Download Chapter 7 Body Systems

Chapter 2
The Chemical Basis of Life
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Slide 1
Basic Chemistry
• Elements and compounds (Figure 2-1)

Matter—anything that has mass and
occupies space
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Slide 2
Basic Chemistry
• Element—simple form of matter, a substance that
cannot be broken down into two or more different
substances

There are 26 elements in the human body

There are 11 “major elements,” four of which (carbon,
oxygen, hydrogen, and nitrogen) make up 96% of the human
body

There are 15 “trace elements” that make up less than 2% of
body weight
• Compound—atoms of two or more elements joined to
form chemical combinations
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Slide 3
Basic Chemistry
• Atoms (Figure 2-2)

The concept of an atom was proposed by the
English chemist John Dalton
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Slide 4
Basic Chemistry
• Atomic structure—atoms contain several different
kinds of subatomic particles; the most important are
the following:

Protons (+ or p)—positively charged subatomic particles
found in the nucleus

Neutrons (n)—neutral subatomic particles found in the
nucleus

Electrons (– or e)—negatively charged subatomic particles
found in the electron cloud
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Slide 5
Basic Chemistry
• Atomic number and atomic weight

Atomic number (Table 2-1)
• The number of protons in an atom’s nucleus
• The atomic number is critically important; it identifies the kind of
element

Atomic weight
• The mass of a single atom
• It is equal to the number of protons plus the number of neutrons
in the nucleus (p + n)
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Slide 6
Basic Chemistry
• Energy levels (Figures 2-3 and 2-4)

The total number of electrons in an atom equals
the number of protons in the nucleus
(in a stable atom)

The electrons form a “cloud” around the nucleus
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Slide 7
Basic Chemistry
• Energy levels (cont.)

“Bohr model”—a model resembling planets revolving around
the sun, useful in visualizing the structure of atoms
• Exhibits electrons in concentric circles showing relative distances
of the electrons from the nucleus
• Each ring or shell represents a specific energy level and can hold
only a certain number of electrons
• The number and arrangement of electrons determine if an atom is
chemically stable
• An atom with eight, or four pairs of, electrons in the outermost
energy level is chemically inert
• An atom without a full outermost energy level is chemically active
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Slide 8
Basic Chemistry
• Energy levels (cont.)

Octet rule—atoms with fewer or more than eight
electrons in the outer energy level will attempt to
lose, gain, or share electrons with other atoms to
achieve stability
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Slide 9
Basic Chemistry
• Isotopes (Figure 2-5)

Isotopes of an element contain the same number of protons
but contain different numbers of neutrons

Isotopes have the same atomic number, and therefore the
same basic chemical properties, as any other atom of the
same element, but they have a different atomic weight

Radioactive isotope—an unstable isotope that undergoes
nuclear breakdown and emits nuclear particles and radiation
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Slide 10
Basic Chemistry
• Attractions between atoms—chemical bonds

Chemical reaction—interaction between two or
more atoms that occurs as a result of activity
between electrons in their outermost energy levels

Molecule—two or more atoms joined together

Compound—consists of molecules formed by
atoms of two or more elements
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Slide 11
Basic Chemistry
• Chemical bonds—two types unite atoms into
molecules:

Ionic, or electrovalent, bond (Figure 2-6)—formed
by transfer of electrons; strong electrostatic force
that binds positively and negatively charged ions
together

Covalent bond (Figure 2-7)—formed by sharing of
electron pairs between atoms
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Slide 12
Basic Chemistry
• Hydrogen bond (Figures 2-8 and 2-9)

Much weaker than ionic or covalent bonds

Results from unequal charge distribution on
molecules
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Slide 13
Basic Chemistry
• Attractions between molecules

Hydrogen bonds
• Form when electrons are unequally shared

Example: water molecule

Polar molecules have regions with partial electrical
charges resulting from unequal sharing of electrons among
atoms
• Areas of different partial charges attract one another,
forming hydrogen bonds
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Slide 14
Basic Chemistry
• Attractions between molecules

Other weak forces attract molecules to each other
through differences in electrical charge
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Slide 15
Basic Chemistry
• Chemical reactions

Involve the formation or breaking of chemical bonds

There are three basic types of chemical reactions
involved in physiology:
• Synthesis reaction—combining of two or more substances to form a more
complex substance; formation of new chemical bonds: A + B → AB
• Decomposition reaction—breaking down of a substance into two or more
simpler substances; breaking of chemical bonds: AB → A + B
• Exchange reaction—decomposition of two substances and, in exchange,
synthesis of two new compounds from them: AB + CD → AD + CB
• Reversible reactions—occur in both directions
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Slide 16
Metabolism
• Metabolism—all of the chemical reactions
that occur in body cells (Figure 2-10)
• Catabolism

Chemical reactions that break down complex
compounds into simpler ones and release energy;
hydrolysis is a common catabolic reaction

Ultimately, the end products of catabolism are
carbon dioxide, water, and other waste products

More than half the energy released is transferred
to ATP, which is then used to do cellular work
(Figure 2-28)
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Slide 17
Metabolism
• Anabolism

Chemical reactions that join simple molecules
together to form more complex molecules

Chemical reaction responsible for anabolism is
dehydration synthesis
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Slide 18
Organic and Inorganic Compounds
• Inorganic compounds—few have carbon
atoms and none have C–C or C–H bonds
• Organic molecules

Have at least one carbon atom and at least one
C–C or C–H bond in each molecule

Often have functional groups attached to the
carbon-containing core of the molecule
(Figure 2-11)
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Slide 19
Inorganic Compounds
• Water

The body’s most abundant and important
compound

Properties of water (Table 2-2)
• Polarity—allows water to act as an effective solvent;
ionizes substances in solution (Figure 2-8)
• The solvent allows transportation of essential materials
throughout the body (Figure 2-12)
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Slide 20
Inorganic Compounds
• Properties of water (cont.)

High specific heat—water can lose and gain large
amounts of heat with little change in its own
temperature; enables the body to maintain a
relatively constant temperature

High heat of vaporization—water requires
absorption of significant amounts of heat to
change water from a liquid to a gas, allowing the
body to dissipate excess heat
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Slide 21
Inorganic Compounds
• Oxygen and carbon dioxide—closely related
to cellular respiration

Oxygen—required to complete decomposition
reactions necessary for the release of energy in
the body

Carbon dioxide—produced as a waste product,
also helps maintain the appropriate acid-base
balance in the body
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Slide 22
Inorganic Compounds
• Electrolytes

Large group of inorganic compounds, which
includes acids, bases, and salts

Substances that dissociate in solution to form ions

Positively charged ions are cations; negatively
charged ions are anions
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Slide 23
Inorganic Compounds
• Electrolytes (cont.)

Acids and bases—common and important chemical substances
that are chemical opposites
• Acids

Any substance that releases a hydrogen ion (H+) when in solution;
“proton donor”

Level of “acidity” depends on the number of hydrogen ions a particular
acid will release
• Bases

Electrolytes that dissociate to yield hydroxide ions (OH–)
or other electrolytes that combine with hydrogen ions (H+)

Described as “proton acceptors”
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Slide 24
Inorganic Compounds
• pH scale—measuring acidity and alkalinity
(Figure 2-13)

pH indicates the degree of acidity or alkalinity of a
solution

pH of 7 indicates neutrality (equal amounts of H+
and OH–); a pH of less than 7 indicates acidity; a
pH of more than 7 indicates alkalinity
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Slide 25
Inorganic Compounds
• Buffers

Maintain the constancy of the pH

Minimize changes in the concentrations of H+
and OH– ions

Act as a “reservoir” for hydrogen ions
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Slide 26
Inorganic Compounds
• Salts (Table 2-3)

Compounds that result from chemical interaction
of an acid and a base

Reaction between an acid and a base to form a
salt and water is called a neutralization reaction
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Slide 27
Organic Molecules
(Figure 2-14; Table 2-4)
• “Organic” describes compounds that contain C–C
or C–H bonds
• Carbohydrates—organic compounds containing
carbon, hydrogen, and oxygen; commonly called
sugars and starches

Monosaccharides—simple sugars with short carbon
chains; those with six carbons are hexoses (e.g.,
glucose), whereas those with five are pentoses (e.g.,
ribose, deoxyribose) (Figure 2-15)

Disaccharides and polysaccharides—two (di-) or more
(poly-) simple sugars that are bonded together through
a synthesis reaction (Figure 2-16)
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Slide 28
Organic Molecules
• Proteins (Table 2-5)

Most abundant organic compounds

Chainlike polymers

Amino acids—building blocks of proteins
(Figures 2-17 to 2-19)
• Essential amino acids—eight amino acids that cannot be
produced by the human body
• Nonessential amino acids—12 amino acids can be
produced from molecules available in the human body
• Amino acids consist of a carbon atom, an amino group, a
carboxyl group, a hydrogen atom, and a side chain
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Slide 29
Organic Molecules
• Levels of protein structure (Figure 2-20)

Protein molecules are highly organized and show a definite
relationship between structure and function

There are four levels of protein organization:
• Primary structure—refers to the number, kind, and sequence of
amino acids that make up the polypeptide chain
• Secondary structure—polypeptide is coiled or bent into pleated
sheets stabilized by hydrogen bonds
• Tertiary structure—a secondary structure can be further twisted,
resulting in a globular shape; the coils touch in many places and are
“welded” by covalent and hydrogen bonds
• Quaternary structure—highest level of organization occurring when
protein contains more than one polypeptide chain

Two broad categories
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Slide 30
Organic Molecules
• Structural proteins form the structures of the body
• Functional proteins cause chemical changes in the
molecules

Shape of a protein’s molecules determines its function (Figure 221)
• Denatured proteins have lost their shape and therefore their function
(Figure 2-22)
• Proteins can be denatured by changes in pH, temperature, radiation,
and other chemicals
• If the chemical environment is restored, proteins may be renatured
and function normally
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Slide 31
Organic Molecules
• Lipids (Table 2-6)

Water-insoluble organic molecules that are
critically important biological compounds

Major roles:
• Energy source
• Structural role
• Integral parts of cell membranes
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Slide 32
Organic Molecules
• Lipids (cont.)

Triglycerides, or fats (Figures 2-23 and 2-24)
• Most abundant lipids and most concentrated source of energy
• The building blocks of triglycerides are glycerol (the same for
each fat molecule) and fatty acids (different for each fat, they
determine its chemical nature)

Types of fatty acids—saturated fatty acid (all available bonds are
filled) and unsaturated fatty acid (has one or more double bonds)

Triglycerides are formed by a dehydration synthesis
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Slide 33
Organic Molecules
• Lipids (cont.)

Phospholipids (Figure 2-25)
• Fat compounds similar to triglyceride
• One end of the phospholipid is water-soluble
(hydrophilic); the other end is fat-soluble (hydrophobic)
• Phospholipids can join two different chemical
environments
• Phospholipids may form double layers called bilayers
that make up cell membranes
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Slide 34
Organic Molecules
• Lipids (cont.)

Steroids (Figure 2-26)
• Main component is steroid nucleus
• Involved in many structural and functional roles
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Slide 35
Organic Molecules
• Lipids (cont.)

Prostaglandins (Figure 2-27)
• Commonly called “tissue hormones”; produced by cell
membranes throughout the body
• Effects are many and varied; however, they are released
in response to a specific stimulus and are then
inactivated
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Slide 36
Organic Molecules
• Nucleic acids and related molecules

DNA (deoxyribonucleic acid)
• Composed of deoxyribonucleotides; that is, structural
units composed of the pentose sugar (deoxyribose),
phosphate group, and nitrogenous base (cytosine,
thymine, guanine, or adenine)
• DNA molecule consists of two long chains of
deoxyribonucleotides coiled into double-helix shape
(Figure 2-28)
• Alternating deoxyribose and phosphate units form
backbone of the chains
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Slide 37
Organic Molecules
• DNA (cont.)

Base pairs hold the two chains of DNA molecule
together

Specific sequence of more than 100 million base
pairs constitute one human DNA molecule; all
DNA molecules in one individual are identical and
different from those in all other individuals

DNA functions as the molecule of heredity
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Slide 38
Organic Molecules
• Nucleic acids and related molecules (cont.)

RNA (ribonucleic acid) (Figure 2-29, Table 2-7)
• Composed of the pentose sugar (ribose), phosphate
group, and a nitrogenous base
• Nitrogenous bases for RNA are adenine, uracil, guanine,
or cytosine (uracil replaces thymine)
• Some RNA molecules are temporary copies of segments
(genes) of the DNA code and are involved in
synthesizing proteins
• Some RNA molecules are regulatory, acting as enzymes
(ribozymes) or silencing gene expression
(RNA interference)
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Slide 39
Organic Molecules
• Nucleic acids and related molecules (cont.)

Nucleotides
• Nucleotides have other important roles in the body
• ATP (Figure 2-30)

Composed of
– Adenosine
– Ribose—a pentose sugar
– Adenine—a nitrogen-containing molecule
– Three phosphate subunits
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Slide 40
Organic Molecules
• Nucleotides (cont.)
• High-energy bonds present between phosphate groups
• Cleavage of high-energy bonds releases energy during
catabolic reactions
• Energy stored in ATP is used to do the body’s work
• ATP often called the energy currency of cells
• ATP is split into adenosine diphosphate (ADP) and an inorganic
phosphate group by a special enzyme
• If ATP is depleted during prolonged exercise, creatine
phosphate (CP) or ADP can be used for energy
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Slide 41
Organic Molecules
• Nucleic acids and related molecules (cont.)

NAD and FAD (Figure 2-31)
• Used as coenzymes to transfer energy-carrying
molecules from one chemical pathway to another

cAMP (cyclic AMP)
• Made from ATP by removing two phosphate groups to
form a monophosphate
• Used as an intracellular signal
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Slide 42
Organic Molecules
• Combined forms—large molecules can be
joined together to form even larger molecules

Gives the molecules a completely different
function

Names of combined molecules reveals what is in
them
• Base word tells which component is dominant
• Prefix shows the component present in a lesser amount
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Slide 43
Organic Molecules
• Combined forms (cont.)

Examples:
• Adenosine triphosphate (ATP)—two extra phosphate
groups to a nucleotide
• Lipoproteins—lipid and protein groups combined into a
single molecule
• Glycoproteins—carbohydrate (glyco, “sweet”) and protein
• Examples of combined forms and their functions in the
body shown in Table 2-4
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Slide 44