Download Introductory Chemistry: A Foundation SIXTH EDITION

Introductory Chemistry:
A Foundation, 6th Ed.
Introductory Chemistry,
6th Ed.
Basic Chemistry, 6th Ed.
by Steven S. Zumdahl &
Donald J. DeCoste
University of Illinois
Chapter 21
Biochemistry
Biochemistry
• Biochemistry: the chemistry of living things, studied
on a molecular level
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21 | 3
Essential Elements
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21 | 4
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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21 | 5
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
H 2N
C
C
OH
H
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21 | 6
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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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
+H N
2
C
C
OH
H
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H 2N
C
H
C
R1 O
N
H
C
C
OH
+
H2 O
H
21 | 8
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.
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21 | 9
Primary Structure of Proteins (cont.)
• 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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21 | 10
Secondary Structure of Proteins
• Secondary structure: the arrangement of the
polymer chain in space
• It is determined by intramolecular attractive
forces.
– Mainly H-bonds
• The -helix is a spiral structure that gives
fibrous proteins their spring.
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21 | 11
Secondary Structure of Proteins (cont.)
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21 | 12
Secondary Structure of Proteins (cont.)
• The pleated sheet involves several peptide
chains aligned in rows forming a
corrugated sheet.
– Gives fibrous proteins their flexibility and
resistance to stretch
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21 | 13
Secondary Structure of Proteins (cont.)
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21 | 14
Tertiary Structure of Proteins
• Tertiary structure:
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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21 | 15
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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21 | 16
Structure and Function of Proteins
• 3-dimensional
structure vital to the
function of the protein
• Denaturation:
breakdown of the 3dimensional structure
• Denaturation can be
caused by the addition
of energy or a
chemical reaction
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21 | 17
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
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21 | 18
Enzymes (cont.)
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21 | 19
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
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21 | 20
Carbohydrates (cont.)
• Monosaccharides: cannot be broken down into
simpler carbohydrates
• Disaccharides: two monosaccharides linked
• Lose H from one and OH from other
(dehydration)
• Polysaccharides: 3 or more monosaccharides
linked into complex chains
• Starch and cellulose are polysaccharides of
glucose
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21 | 21
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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21 | 22
Glucose Polysaccharides
• Made of glucose rings linked together
– Give only glucose in 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
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21 | 23
Glucose Polysaccharides (cont.)
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21 | 24
Disaccharides and Polysaccharides
• 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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21 | 25
Disaccharides and
Polysaccharides (cont.)
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21 | 26
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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21 | 27
DNA
• 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
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21 | 28
RNA
• 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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21 | 29
Nucleotide Formation
O
HOH2C
OH
H
H
H
H
OH
H
N
+
O
HOH2C
N
H
N
N
H
OH
N
N
H
H
NH 2
H
N
N
HO
P
OH
O
HOH 2C
O
OH
+
N
H
H
H
H
OH
NH 2
N
N
H
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H2O
NH 2
H
NH 2
N
+
N
O
HO
P
OH
O
H2
C
O
H
N
N
N
H
+
H2 O
H
H
OH
H
21 | 30
Base Pairing
• Base pairing generates
the helical structure.
• A with T or U, C with
G
• In DNA, the two
strands have
complementary bases.
– Hold strands together
– Allow replication of
strand
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21 | 31
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
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21 | 32
DNA and Protein Synthesis (cont.)
• 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 | 33
Protein Synthesis
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21 | 34
Fats & Oils: Triglycerides
• Fats are solid at room temperature, oils are
liquids
• Triesters of glycerol with fatty acids
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21 | 35
Fats & Oils: Triglycerides (cont.)
• Triglycerides differ in
1. Length of the fatty acid side-chains (12 to 20
C)
2. Number of C=C in side-chain
3. Degree of unsaturation
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21 | 36
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
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21 | 37
Structure and Melting Point (cont.)
Myristic Acid
Class
MP
°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
Name
Linolenic Acid -11 3 DB, 18 C
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21 | 38
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
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21 | 39
Soaps (cont.)
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21 | 40
Phospholipids
• Esters of glycerol
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21 | 41
Waxes
• Waxes are esters of fatty acids and long
chain alcohols.
• Solids
• Furnish waterproof coatings
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21 | 42
Steroids
• Characterized by 4 linked carbon rings
• Four groups
1. Cholesterol
2. Adrenocorticoid hormones
3. Sex hormones
4. Bile acids
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21 | 43
Steroids (cont.)
• Serum cholesterol levels linked to heart
disease and stroke
– Levels depend on diet, exercise, emotional
stress, genetics, etc.
– Cholesterol synthesized in the liver from
CH2
saturated fats
CH2
CH
CH
3
H2C
H2C
HO
C
H
CH2
CH3
CH
C
C
CH2
CH
CH2
CH
CH3
C
C
CH H
CH
CH2
CH
3
CH3
CH2
CH2
CH2
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21 | 44