Anatomy and Physiology
Chapter 2: The Chemical Basis of Life
Basic Chemistry
Elements and compounds
• Matter—anything that has mass and occupies space
• Element—simple form of matter, cannot be broken down
• 26 elements in the human body
• 11 major elements, 4 make up 96% of the human body
• Rest make up 2% of body (Trace elements)
• Compound—atoms of two or more elements joined to form chemical combinations
Four elements make up about 96% of human body weight.
 Oxygen
65.0%
 Carbon
18.5%
 Hydrogen
9.5%
 Nitrogen
3.2%
Basic Chemistry
 Atoms: concept of an atom was proposed by the English chemist John Dalton
 Atomic structure—3 subatomic particles
-Protons (p)—positively charged found in the nucleus
-Neutrons (n)—neutral found in the nucleus
-Electrons (e)—negatively found in the electron cloud
Atomic number and mass number
 Atomic number
o Equal to number of protons
o Identifies the kind of element
 Mass number
o Mass of a single atom
 (p + n)
Isotopes
• same number of protons but different numbers of neutrons
• have a different mass number
 Radioactive isotope (radioisotope)—an unstable isotope that undergoes nuclear breakdown and
emits nuclear particles and radiation
• Used in diagnostics & treatments due to radioactive properties
• Target tissue
• Shortest half life
• Radiation sickness: mild to severe or even fatal.
• Depends on exposure
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Mild: Nausea, headaches
Extreme: Leukemia, Sterility, birth defects, skin damage
Chemical bond: The electrical attraction between atoms
 Three types of chemical bonds
o Ionic bond: Caused by a transfer of electrons between atoms
o Covalent bond: Involves a sharing of electrons by the outer shells of the atom
 Strength goes up with shared bonds
 Unequal charge distribution on molecules (Polarity)
o Hydrogen bond: An intermolecular attraction, no transfer of electrons
 weakest of bonds
Metabolism: all of the chemical reactions that occur in body cells (2 main types)
 Catabolism
o Chemical reactions break down complex compounds into simpler ones and
release energy
 E.g.: hydrolysis is a common catabolic reaction
 Uses water to break down things
 Products of catabolism are carbon dioxide, water, and other
waste products
 Releases ATP
 Anabolism
o Use simple molecules together to build complex molecules
o Dehydration synthesis (condensation)
 Joins two things and loses water
o Requires ATP
Organic and Inorganic Compounds
 Inorganic compounds-few have carbon atoms and none have C—C or C—H bonds
o Water
 Most abundant compound in the body
 Properties of water
 Polarity: effective solvent in the body
 Ionizes substances in solution
 Lubricant
 Transport medium
 Protection/Cushioning
o Oxygen and carbon dioxide—needed for cellular respiration
 Oxygen—necessary for the release of energy in the body
 Carbon dioxide—waste product and helps maintain acid-base balance in the
body
o Electrolytes
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Large group includes acids, bases, and salts
Form ions (called electrolytes).
 Cations: Na+, K+
 Anions: Cl-, I-
Acids and bases—chemical opposites
 Acids
o Any substance that releases a hydrogen ion (H+) when in solution—proton donor
o Level of acidity depends on the number of hydrogen ions a particular acid will release
 Bases
o Dissociate to yield hydroxide ions (OH-) or other electrolytes that combine with
hydrogen ions (H+)
o Described as proton acceptors
pH scale—assigns a value to measures of acidity and alkalinity
 Scaled from 0-14
 pH of 7 indicates neutrality (equal amounts of H+ and OH-)
 pH less than 7 indicates acidity
 pH higher than 7 indicates alkalinity
Buffers
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Salts
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Maintain the constancy of pH
Minimize changes in the concentrations of H+/OH- ions
Results from chemical interaction of an acid and a base
o Called a neutralization reaction
Organic compounds:
o A least one carbon atom & at least 1 C–C or C–H bond in each molecule
o Functional groups attached to the molecule
 Carbohydrates- contains C, H, and O(usual ratio 1:2:1)
o Called sugars and starches
 Monosaccharaides simple sugars with short carbon chains
 Glucose
 Fructose
 Galactose
 Disaccharides two (di-)
 Sucrose: (glucose + fructose)
 Maltose: (glucose + glucose)
 Lactose: (glucose + galactose)
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Polysaccharidesmore (poly-) simple sugars that are bonded together
 Glycogen (animal)
 Starch (plants)
Lipids: water-insoluble important for compounds: Fats, Steroids, Prostaglandins, &
Phospholipids
o Major roles:
 Energy source
 Cushioning for internal organs
 Integral parts of cell membranes
o Fatty acids
 Most abundant of lipids and most concentrated source of energy
 Types of fatty acids:
 Saturated fatty acid (all available bonds are filled)
o Animal fats
o Solid at Room Temp
 Unsaturated fatty acid (has one or more double bonds)
o Plant oils
o Liquid at room temp
o Can be broken down faster which means they are “healthier”
 Phospholipids
o One end is water soluble (hydrophilic)
o Other end is fat soluble (hydrophobic)
o Can join two different chemical environments
o Form double layers called bilayers that make up cell
membranes
 Steroids (sterols)
o Structural and functional roles
o Cholesterol: needed to survive
 ONLY ANIMALS CONTAIN CHOLESTEROL not plants
 Prostaglandins
o Tissue hormones: produced by cell membranes throughout the
body
o Response to a specific stimulus and then inactivated
Protein: Most abundant organic compounds, Amino acids form peptide bonds
 All contain C, H, O, and N
 Functional:
o Enzymes: Anything ending in –ase is an enzyme
o Antibodies
o Hormones
 Amino acids—building blocks of proteins
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Essential amino acids
o 8 amino acids that cannot be produced by the adult human body
 Nonessential amino acids
o 13 amino acids can be produced in the adult human body
Nucleic acids and related molecules
 DNA (De-oxy-ribo-Nucleic Acid)
o 2 chains of deoxyribonucleotides coiled into a double-helix shape
o (twisted ladder)
 RNA (Ribonucleic Acid)
o Single strand, DNA copies
o Make proteins