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Chapter 2
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The Chemistry of Life
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Introduction
• A little knowledge of chemistry can help you
choose a healthy diet, use medications more
wisely, avoid worthless health fads and frauds,
and explain treatments and procedures to your
patients or clients.
2-2
The Chemical Elements
• Element—simplest form of matter to have unique
chemical properties
• Atomic number of an element—number of protons
in its nucleus
– Periodic table
• Elements arranged by atomic number
• Elements represented by one- or two-letter symbols
– 24 elements have biological role
• 6 elements = 98.5% of body weight
– Oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus
• Trace elements in minute amounts, but play vital roles
2-3
The Chemical Elements
2-4
The Chemical Elements
• Minerals—inorganic elements extracted from
soil by plants and passed up the food chain to
humans
– Ca, P, Cl, Mg, K, Na, Fe, Zn, and S
• Constitute about 4% of body weight
– Structure (teeth, bones, etc.)
– Enzymes
• Electrolytes needed for nerve and muscle
function are mineral salts
2-5
Bohr Planetary Models of Elements
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First
energy
level
Nitrogen (N) 7p+, 7e-, 7n0
Atomic number = 7
Atomic mass = 14
Second
energy
level
Nitrogen (N) 7p+, 7e-, 7n0
Atomic number = 7
Atomic mass = 14
Third
energy
level
Sodium (Na) 11p+, 11e-, 12n0
Atomic number = 11
Atomic mass = 23
Fourth
energy
level
Potassium (K) 19p+, 19e-, 20n0
Atomic number = 19
Atomic mass = 39
Figure 2.1
p+ represents protons, n0 represents neutrons
2-6
Isotopes and Radioactivity
• Isotopes—varieties of an element that differ from
one another only in the number of neutrons and
therefore in atomic mass
– Extra neutrons increase atomic weight
– Isotopes of an element are chemically similar
• Have same valence electrons
• Atomic weight (relative atomic mass) of an
element accounts for the fact that an element is a
mixture of isotopes
2-7
Isotopes and Radioactivity
• Radioisotopes
– Unstable isotopes that give off radiation
– Every element has at least one radioisotope
• Radioactivity
– Radioisotopes decay to stable isotopes releasing
radiation
– We are all mildly radioactive
2-8
Radiation and Madame Curie
• First woman to receive
Nobel Prize (1903)
• First woman in world
to receive a Ph.D.
– Coined term radioactivity
– Discovered radioactivity of
polonium and radium
– Trained physicians in use of
X-rays and pioneered
radiation therapy as cancer
treatment
• Died of radiation
poisoning at 67
Figure 2.3
2-9
Isotopes and Radioactivity
•  particle (dangerous if inside the body)
– 2 protons + 2 neutrons; cannot penetrate skin
•  particle (dangerous if inside the body)
– free electron; penetrates skin a few millimeters
•  particle (emitted from uranium and plutonium)
– penetrating; very dangerous gamma rays
2-10
Isotopes and Radioactivity
• Physical half-life of radioisotopes
– Time needed for 50% to decay into a stable state
– Nuclear power plants create radioisotopes
• Biological half-life of radioisotopes
– Time required for 50% to disappear from the body
– Decay and physiological clearance
2-11
Ions, Electrolytes, and Free Radicals
• Ions—charged particles
with unequal number of
protons and electron
• Elements with one to
three valence electrons
tend to give up, and
those with four to seven
electrons tend to gain
• Ionization—transfer of
electrons from one
atom to another
( stability of valence
shell)
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11 protons
12 neutrons
11 electrons
Sodium
atom (Na)
17 protons
18 neutrons
17 electrons
Chlorine
atom (Cl)
1 Transfer of an electron from a sodium atom to a chlorine atom
Figure 2.4 (1)
2-12
Ions, Electrolytes, and Free Radicals
• Anion—atom that gains electrons (net negative charge)
• Cation—atom that loses an electron (net positive charge)
• Ions with opposite charges are attracted to each other
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
–
+
Figure 2.4 (2)
11 protons
12 neutrons
10 electrons
Sodium
ion (Na+)
17 protons
18 neutrons
18 electrons
Chloride
ion (Cl–)
Sodium chloride
2
The charged sodium ion (Na+) and chloride ion (Cl–) that result
2-13
Ions, Electrolytes, and Free Radicals
• Electrolytes—salts that ionize in water and form
solutions capable of conducting an electric current
• Electrolyte importance
– Chemical reactivity
– Osmotic effects (influence water movement)
– Electrical effects on nerve and muscle tissue
2-14
Ions, Electrolytes, and Free Radicals
• Electrolyte balance is one of the most important
considerations in patient care
• Imbalances have ranging effects from muscle
cramps, brittle bones, to coma and cardiac arrest
2-15
Ions, Electrolytes, and Free Radicals
2-16
Ions, Electrolytes, and Free Radicals
• Free radicals—chemical particles with an odd
number of electrons
• Produced by
– Normal metabolic reactions, radiation, chemicals
• Causes tissue damage
– Reactions that destroy molecules
– Causes cancer, death of heart tissue, and aging
• Antioxidants
– Neutralize free radicals
– In body, superoxide dismutase (SOD) converts
superoxides into water and oxygen
– In diet (selenium, vitamin E, vitamin C, carotenoids)
2-17
Water and Mixtures
• Mixtures—consist of substances physically
blended, but not chemically combined
• Body fluids are complex mixtures of chemicals
– Each substance maintains its own chemical
properties
• Most mixtures in our bodies consist of chemicals
dissolved or suspended in water
• Water 50% to 75% of body weight
– Depends on age, sex, fat content, etc.
2-18
Water
• Solvency—ability to dissolve other chemicals
• Water is called the universal solvent
– Hydrophilic—substances that dissolve in water
• Molecules must be polarized or charged
– Hydrophobic—substances that do not dissolve in
water
• Molecules are nonpolar or neutral (fat)
• Virtually all metabolic reactions depend on the
solvency of water
2-19
Water
• Water helps stabilize the internal temperature
of the body
– Has high heat capacity—the amount of heat required to
raise the temperature of 1 g of a substance by 1°C
– Calorie (cal)—the amount of heat that raises the
temperature of 1 g of water 1°C
• Hydrogen bonds inhibit temperature increases by inhibiting
molecular motion
• Water absorbs heat without changing temperature very much
– Effective coolant
• 1 mL of perspiration removes 500 calories
2-20
Measures of Concentration
• How much solute in a given volume of solution?
• Weight per volume
– Weight of solute in given volume of solution
• IV saline: 8.5 g NaCl per liter of solution
• Biological purposes: milligrams per deciliter
– mg/dL (deciliter = 100 mL)
2-21
Measures of Concentration
• Percentages
– Weight/volume of solute in solution
• IV D5W (5% w/v dextrose in distilled water)
– 5 g dextrose and fill to 100 mL water
• Molarity—known number of molecules per
volume
– Moles of solute/liter of solution
– Physiologic effects based on number of molecules in
solution not on weight
2-22
Measures of Concentration
• Molarity (M) is the number of moles of solute/
liter of solution
– MW of glucose is 180
– One-molar (1.0 M) glucose solution contains 180
g/L
2-23
Measures of Concentration
• Electrolytes are important for their chemical,
physical, and electrical effects on the body
– Electrical effects determine nerve, heart, and
muscle actions
2-24
Acids, Bases, and pH
• An acid is a proton donor (releases H+ ions in
water)
• A base is a proton acceptor (accepts H+ ions)
– Releases OH- ions in water
• pH is a measure derived from the molarity of H+
– a pH of 7.0 is neutral pH
(H+ = OH-)
– a pH of less than 7 is acidic solution (H+ > OH-)
– a pH of greater than 7 is basic solution (OH- > H+ )
2-25
Acids, Bases, and pH
• pH—measurement of molarity of H+ [H+] on a
logarithmic scale
– pH scale invented by Sören Sörensen in 1909 to
measure acidity of beer
– pH = -log [H+] thus pH = -log [10-3] = 3
• A change of one number on the pH scale
represents a 10-fold change in H+ concentration
– A solution with pH of 4.0 is 10 times as acidic as one
with pH of 5.0
2-26
Acids, Bases, and pH
• Our body uses buffers to resist changes in pH
– Slight pH disturbances can disrupt physiological
functions and alter drug actions
– pH of blood ranges from 7.35 to 7.45
– Deviations from this range cause tremors, paralysis,
or even death
2-27
Acids, Bases, and pH
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Wine,
vinegar
(2.4–3.5)
Gastric juice
(0.9–3.0) Lemon
1M
hydrochloric
acid(0)
Bananas,
tomatoes
(4.7)
Milk, Pure water
Egg white
saliva
(7.0)
(8.0)
(6.3–6.6)
Bread,
black
coffee
(5.0)
Household
bleach
(9.5)
Household
ammonia
(10.5–11.0)
Oven cleaner, lye
(13.4)
1 M sodium
hydroxide
(14)
juice
(2.3)
3
2
4
5
6
7
Neutral
8
9
10
11
12
13
1
0
14
Figure 2.12
2-28
Metabolism, Oxidation,
and Reduction
• All the chemical reactions of the body
• Catabolism
– Energy-releasing (exergonic) decomposition reactions
• Breaks covalent bonds
• Produces smaller molecules
• Releases useful energy
• Anabolism
– Energy-storing (endergonic) synthesis reactions
• Requires energy input
• Production of protein or fat
• Driven by energy that catabolism releases
• Catabolism and anabolism are inseparably linked
2-29
Carbon Compounds
and Functional Groups
• Organic chemistry—the study of compounds
containing carbon
• Four categories of carbon compounds
–
–
–
–
Carbohydrates
Lipids
Proteins
Nucleotides and nucleic acids
2-30
Monomers and Polymers
• Macromolecules—very large organic molecules
– Very high molecular weights
• Proteins, DNA
• Polymers—molecules made of a repetitive series
of identical or similar subunits (monomers)
– Starch is a polymer of about 3,000 glucose monomers
• Monomers—identical or similar subunits
2-31
Carbohydrates
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Glucose
• Three important
monosaccharides
– Glucose, galactose, and
fructose
– Same molecular formula:
C6H12O6
CH2OH
O
H
HO
Galactose
• Glucose is blood sugar
OH
H
H
OH
OH
CH2OH
O
HO
H
• All isomers of each other
– Produced by digestion of
complex carbohydrates
H
H
H
H
OH
H
H
OH
OH
Fructose
O
HOCH2
H
OH
H
OH
HO
CH2OH
H
Figure 2.16
2-32
Carbohydrates
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
• Disaccharide—sugar
molecule composed of
two monosaccharides
Sucrose
• Three important
disaccharides
Lactose
– Sucrose—table sugar
CH2OH
H
OH
H
• Glucose + galactose
– Maltose—grain products
• Glucose + glucose
CH2OH O
H
H
H
O
HO
H
HO
CH2OH
OH
OH
CH2OH
H
H
OH
OH
H
O
HO
H
OH
H
H
H
H
OH
O
H
• Glucose + fructose
– Lactose—sugar in milk
O
H
H
OH
O
H
CH2OH
Maltose
CH2OH
CH2OH
O
H
H
OH
H
HO
H
OH
H
O
H
O
H
OH
OH
H
H
H
Figure 2.17
OH
2-33
Carbohydrates
• Oligosaccharides—short chains of 3 or
more monosaccharides (at least 10)
• Polysaccharides—long chains of
monosaccharides (at least 50)
2-34
Carbohydrates
• Three polysaccharides of interest in
humans
– Glycogen: energy storage polysaccharide in
animals
• Made by cells of liver, muscles, brain, uterus, and
vagina
• Liver produces glycogen after a meal when glucose
level is high, then breaks it down between meals to
maintain blood glucose levels
• Muscles store glycogen for own energy needs
• Uterus uses glycogen to nourish embryo
2-35
Carbohydrates
• Three polysaccharides of interest in
humans (cont)
– Starch: energy storage polysaccharide in
plants
• Only significant digestible polysaccharide in the
human diet
– Cellulose: structural molecule of plant cell
walls
• Fiber in our diet
2-36
Glycogen
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CH2OH
CH2OH
O
O
O
O
CH2OH
CH2OH
CH2
O
O
(a)
O
O
O
O
CH2OH
O
O
O
O
(b)
Figure 2.18
2-37
Carbohydrates
2-38
Lipids
• Hydrophobic organic molecule
– Composed of carbon, hydrogen, and oxygen
– With high ratio of hydrogen to oxygen
• Less oxidized than carbohydrates, and thus has
more calories/gram
• Five primary types in humans
–
–
–
–
–
Fatty acids
Triglycerides
Phospholipids
Eicosanoids
Steroids
2-39
Lipids
• Triglycerides (Neutral Fats)
– Three fatty acids covalently bonded to three-carbon
alcohol called glycerol
– Each bond formed by dehydration synthesis
– Once joined to glycerol, fatty acids can no longer donate
protons— neutral fats
– Broken down by hydrolysis
• Triglycerides at room temperature
– When liquid, called oils
• Often polyunsaturated fats from plants
– When solid, called fat
• Saturated fats from animals
• Primary function: energy storage, insulation, and
shock absorption (adipose tissue)
2-40
Lipids
• Similar to neutral fat
except that one fatty
acid is replaced by a
phosphate group
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CH3
CH3 N+ CH3
CH2
CH2
Nitrogencontaining
group
(choline)
O
O
P
O
Hydrophilic region (head)
Phosphate
group
O
• Structural foundation
of cell membrane
O
CH CH2
O
O
C
C
CH
CH3
Glycerol
O
(CH2)5 (CH2)12
• Amphiphilic
– Fatty acid “tails” are
hydrophobic
– Phosphate “head” is
hydrophilic
CH2
Fatty acid
tails
CH
Hydrophobic region (tails)
(CH2)5
CH3
(a)
(b)
Figure 2.21a,b
2-41
Lipids
• Steroid—a lipid with 17 of its carbon atoms in four
rings
• Cholesterol—the “parent” steroid from which the
other steroids are synthesized
– Cortisol, progesterone, estrogens, testosterone, and bile
acids
– Synthesized only by animals
• Especially liver cells
• 15% from diet, 85% internally synthesized
– Important component of cell membranes
– Required for proper nervous system function
2-42
“Good” and “Bad” Cholesterol
• One kind of cholesterol
– Does far more good than harm
• “Good” and “bad” cholesterol actually refers to droplets
of lipoprotein in the blood
– Complexes of cholesterol, fat, phospholipid, and protein
• HDL (high-density lipoprotein): “good” cholesterol
– Lower ratio of lipid to protein
– May help to prevent cardiovascular disease
• LDL (low-density lipoprotein): “bad” cholesterol
– High ratio of lipid to protein
– Contributes to cardiovascular disease
2-43
Cholesterol
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H 3C
CH3
CH3
CH3
CH3
HO
Figure 2.23
2-44
Lipids and Functions
2-45
Proteins
• Greek word meaning “of first importance”
– Most
versatile molecules in the body
• Protein—a polymer of amino acids
• Amino acid—central carbon with three attachments
– Amino group (NH2), carboxyl group (—COOH), and radical
group (R group)
• 20 amino acids used to make the proteins are
identical except for the radical (R) group
– Properties of amino acid determined by R group
2-46
Proteins
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Some nonpolar amino acids
Some polar amino acids
Methionine
H
Cysteine
H
H
H
N
N
C
H
CH2
CH2
S
C
H
CH3
O
OH
Tyrosine
H
H
H
C
H
N
CH2
OH
H
C
O
OH
Arginine
N
H
SH
C
C
O
CH2
C
NH2+
(CH2)3
O
C
NH2
C
OH
NH
Figure 2.24a
OH
(a)
• Amino acids differ only in the R group
2-47
Proteins
• Conjugated proteins contain a non–amino
acid moiety called a prosthetic group
• Hemoglobin contains four complex ironcontaining rings called a heme moiety
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 2.25 (4)
Beta chain
Alpha
chain
Association of two or
more polypeptide chains
with each other
Heme
groups
Alpha
chain
Quaternary structure
Beta
chain
2-48
Primary Structure of Insulin
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Phe
Gly
Arg Glu
Gly
Cys
Phe
Tyr
Glu Asn Tyr
Thr
Leu
Pro
lle
Lys
Tyr
Asn
Leu
Ala
Glu
Glu
Ser
Gln
Val
Cys
Cys
Leu
lle
Cys
Ser
Val
Figure 2.26
Gly
Tyr
Val
Leu
Phe
Leu
Cys
Gln
Thr
Val
His
Thr
Ser
Asn
Gln
His Leu Cys
Gly
2-49
Proteins
• Catalysis
– Enzymes
• Recognition and protection
– Immune recognition
– Antibodies
– Clotting proteins
• Movement
– Motor proteins—molecules with the ability to change
shape repeatedly
• Cell adhesion
– Proteins bind cells together
– Immune cells to bind to cancer cells
– Keeps tissues from falling apart
2-50
Enzymes and Metabolism
• Enzymes—proteins that function as biological
catalysts
– Permit reactions to occur rapidly at normal body
temperature
• Substrate—substance an enzyme acts upon
• Naming convention
– Named for substrate with -ase as the suffix
• Amylase enzyme digests starch (amylose)
• Lowers activation energy—energy needed to get
reaction started
– Enzymes facilitate molecular interaction
2-51
Enzyme Structure and Action
• Substrate approaches active site on enzyme
molecule
• Substrate binds to active site forming enzyme–
substrate complex
– Highly specific fit—‟lock and key”
• Enzyme–substrate specificity
• Enzyme breaks covalent bonds between monomers
in substrate
2-52
Enzyme Structure and Action
• Factors that change enzyme shape
– pH and temperature
– Alters or destroys the ability of the enzyme to bind to
substrate
– Enzymes vary in optimum pH
• Salivary amylase works best at pH 7.0
• Pepsin works best at pH 2.0
– Temperature optimum for human enzymes—body
temperature (37°C)
2-53
Cofactors
• Cofactors
– About two-thirds of human enzymes require a
nonprotein cofactor
– Inorganic partners (iron, copper, zinc,
magnesium, and calcium ions)
– Some bind to enzyme and induce a change in
its shape, which activates the active site
– Essential to function
2-54
Cofactors
• Coenzymes
– Organic cofactors derived from water-soluble
vitamins (niacin, riboflavin)
– They accept electrons from an enzyme in one
metabolic pathway and transfer them to an
enzyme in another
2-55
ATP, Other Nucleotides,
and Nucleic Acids
• Three components of nucleotides
– Nitrogenous base (single or double carbon–
nitrogen ring)
– Sugar (monosaccharide)
– One or more phosphate groups
• ATP—best-known nucleotide
– Adenine (nitrogenous base)
– Ribose (sugar)
– Phosphate groups (3)
2-56
Adenosine Triphosphate
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Adenine
NH2
Adenine
NH2
C
C
N
N
C
N
N
C
CH
HC
CH
C
HC
N
N
C
N
N
Adenosine
Ribose
Ribose
Triphosphate
–O
O
O
O
P O
P O
P
–O
–O
Monophosphate
O
CH2
O
O
–O
HO
H H
OH
(a) Adenosine triphosphate (ATP)
P
CH2
O
H H
OH
O
H H
O
H H
OH
(b) Cyclic adenosine monophosphate (cAMP)
Figure 2.30a, b
ATP contains adenine, ribose, and three phosphate groups
2-57
Adenosine Triphosphate
• Body’s most important energy-transfer
molecule
• Briefly stores energy gained from exergonic
reactions
• Releases it within seconds for physiological
work
• Holds energy in covalent bonds
– Second and third phosphate groups have high
energy bonds (~)
– Most energy transfers to and from ATP involve
adding or removing the third phosphate
2-58
Adenosine Triphosphate
• Adenosine triphosphatases (ATPases)
hydrolyze the third high-energy phosphate
bond
– Separates into ADP + Pi + energy
• Phosphorylation
– Addition of free phosphate group to another
molecule
– Carried out by enzymes called kinases
(phosphokinases)
2-59
Sources and Uses of ATP
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Glucose + 6 O2
are converted to
6 CO2 + 6 H2O
which releases
energy
which is used for
ADP + Pi
ATP
which is then available for
Figure 2.31
Muscle contraction
Ciliary beating
Active transport
Synthesis reactions
etc.
2-60
ATP Production
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Glycolysis
Glucose
2 ADP + 2 Pi
Stages of
glucose
oxidation
2 ATP
Pyruvic acid
Anaerobic
fermentation
No oxygen
available
Lactic acid
Aerobic
respiration
Oxygen
available
CO2 + H2O
Mitochondrion
36 ADP + 36 Pi
• ATP consumed
within 60 seconds
of formation
• Entire amount of
ATP in the body
would support life
for less than 1
minute if it were
not continually
replenished
• Cyanide halts
ATP synthesis
36 ATP
Figure 2.32
2-61
Other Nucleotides
• Guanosine triphosphate (GTP)
– Another nucleotide involved in energy transfer
– Donates phosphate group to other molecules
• Cyclic adenosine monophosphate (cAMP)
– Nucleotide formed by removal of both second and third
phosphate groups from ATP
– Formation triggered by hormone binding to cell surface
– cAMP becomes “second messenger” within cell
– Ativates metabolic effects inside cell
2-62
Nucleic Acids
• Polymers of nucleotides
• DNA (deoxyribonucleic acid)
– 100 million to 1 billion nucleotides long
– Constitutes genes
• Instructions for synthesizing all of the body’s proteins
• Transfers hereditary information from cell to cell and generation to
generation
• RNA (ribonucleic acid)—three types
–
–
–
–
Messenger RNA, ribosomal RNA, transfer RNA
70 to 10,000 nucleotides long
Carries out genetic instruction for synthesizing proteins
Assembles amino acids in the right order to produce
proteins
2-63