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Introductory Chemistry:
A Foundation
FIFTH EDITION
by Steven S. Zumdahl
University of Illinois
Copyright©2004 by Houghton
Mifflin Company. All rights reserved.
1
Biochemistry
Chapter 20
Copyright©2004 by Houghton
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2
Biochemistry
• Biochemistry is the chemistry of living
things
– Look at living things on a molecular level
• 30 essential elements
– Macronutrients = H, C, N, O, S, Na, Mg, P, Ca,
K, Cl
– Trace elements = first transition row elements
• Many required for enzyme function
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3
Proteins
• Natural polymers that make up 15% of
body weight
• Fibrous Proteins provide structural
integrity and strength to tissues
• Globular Proteins transport O2 and
nutrients through body, act as catalysts,
fight disease, participate in metabolism
and cell regulation
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4
Protein Primary Structure
• Protein polymer made of chain of -amino
acids
• Amino acids contain both a carboxylic acid
functional group (-COOH) and an amine
functional group (-NH2)
• The  indicates that both functional groups
are attached to the same carbon
R1 O
H2N
C
C
OH
H
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5
Amino Acid R Groups
• R groups also called side chains
• Classified as either polar or non-polar
– Non-polar contain mostly C & H
– Polar contain O & N
• Polar side chains are hydrophilic, Nonpolar side chains are hydrophobic
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6
Linking Amino Acids
• The OH of the acid group on one amino
acid combines with a H on the amine group
of another amino acid, releasing water and
joining the C of the acid group to the N
R1 O
H 2N
C
H
C
R1 O
R1 O
OH
+HN
2
C
H
C
OH
H 2N
C
H
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C
R1 O
N
H
C
C
OH
+
H
7
H2O
Primary Structure of Proteins
•
•
•
•
Bond between amino acids is called a peptide bond
Dipeptide = 2 amino acids
Polypeptide = many amino acids
The sequence of amino acids is called the primary
structure of the protein
• Use shorthand 3-letter abbreviations of amino acids
• Primary structure indicated by amino acid
abbreviations attached together
• Polypeptides that contain the same amino acids, but
different primary structures, can have vastly different
properties and biological effects
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8
Secondary Structure of Proteins
• Secondary Structure is the arrangement of the
polymer chain in space
• It is determined by intramolecular attractive forces
– Mainly H-bonds
• The -helix is a spiral structure
– Gives fibrous proteins their spring
• The pleated sheet involves several peptide chains
aligned in rows forming a corrugated sheet
– Give fibrous proteins their flexibility and resistance to stretch
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9
Tertiary Structure of Proteins
• Tertiary Structure is the overall shape of
the protein
– Determines whether the protein will be long
and narrow fibers or spherical globules
• Much of the tertiary structure is stabilized
by S-S bonds that form between cysteine
amino acids in the same chain or between
chains
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10
Disulfide Linkages
• The -SH side chains on 2 cysteine amino
acids can join together to form a –S-S- bond
• This is called a disulfide linkage
– a.k.a. disulfide bridge
• Disulfide linkages cause bends in the
protein chain or attach chains together
• The –S-S- bond is not very strong, easily
broken
• Results in breakdown of tertiary structure
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11
Structure and Function of Proteins
• 3-dimensional structure vital to the function
of the protein
• Breaking down the 3-dimensional structure
is called denaturation
• Denaturation can be caused by the addition
of energy or a chemical reaction
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12
Enzymes
• Enzymes are proteins that catalyze specific biological
reactions.
– Most biological reactions would be too slow for living systems
– As catalysts, enzymes are not consumed in the reaction
• The lock-and-key model of enzyme activity says that
enzymes function by binding to the reacting molecule
– The reacting molecule(s) is called the substrate
• In order for the reaction to take place, the substrate must
bind to the enzyme by fitting into a specific part of the
enzyme called the active site
• After reaction has taken place, the products no longer fit
well into the active site and are released from the enzyme
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13
Carbohydrates
•
•
•
•
•
Contain Carbon, Hydrogen & Oxygen
Contain carbonyl groups and alcohol groups
Also known as sugars, starches, cellulose, dextrins & gums
Hydroxycarbonyls - have many OH & one C=O
Monosaccharides - cannot be broken down into simpler
carbohydrates
• Disaccharides - two monosaccharides linked
– Loose H from one and OH from other
• Polysaccharides - 3 or more monosaccharides linked into
complex chains
– Starch and cellulose polysaccharides of glucose
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14
Cyclic Monosaccharides
• Oxygen attached to second last carbon bonds to
carbonyl carbon
• Convert carbonyl to OH
– Transfer H from original O to carbonyl O
• New OH group may be same side as CH2OH ()
or opposite side ()
CH2OH
O
H
HO
HO H HO H
OH
H
HO
H
H
H
O
Glucose
CH2 OH
H
HO H
H OH
OH
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15
Glucose Polysaccharides
• Made of glucose rings linked together
– Give only glucose on hydrolysis
– Differ in the manner rings linked together
• Starch digestible by humans, Cellulose not
– The enzymes in humans can only work on the glycosidic linkage found in
starch
•
•
•
•
Starch is the carbohydrate storage reservoir in plants
Cellulose is the major woody structural component of plants
Glycogen is the main carbohydrate storage reservoir in animals
Hydrolysis breaks poly and disaccharides into monosaccharides by
adding water to break the molecules down
– Under acidic or basic conditions
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16
Nucleic Acids
•
•
•
•
carry genetic information
DNA molar mass up to several billion grams
RNA molar mass up to 40,000 grams
made of nucleotides
– Phosphate group
– 5 carbon sugar
– cyclic amine (nitrogen containing organic base)
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17
DNA
RNA
• deoxyribonucleic acid
• sugar is deoxyribose
• one of the following
amine bases
– adenine (A)
– guanine (G)
– cytosine (C)
– thymine (T)
• 2 DNA strands wound
together in double
helix
• ribonucleic acid
• sugar is ribose
• one of the following
amine bases
 adenine (A)
 guanine (G)
 cytosine (C)
 uracil (U)
• single strands wound
in helix
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18
Nucleotide Formation
+
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19
Base Pairing
• base pairing generates the helical structure
• A with T or U, C with G
• in DNA, the two strands have complimentary
bases
– hold strands together
– allow replication of strand
Thymine
Adenine
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20
DNA and Protein Synthesis
• Besides replication, the major function of DNA is to
provide the blueprint for the amino acid sequence of
proteins
• Genes are specific segments of the DNA strand that
code for a particular protein
• First the code is transferred to messenger RNA
– transcription
• Then transfer RNA carries amino acids to the mRNA
where they are matched up and joined together
– translation
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21
Fats & Oils: Triglycerides
• Fats are solid at room temperature, oils are
liquids
• Triesters of glycerol with fatty acids
• Triglycerides differ in
– Length of the fatty acid side-chains (12 to 20 C)
– Number of C=C in side-chain
• Degree of unsaturation
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22
Structure and Melting Point
• Larger fatty acid = Higher
melting point
• Double bonds decrease the
melting point
• Saturated = no DB
• Monounsaturated = 1 DB
• Polyunsaturated = many DB
Name
Myristic Acid
MP
Class
°C
58 Sat., 14 C
Palmitic Acid
63 Sat, 16 C
Stearic Acid
71 Sat, 18 C
Oleic Acid
16 1 DB, 18 C
Linoleic Acid
-5 2 DB, 18 C
Linolenic Acid -11 3 DB, 18 C
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23
Soaps
• Triglycerides can be broken down into fatty acids salts and
glycerol by treatment with a strong hydroxide solution
• The reaction is called saponifcation
• Fatty acid salts have a very polar “head” because it is ionic
– Hydrophilic
• Fatty acid salts also have a very non-polar “tail” because it is all
C and H
– Hydrophobic
• This unique structure allows the fatty acid salts, called soaps, to
help oily substances be attracted to water through micelle
formation
– Surfactants or wetting agents
– Ca+2 and Mg+2 precipitate soaps = soap scum
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24
Phospholipids
• Esters of glycerol
• Glycerol attached to 2 fatty acids and 1 phosphate group
• Phospholipids have polar head due to phosphate group as
well as non-polar tail from the fatty acids
Waxes
• Waxes are esters of fatty acids and long chain alcohols
• Solids
• Furnish waterproof coatings
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25
Steroids
• Characterized by 4 linked carbon rings
• Mostly hydrocarbon-like
– Dissolve in animal fat
• Mostly have hormonal effects
• Serum cholesterol levels linked to heart disease and stroke
– Levels depend on diet, exercise, emotional stress, genetics, etc.
– Trans double bonds from partially hydrogenated oils increase
• Cholesterol synthesized in the liver from saturated fats
CH2
CH3
H2C
H2C
HO
C
H
CH2
CH2
CH3
CH
CH2
CH
CH3
C
C
C
CH H
C
CH2
CH
CH
CH2
CH2
CH
CH3
CH3
CH2
CH2
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26