Chapter 2
The Chemical Basis of
Life
Basic principles of chemistry

It is important for us to understand the
basic principles of chemistry so we can
understand how the human body is
organized.
Elements


Matter —anything that has mass and
occupies space
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
Compounds

Compound—atoms of two or more
elements joined to form chemical
combinations

List some compounds that are made up in
your body.
Atoms

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

Atomic Number

Atomic number
 The
number of protons in an atom’s nucleus
 The atomic number is critically important; it
identifies the kind of element
Atomic Weight

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)
Basic Chemistry

Energy levels
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

Basic Chemistry

Isotopes
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

Molecules and Compounds
Molecule—two or more atoms joined together
 Compound—consists of molecules formed by
atoms of two or more elements

Three types of bonds
Covalent—formed by sharing of electron
pairs between atoms
 Ionic—formed by transfer of electrons;
strong electrostatic force that binds
positively and negatively charged ions
together
 Hydrogen---much weaker than ionic or
covalent bonds results from unequal
charge distribution on molecules

Three chemical reaction in human
physiology

1)
2)
3)
There are three main chemical reactions
in human physiology:
Synthesis reaction
Decomposition reaction
Exchange reaction
Synthesis reaction
 Synthesis
reaction—combining of two or more
substances to form a more complex substance;
formation of new chemical bonds: A + B → AB
Example:
Amino Acid + Amino Acid → Protein
Decomposition reaction
 Decomposition
reaction—breaking down of a
substance into two or more simpler substances;
breaking of chemical bonds: AB → A + B
Example:
ATP → ADP + P + Energy (Heat)
Exchange reaction
 Exchange
reaction—decomposition of two
substances and, in exchange, synthesis of two
new compounds from them: AB + CD → AD + CB
Example:
H*Lactate + NaHCO3 → Na*Lactate + H*HCO3
Metabolism

Metabolism—all of the chemical
reactions that occur in body cells
There are two types of metabolism:
-Catabolism
-Anabolism


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 228)
Metabolism

Anabolism
Chemical reactions that join simple molecules
together to form more complex molecules
 Chemical reaction responsible for anabolism
is dehydration synthesis

Organic vs. Inorganic Molecules

Organic molecules is
a compound that
contains carbon—
specifically C-C or
C-H bond

Inorganic
compounds—few
have carbon atoms
and none have C–C
or C–H bonds
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)
Properties of water
Polarity—allows water to act as an effective
solvent; ionizes substances in solution
 The solvent allows transportation of essential
materials throughout the body



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
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

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

Inorganic Compounds

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”
Organic Compounds
There are 4 major organic compounds
that are important to humans:
Macromolecules:
1) Carbohydrates
2) Proteins
3) Lipids
4) Nucleic Acids

Carbohydrates

1)
2)
3)
There are three main carbohydrates:
Monosaccharides (simple sugars)
Disaccharides (double sugars)
Polysaccharides (complex sugars)
Carbohydrates

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)

Disaccharides and polysaccharides—two (di-) or
more (poly-) simple sugars that are bonded
together through a synthesis reaction
Proteins

Most abundant organic compounds

Chainlike polymers

Amino acids—building blocks of proteins

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
Organic Molecules

Lipids
Water-insoluble organic molecules that are
critically important biological compounds
 Major roles:

 Energy
source
 Structural role
 Integral parts of cell membranes
Lipids
Triglycerides, or fats
 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
Lipids

Phospholipids
 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
Lipids

Steroids
 Main
component is steroid nucleus
 Involved in many structural and functional roles
Nucleic acids
There are two types of nucleic acids:
 1) DNA
 2) RNA

Nucleic Acids

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
 Alternating deoxyribose and phosphate units form
backbone of the chains
Nucleic Acids
Base pairs hold the two chains of DNA
molecule together
 DNA functions as the molecule of heredity

Nucleic Acids

RNA (ribonucleic acid) (Figure 2-29, Table 27)
 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)
Similarities and Difference of DNA
and RNA
Have similar
nucleotides:
Adenine (A)
Guanine (G)
Cytosine (C)

Differences:
-Double helix vs. single
helix
-Ribose sugar vs.
deoxyribose sugar
-RNA has a nucleotide
of Uracil and DNA
has a nucleotide of
thymine

Energy

Adenosine triphosphate (ATP)- transfers
energy from one chemical pathway to
another. It is composed of one adenine
molecule and three phosphate molecules.