketoses are monosaccharides
with a ketone group with many hydroxyl (-OH)
groups.
CH2OH
C=O ketose
HCOH
HCOH
HCOH
CH2OH
Fructose, a ketohexose
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Learning Check
Identify each as aldo- or keto- and as tetrose,pentose, or hexose:
H
CH2OH
OHC
H
H
H
OH
OH
OH
C
C
C
HC
O
CH2OH
HHO
CH2OH
O
H OHC
C
C
aldohexoseketopentose
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Structures ofMonosaccharides
Copyright 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Fischer Projections
A Fischer projection
is used to represent carbohydrates. places the most oxidized group at the top. shows chiral carbons as the intersection of vertical and
horizontal lines.
Copyright 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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D and L Notations
In a Fischer projection, the OH group on the chiral carbon farthest from the carbonyl group
determines an L or D isomer.
left is assigned the letter Lfor the L-form.
right is assigned the letter Dfor the D-form.
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Examples of D and L Isomers ofMonosaccharides
D-glucose D-ribose L-galactose
O
CH2OH
H OH
H OH
HO HOHH
C H
CH2OH
H OH
H OH
OHHHC
OH
O
CH2OH
HO H
H OH
H OH
HHO
C
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D-Glucose
D-glucose is
found in fruits, cornsyrup, and honey.
an aldohexose with
the formula C6H12O6. known as blood sugar
in the body.
the monosaccharide in
polymers of starch,cellulose, andglycogen.
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D-Fructose
D-fructose
is a ketohexoseC6H12O6.
is the sweetestcarbohydrate.
is found in fruit juicesand honey.
converts to glucose inthe body.
H OH
CH2
OH
C
HOH OH
HC
O
C
C
CH2OH
D-Fructose
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Cyclic Structures
Cyclic structures
are the prevalent form of monosaccharides with 5 or 6carbon atoms.
form when the hydroxyl group on C-5 reacts with thealdehyde group or ketone group.
O
O
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H
OHH
OH
C
H H
OH OH
C C CH
O
CHOCH2
Drawing the Cyclic Structure forGlucose
STEP 1 Number the carbon chain and turn clockwise toform a linear open chain.
HHO
H
CH2OH
OHC
H
H
OH
OH
C
C
C
OH
C1
2
3
4
5
6
6 5 4 3 2 1
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Cyclic Structure for Glucose(cont)
OH
OH
OHOH
CH2OH
O
-D-Glucose -D-Glucose
OH
OH
OH
OH
CH2OH
O
STEP 3 Write the newOH on C1 down for the form. up for the form.
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Summary of the Formation ofCyclic Glucose
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-D-Glucose and -D-Glucose inSolution
When placed in solution, cyclic structures open and close. -D-glucose converts to -D-glucose and vice versa. at any time, only a small amount of open chain forms.
-D-glucose D-glucose (open) -D-glucose
(36%) (trace) (64%)
OH
CH2OH
OH
OC
H
OH
OHOH
OH
OHOH
CH2OH
OOH
OH
OHOH
CH2OH
O
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Cyclic Structure of Fructose
Fructose is a ketohexose. forms a cyclic structure. reacts the OH on C-5 with the C=O on C-2.
D-fructose -D-fructose-D-fructose
O CH2OH
OH
OH
OH
CH2OH O OH
CH2OH
OH
OH
CH2OH
H OH
H OH
HHO
O
CH2OH
C
C
C
C
CH2OH
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Disaccharides
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Important Disaccharides
A disaccharideconsists of two monosaccharides.
Monosaccharides Disaccharide
glucose + glucose maltose + H2Oglucose + galactose lactose + H2O
glucose + fructose sucrose + H2O
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Maltose
Maltose is
a disaccharide also known as malt sugar. composed of two D-glucose molecules.
obtained from the hydrolysis of starch. used in cereals, candies, and brewing. found in both the - and - forms.
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Formation of Maltose
Free -OH
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Lactose
Lactose
is a disaccharide of -D-galactose and -or-D-glucose.
contains a -1,4-glycosidic bond.
is found in milk andmilk products.
-form-form
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Sucrose
Sucrose or table sugar is obtained from sugar cane and sugar beets. consists of -D-glucose and -D-fructose.. has an ,-1,2-glycosidic bond.
-D-glucose
-D-fructose
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Sweetness of Sweeteners
Sugars and artificialsweeteners
differ insweetness.
are compared tosucrose (tablesugar), which is
assigned a valueof 100.
60 000
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Learning Check
Identify the monosaccharides in each of the following:A. lactose
(1) -D-glucose (2) -D-fructose (3) -D-galactose
B. maltose
(1) -D-glucose (2) -D-fructose (3) -D-galactose
C. sucrose(1) -D-glucose (2) -D-fructose (3) -D-galactose
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Polysaccharides
Copyright 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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Polysaccharides
Polysaccharides
are polymers of D-glucose. include amylose and amylopectin,
starches made of
-D-glucose.
include glycogen (animal starch inmuscle), which is made of -D-glucose.
include cellulose (plants and wood),which is made of -D-glucose. -D-Glucose
O
CH2OH
OH OH
OH
OH
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Structures of Amylose andAmylopectin
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Amylose
Amyloseis
a polymer of -D-glucose molecules.
linked by -1,4glycosidic bonds.
a continuous(unbranched) chain.
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Amylopectin
Amylopectin
is a polymer of -D-glucose molecules.
is a branched-chainpolysaccharide.
has -1,4-glycosidicbonds between theglucose units.
has -1,6 bonds tobranches.
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Dextrins
Starches like amylose and amylopectinhydrolyze to dextrins (smallerpolysaccharides)
Contain 3-8 glucose units
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Glycogen
Glycogen
is the polysaccharidethat stores -D-glucose
in muscle. is similar to amylopectin,
but is more highlybranched.
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Cellulose
Cellulose
is a polysaccharideof glucose units inunbranched chains.
has -1,4-glycosidicbonds.
cannot be digestedby humans because
humans cannotbreak down -1,4-glycosidic bonds.