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Biochemistry
Biochemistry is the study of chemical substances found in living systems and the chemical interactions of these substances with each other.
A biochemical substance is a chemical substance found within a living organism.
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Biochemistry
Biochemistry Biochemistry
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14.2 Intro to Carbohydrates
Carbohydrates are biomolecules that decom-pose to produce carbon and water. Their empirical formulas are approximately CH2O.
Carbohydrates are produced in plants by photosynthesis.
CO2 + H2Osunlight
chlorophyllenzymes
Carbohydrates + O2
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14.2 Intro to 14 Carbohydrates
Carbohydrates are scarce in animals, but account for ~75% of dry mass in plants.
Uses of carbohydrates:
Oxidized to provide energy
Serve as stored form of chemical energy
Supply carbon for biosynthesis in cells
Form structures of some cells and tissues
Are markers on cell surfaces
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14.3 Types of CarbohydratesCarbohydrates are polyhydroxy aldehydes,
polyhydroxy ketones, or substances that produce such compounds by hydrolysis.
C
C
OH
H OH
C HHO
C OHH
C OHH
CH2
C O
C
C
HHO
H OH
C OHH
CH2
Glucose,a polyhydroxy
aldehyde
Fructose,a polyhydroxy
ketone
OH
CH2 OH
OH
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14.3 Types of CarbohydratesCarbohydrates are classified by size. Mono-
saccharides contain one polyhydroxycarbonyl unit. Larger carbohydrates contain chains of these units, linked by covalent bonds.
monosaccharide disaccharide
oligosaccharide (3 - 10 monosaccharide units)
polysaccharides contain many(sometimes >10,000)
monosaccharide units
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14.4 Types of Monosaccharides
Monosaccharides are classified by
1. The type of carbonyl group:
Aldose or Ketose
2. The number of carbons:
Triose (3 carbons) Tetrose (4 carbons) Pentose (5 carbons) Hexose (6 carbons)
Competency XIII-1
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14.4 Types of Monosaccharides
MonosaccharidesC
C
OH
H OH
C HHO
C OHH
C OHH
C OHH
H
C
C O
OHH
H
C
C
OHH
H OH
C OHH
H
Glucose, an aldohexose Ribulose, a ketopentose
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14.5 Handedness
Shapes of molecules are incredibly important in biochemistry. Molecules that have the same formula but different shape are called isomers.
There are several types of isomers:
Constitutional Isomers
Stereoisomers Geometric Optical
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14.5 Handedness
Types of isomers:
Constitutional isomers, or structural isomers, are isomers that differ in their bonding sequence or connectivity.
C
H3C
C
CH3
H
H
C C
CH3
CH3
H
H
H2C
H2C CH2
CH2
trans-2-butene cyclobutane 2-methylpropene
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14.5 HandednessTypes of isomers:
Stereoisomers are isomers that differ only in how their atoms are oriented in space. The connectivity is the same in all the isomers. There are two types of stereoisomers.
Geometric isomers, or cis-trans isomers:
C
H3C
C
CH3
H
H
C
H
C
CH3
H
H3Ctrans-2-butenecis-2-butene
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14.5 Handedness
Types of isomers:
Optical isomers are mol-ecules that interact with polarized light.
The simplest of these are nonsuperimposable mirror images of each other. They are called enantiomers.
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14.5 Handedness
Molecules that can have enantiomers must have chiral centers.
Chiral centers are tetrahedral carbons with four different substituents. The substituents can be individual atoms or functional groups.
C
J
KC
J
KL LM M
1 2
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14.5 Handedness
Pairs of molecules with nonsuperimposable mirror images are called enantiomers.
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14.5 Handedness
Carbohydrates have many stereoiso-mers.
Glyceraldehyde, the simplest carbohy-drate, has enan-tiomers. It is an aldotriose.
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14.5 HandednessEach enantiomer in a pair has the same prop-
erties unless it interacts with another chiral substance. Biological molecules are usually chiral.
H3C
O
C
HC H
H
CH3CH3
O
C
HCH
H
CH3
(S)-(+)-Carvone
odor of caraway
(R)-(−)-Carvoneodor of spearmint
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14.5 HandednessCompounds can have more than one chiral
center. The number of stereoisomers is 2n, where n is the number of chiral centers.
C
C
OH
HO H
C HHO
C OHH
C OHH
CH2 OH
C
C
OH
H OH
C HHO
C HHO
C OHH
CH2 OH
C
C
OH
H OH
C HHO
C OHH
C OHH
CH2 OH
glucose mannose galactose
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14.5 HandednessStereoisomers of compounds with more than
one chiral center that are not enantiomers (mirror images) are called diastereomers.
A B C D
A & B, C & D, pairs of enantiomers A is a diastereomer of C & D.
C
C
A
E
D
F
H
G
C
C
A
E
D
F
H
G
C
C
E
A
D
F
H
G
C
C
E
A
D
F
H
G
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14.5 Handedness
In carbohydrates, handedness is shown in Fischer projections. The right-handed isomer is the D-(dextro) isomer; the left-handed isomer is the L-(levo) isomer.
C
C
C
OHH
OHH
H
O H
C
C
C
HO H
HOH
H
OH
D-glyceraldehydeL-glyceraldehyde
CHO
CH2OH
OHH
CHO
CH2OH
HHO
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14.5 Handedness
In carbohydrates with many chiral centers, the carbon furthest from the carbonyl group is used for this designation.
Naturally occuring car-bohydrates are all D- isomers.
COH
H OH
HHO
OHH
OHH
CH2 OH
D-glucose
CO H
HHO
H OH
HO H
HO H
CH2HO
L-glucose
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14.7 Cyclization
Monosaccharides contain carbonyl and hydroxyl groups. These react to form hemiacetals. The reactions are spon-taneous, intramolecular, and form cyclic products.
Ring size:
6 atoms pyranose
5 atoms furanose
O O
Pyran Furan
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14.7 Cyclization
Ring size:
6 atoms pyranose
5 atoms furanose
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14.7 Cyclization
Hemiacetals can form in two orientations:
36% 64%
C
C C
C
OCH
OHH
OH
OH
H
H
OH
CH2
H
OH
C
C C
C
OCOH
HH
OH
OH
H
H
OH
CH2
H
OH
α-D-glucose β-D-glucose
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14.8 RXN’s of Monosaccharides
Aldoses are easily oxidized. Benedict’s test with Cu2+ can be used to detect them.
Tollens’ test, which produces metallic silver, is also useful.
C
C
HO
H OH
R
+ Cu2+
C
C
OHO
H OH
R
Cu2O
bluesol'n
reddishsolid
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14.8 RXN’s of MonosaccharidesPositive Benedict’s test.
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14.8 RXN’s of MonosaccharidesCarbonyl groups in monosaccharides can be
reduced to hydroxyl groups. The products are sugar alcohols.
COH
H OH
HHO
OHH
OHH
CH2 OH
D-glucose
H2
catalyst
CH2
H OH
HHO
OHH
OHH
CH2 OH
D-glucitol,a.k.a. sorbitol
OH
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14.8 RXN’s of MonosaccharidesIn the presence of alcohols, monosaccharides
form cyclic acetals called glycosides.
C
C C
C
OCH
OH
OH
OH
H
H
OH
CH2
H
OH
C
C C
C
OCO
HH
OH
OH
H
H
OH
CH2
H
OH
methyl-α-D-glucoside
Glucose + CH3 OH
CH3
CH3
H3O1+ catalyst
methyl-β-D-glucoside
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14.9 DisaccharidesDisaccharides contain two monosaccharide
units. They are bonded together through acetal/glycoside linkages. One monosac-charide supplies the carbonyl in hemiacetal form; the other provides the alcohol.
R
C
OH
OH
C
R
RRH
HO
+
hemiacetal alcohol
R
C
OH
R
OC
R
RH
acetal, a.k.a. glycoside
- H2O
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14.9 DisaccharidesMaltose is composed of two glucose units
joined by an α(14) glycoside linkage.
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14.9 DisaccharidesLactose is composed of galactose and glucose
units united in a β(14) linkage.
C
C C
C
OC
HH
OH
OH
H
OH
H
CH2
H
OH
C
C C
C
OCOH
HH
OH
OH
H
CH2
H
OH
β-D-galactose unit
D-glucoseα or β
O
H
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14.9 Disaccharides
Lactose is the sugar found in milk.
Lactose intolerance occurs when a person does not produce the enzyme to hydrolyze the β(14) glycoside linkage. Infants and children have the enzyme, but many adults do not.
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14.9 Disaccharides
Sucrose contains glucose and fructose units joined in an α,β(12) linkage.
C
C C
C
OC
H
OH
OH
H
H
OH
CH2
H
OH
C C
C
O
C
CH2 OH
CH2HO
H
OH
H
H
O
H
HO
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14.10 Polysaccharides
The major polysaccharides are polymers of glucose. In cellulose, the glucose units are joined by β(14) glycoside linkages.
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14.10 Polysaccharides
Cellulose is the major structural carbohydrate in plants.
Animals lack the enzyme cellulase, which catalyzes hydrolysis of the β(14) glyco-side linkages. They (we!) cannot metabo-lize cellulose for nutrition.
Grazing animals and termites have bacteria in their guts that produce the enzyme; these animals can feed on grass and wood.
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14.10 Polysaccharides
Starches are also polymers of glucose. They are used for energy storage in plants. There are two forms, amylose and amylopectin.
Amylose is a straight-chain polymer in which glucose units are linked by α(14) glyco-side linkage.
Amylopectin is a branched-chain polymer. The branches are formed by α(16) link-ages.
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14.10 Polysaccharides
Comparison of amylose and amylopectin structures.
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14.10 Polysaccharides
Amylopectin, showing glycoside linkages.
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14.10 Polysaccharides
Glycogen, sometimes called animal starch, is structurally similar to amylopectin.
Glycogen is formed when excess glucose is present in the blood; the process is called glycogenesis. Glycogen is stored in the liver and muscle tissue.
When blood glucose is low, glycogen is hydrolyzed to release glucose. The process is called glycogenolysis.