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CHAPTER 2
THE CHEMISTRY OF CELLS
SO WHAT DOES CHEMISTRY
HAVE TO DO WITH
BIOLOGY????
• Thomas Eisner
pioneered chemical
ecology
– the study of the
chemical language of
nature
• He studies how insects
communicate via
chemical messages
BETTER LIVING THROUGH
CHEMISTRY……..
• Rattlebox moths release a
chemical that spiders don’t
like
• This spider caught a
rattlebox moth and then let
it go
ATOMS AND MOLECULES
• Everything an organism is and does depends on
chemistry
• Chemistry is in turn dependent on the
arrangement of atoms in molecules
• In order to understand the whole, biologists
study the parts.
Molecules and ecosystems are
at opposite ends of the
biological hierarchy
–Each level of organization in
the biological hierarchy builds
on the one below it
–At each level, new properties
emerge…in other words-the
higher up the ladder..the more
complicated
A biological hierarchy
D. Organ: Flight muscle of a
moth
•
•
•
•
•
•
C. Cell and tissue: Muscle
cell within muscle tissue
Myofibril (organelle
B. Organelle:
Myofibril (found only
in muscle cells)
Actin
A. Molecule: Actin
Myosin
Atom
Organ
Tissue
Cell
Organelle
Molecule
Atom
LIFE REQUIRES ABOUT 25
CHEMICAL ELEMENTS
• A chemical element is a substance that
cannot be broken down to other substances
by ordinary chemical means
• About 25 different chemical elements are
essential to life
• Carbon,
hydrogen,
oxygen, and
nitrogen make
up the bulk of
living matter,
but there are
other elements
necessary for
life
IODINE IS A REQUIREMENT
• Goiters are caused by iodine deficiency
ELEMENTS CAN COMBINE
TO FORM COMPOUNDS
• Chemical elements combine in fixed ratios to form
compounds
• Example: sodium + chlorine  sodium chloride
Atoms consist of protons,
neutrons, and electrons
• The smallest particle of an element is an
atom
• Different elements have different types of
atoms
An atom is made up of protons
and neutrons located in a central
nucleus
• The nucleus is surrounded by electrons
Protons
Neutrons
Electrons
A. Helium atom
Nucleus
Each atom is held together by
attractions between the positively
charged protons and negatively
charged electrons
• Neutrons are electrically neutral
B. Carbon atom
6
6
6
Protons
Neutrons
Electrons
Nucleus
Atoms of each element are
distinguished by a specific
number of protons
– The number of neutrons may vary
– Variant forms of an element are called isotopes
– Some isotopes are radioactive
Connection: Radioactive isotopes
can help or harm us
• Radioactive isotopes can be useful tracers for studying
biological processes
• PET scanners use radioactive isotopes to create anatomical
images
Electron arrangement determines
the chemical properties of an
atom
• Electrons are arranged in shells
– The outermost shell determines the chemical
properties of an atom
– In most atoms, a full outer shell holds eight
electrons
Atoms whose shells are not full
tend to interact with other atoms
and gain, lose, or share electrons
Outermost electron shell (can
hold 8 electrons)
Electron
First electron shell (can hold 2 electrons)
HYDROGEN (H)
Atomic number = 1
CARBON (C)
Atomic number = 6
NITROGEN (N)
Atomic number = 7
OXYGEN (O)
Atomic number = 8
Ionic bonds are attractions
between ions of opposite charge
Na
Sodium atom
Cl
Chlorine atom
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
• When atoms gain or lose electrons, charged
atoms called ions are created
– An electrical attraction between ions with opposite
charges results in an ionic bond
Sodium and chloride ions bond to
form sodium chloride, common
table salt
Na+
Cl–
Covalent bonds, the sharing of
electrons, join atoms into
molecules
• Some atoms share outer shell electrons
with other atoms, forming covalent bonds
– Atoms joined together by covalent bonds form
molecules
• Molecules can
be represented
in many ways