Chemical Bonds
• The interaction between 2 atoms may result in the
formation of a chemical bond whereby 2 atoms are
chemically linked to one another
– 2 major types
• Ionic
• Covalent
• Atoms bond with one another to become stable
– an atom is stable when the valence shell is
completely full (satisfying the “octet rule”)
• Groups of atoms that are associated with each other
through bonds are called molecules
– chemicals that are LARGER and structurally more
CoMpLe
X
than individual atoms
Molecules
• Molecules
– two or more atoms bonded together
• carbon dioxide (CO2), Glucose (C6H12O6), water
(H2O), sodium chloride (NaCl)…
Nonpolar and Polar Molecules
• Nonpolar molecules include those containing a
high number of nonpolar covalent bonds and few
polar covalent bonds (very little or no O and/or N)
– lipids (fats)
• uncharged (neutral) molecules
• Polar molecules include those containing a
moderate number of polar covalent bonds
(moderate amounts of O and/or N)
• include every other substance:
– carbohydrates, proteins, nucleic acids, water…
– ions (cations and anions)
• charged molecules
Hydrogen Bonds
• Electrical attraction between a polar covalently bound
H (has a partial positive charge) and a covalently
bound electronegative atom (O/N) (has a partial
negative charge)
• Too weak to bind atoms together
– serve as intramolecular (within molecule) bonds
• aids in the stabilization of very large molecules
• observed in proteins and nucleic acids
– serve as intermolecular (between molecules) bonds
• holds 2 or more molecules in close proximity to
one another
• observed in between water molecules
Hydrogen Bonds in Water (intermolecular)
Water
• The most abundant molecule of the human body
– 70% of body mass (weight) is attributed to water
• Polar substances mix easily with other polar
substances, but do not mix with nonpolar substances
(REMEMBER THIS)
• Nonpolar substances mix easily with other nonpolar
substances, but do not mix with polar substances
(REMEMBER THIS)
– like dissolves like
• The majority of the chemicals found in the body are
polar, however lipids are molecules essential for
proper functioning of the body
Polarity (Water vs Lipids)
• All polar chemicals mix with water and are considered
to be hydrophilic (water loving)
– polar chemicals that mix with water will not mix with
lipids and are considered to be lipophobic (lipid
fearing)
• All nonpolar chemicals mix with lipids and are
considered to be lipophilic (lipid loving)
– Nonpolar chemicals that associate with lipids will
not mix with water and are considered to be
hydrophobic (water fearing)
• Polar = hydrophilic = lipophobic
• Non-polar = hydrophobic = lipophilic
Properties of Water
• Solvency
– ability to dissolve matter
• because water is the most abundant compound
in the body it is the universal solvent
• environment for all metabolic reactions
• provides a means for the transport of substances
from one location in the body to another
• Adhesion and Cohesion
– molecules of water “stick” to themselves and other
types of molecules
• due to hydrogen bonds
• High heat capacity
• prevents rapid increases or decreases in
temperature
Biochemical Reactions
• The functioning of the body (physiology) occurs as the
organic molecules of the body react with one another
• Written symbolically with chemical equations
– relative amounts of reactants (starting chemicals)
and products (finishing chemicals)
– number and type of reacting substances, and
products produced
• C6H12O6 + 6O2  6H2O + 6CO2
• Chemical reactions occur when covalent bonds in a
molecule are formed or broken
– the formation of a covalent bond uses energy
– the breaking of a covalent bond releases energy
• All chemical reactions are theoretically reversible
A + B ↔ AB CO2 + H2O ↔ H2CO3 ↔ HCO3- + H+
Work and Energy
• Energy
– capacity to do work
• Kinetic energy
– energy of motion
• Potential energy
– energy due to object’s position
Energy Sources
• Energy sources that the body uses includes:
– Chemical
• stored in the covalent bonds of energy-rich
molecules (potential)
– Electrical
• the movement of ions (potential and kinetic)
– Heat
• causes molecules to move (kinetic)
– Mechanical
• moving molecules collide with one another which
transfers energy between the two molecules
(kinetic)
• Energy sources can be converted from one form
to another
Metabolism and Biochemical Reactions
• All of the collective biochemical reactions of the body
are grouped into two general classes:
– Catabolic (exergonic) reactions
• decomposition reactions that release energy (due
to bonds breaking) in the form of HEAT into the
environment of the reaction
• reactants contain more energy than the products
– Anabolic (endergonic) reactions
• synthesis reactions that remove (store) energy
(HEAT) from the environment of the reaction to
create bonds
• products contain more energy than the reactants
• All reactions must overcome the activation energy
before the reaction takes place
– energy required to bring reactants together
Energy Flow in an Exergonic Reaction
Organic Molecules
• Molecules unique to living systems contain carbon and
are referred to as organic molecules
• Most of the anatomy and physiology of the body is
provided by the interaction between 4 different classes
of organic macromolecules
• Each class consists of small molecular subunits called
monomers (one unit)
– smallest subunits of macromolecules that exhibit
chemical properties of the macromolecule
• Monosaccharide (carbohydrates)
• Fatty acid (lipids)
• Amino acid (proteins)
• Nucleotide (nucleic acids)
– able to function individually or in covalently bound
groups
Biologically Important Organic Molecules
• Monosaccharides
– basic (smallest) unit of carbohydrates (sugars)
• Amino acids
– basic (smallest) unit of proteins
• Fatty acids
– basic (smallest) unit of lipids (fats)
• Nucleotides
– basic (smallest) unit of nucleic acids
Synthesis Reactions of Macromolecules
• Monomers can be covalently bound
to one another to create a molecule
gets progressively larger resulting
in a polymer (many units)
• Two or more small molecules
combine to form a larger one
• A+B  AB+C  ABC+D  ABCD…
Dehydration Synthesis
• 2 monomers are covalently bonded together to form a
a new molecule that is larger and structurally more
complex by the removal of a water molecule
(dehydration)
Decomposition Reactions
• Large polymer molecules can be
reduced down to the individual
monomers by breaking the covalent
bond between monomers through a
decomposition reaction
• ABC  AB+C  A+B+C
Hydrolysis
• Splitting a polymer by the addition of a water molecule
Exchange Reactions
• Two molecules collide and
exchange atoms or group of
atoms
• AB+CD  ABCD  AC + BD
Oxidation-Reduction (Redox) Reactions
• Involves the transfer of electrons from one
atom/molecule to another
– eg. formation of an ionic bond
• Reactants losing electrons are become oxidized (Loss
Electron(s) Oxidation = LEO)
• Reactants gaining electrons are become reduced
(Gain Electron(s) Reduction = GER)
• Na + Cl → Na+ + Cl– Na is oxidized and Cl is reduced
Reaction Rates
• The rate of chemical reactions are determined by
molecular motion and collisions between chemicals
• The speed at which a chemical reaction proceeds is
affected by:
– the concentration of reactants
• more concentrated = more collisions = faster rate
– the temperature
• higher temperature = faster molecular movement
= more collisions = faster rate
– the presence of catalysts
• “molecular matchmakers”
–bring reactants together faster
• biological catalysts are proteins called enzymes