Chapter 2
Chemistry
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chemistry
• Scientific study of substances (chemicals)
and how they interact with each other
• The human body is made out of chemicals
• Processes of life are chemical interactions
2.1 Atoms and Elements
• Matter is anything that has weight and
occupies space
• Matter is composed of chemical elements
• Chemical elements
– Substances that cannot be broken down by
chemical means into simpler substances
• Examples: carbon, hydrogen, nitrogen
– 92 naturally occurring
– 26 found in the human body
• Atomic Structure
– An atom is the smallest unit of an element
that participates in chemical reactions
– Atoms of the same element are similar
– Atoms of different elements differ in size,
weight, and how they interact with other
atoms
– Atoms are
composed of
three subatomic
particles
• Protons
• Neutrons
• Electrons
– The overall
electrical charge
of an atom is
neutral
• number of protons
= number of
electrons
2.2 Molecules and Compounds
• A molecule is 2 or more atoms chemically
combined
– Examples: O2, NaCl
– Smallest unit of a chemical compound that
exhibits the properties of the compound
• A chemical compound is a substance
composed of 2 or more elements chemically
combined in a fixed ratio
• Chemical Formulas
– Uses chemical symbols to express the
chemical composition of a molecule
– Example: H2O: 2 atoms of hydrogen, 1
atom of oxygen
• Chemical Bonds
– Force of attraction between 2 atoms that
allows them to join and form a molecule
– Atoms combine to fill their valence shells
and become more stable
– 3 types of chemical bonds
• Ionic bonds
• Covalent bonds
• Hydrogen bonds
• Ionic Bonds
– Chemical bond formed between 2 ions
with opposing electrical charge
• Anions
• Cations
– Once a cation and anion are formed, the
opposing electrical charges create a force
that holds the ions together
• The force is the ionic bond!
– Ionic compounds dissociate when they
dissolve in water
• Called electrolytes because they can conduct
electrical current in water
• Composition and concentration of electrolytes
must be kept within narrow limits for normal
body function
• Chemical Reactions
– Occur when bonds between atoms form or
break, yielding new combinations of atoms
– Two main types of reactions
• Synthesis reactions
• Decomposition reactions
– Many reactions are reversible
2.3 Compounds Composing
the Human Body
• Human body is made out of 2 types of
compounds:
• Inorganic – do not contain both carbon
and hydrogen
• Organic – contain both carbon and
hydrogen
Major Inorganic Compounds
• Water
– Composes 2/3 of body weight
– Absorbs/releases large amounts of heat
without much of a change in temperature
– Solvent for many solutes
– Site of chemical reactions in the body
• Water
– Serves as a lubricant
– Assists in movement of food through the
digestive tract
– Water compartments in the body
• Intracellular fluid
• Extracellular fluid
–
–
–
–
Tissue (interstitial fluid)
Plasma
Lymph
Specialized fluids
• Acids and Bases
– Acids increase hydrogen ion concentration
of a solution by releasing H+
– Bases decrease the concentration of H+ by
combining with the H+ already in the
solution
– pH is the measure of how basic or acidic a
solution is
– pH Scale indicates the acidity or alkalinity of
a solution (relative concentrations of H+ and
OH-)
• Ranges from 0-14
• pH 7 is neutral, meaning equal H+ and OHconcentrations
• >pH 7 is a base; higher number means stronger
base
• <pH 7 is an acid; lower number means stronger
acid
– Buffers
• Chemical or chemicals that can either pick up
or release H+ to keep a solution’s pH constant
• Maintain normal PH of body fluids
• Needed because slight pH changes can be
harmful to body cells
• Salts
– Ionic compounds that dissociate in water
but do not produce H+ or OH- ions
• Example: NaCl dissociates to Na+ and Cl-
– Provide ions essential for normal body
functioning
– Example of salts: sodium, potassium,
calcium salts
Major Organic Compounds
• Carbohydrates
– Formed of carbon, oxygen, and hydrogen
• 2 H for every O
– Primary source of nutrient energy for body
cells
– Classified by molecular size
• Monosaccharides- ex. glucose
• Disaccharides• Polysaccharides
– Monosaccharides or simple sugars
• Simplest carbohydrates
• Glucose (C6H12O6) is major fuel for cells
• Fructose and galactose are 6-C simple sugars
found in foods
– Disaccharides
• Formed by chemically combining 2
monosaccharides
• Maltose
• Sucrose
• Lactose
– Polysaccharides
• Formed by chemically combining many
monosaccharides
• Glycogen: animal carbohydrate storage
• Starch: plant carbohydrate storage
• Lipids
– Consist of carbon, hydrogen, and oxygen
atoms
• C atoms form backbone of molecules
• Many more H atoms then O atoms
– Most abundant in the body are
• Triglycerides
• Phospholipids
• Steroids
– Triglycerides
•
•
•
•
Most concentrated energy source in the body
Around internal organs and under the skin
Hydrophobic
One glycerol molecule and 3 fatty acid
molecules joined together
• Saturated fats
– Animal triglycerides or
fats
– All C-C bonds are single
bonds
– Solid at room
temperature
– Examples: butter, lard
• Unsaturated fats
– Plant triglycerides or oils
– One or more double C-C
bonds
– Monounsaturated
– Polyunsaturated
– Examples: olive oil, corn oil
– Phospholipids
• Composed of 1 glycerol, 2 fatty acid, and 1
phosphate group
• Hydrophilic
• Major components of cell membranes
– Steroids
• Molecules containing 4 C rings
• Cholesterol, a steroid and cell component, is
used to make other steroids
• Proteins
– Amino acids are the building units of proteins
• Composed of carbon, hydrogen, oxygen, and nitrogen
• Consist of an amine group, acid group, and R group
• 20 different types of amino acids, each different in
their R group
– Amino acids are joined by peptide bonds
• Dipeptide
• Polypeptide
– Each polypeptide or protein has a unique
three-dimensional shape
– Classification of proteins
• Structural
• Functional
– Enzymes are proteins
• One enzyme catalyzes one particular chemical reaction
• Aid in the conversion of a substrate into a product
• Loss of an enzyme’s specific 3-D structure inactivates it
• Nucleic Acids
– Two types in cells
• Deoxyribonucleic acid
(DNA)- stores genetic
information
• Ribonucleic acid
(RNA)- involved in
protein synthesis
– Building blocks are
called nucleotides
• Composed of 1 C5
sugar, 1 phosphate, 1
organic base
• Adenosine Triphosphate (ATP)
– Modified nucleotide with adenosine and 3
phosphates
– Temporarily stores energy extracted from
nutrients by cells
– Only molecule to provide immediate
energy to keep cellular processes going
(powers chemical reactions)