Atoms,
Molecules and Life
BIO
101
Dr.
Daley
Elements
Substances which cannot be broken
down or decomposed into simpler substances by chemical reactions
Living organisms
Over 90% of most living organisms
is composed of
Carbon, hydrogen and oxygen
Chemical Symbol
One or two letter designation that
stands for the English or Latin name
H - hydrogen
O - oxygen
C - carbon
Cl -
chlorine
K - potassium
Na - sodium
Atom
Smallest unit of
an element.
Most basic unit
which reacts.
Atom
Subunits
Central nucleus
Protons& Neutrons
Orbiting the nucleus are
Electrons
Atom
Charge
Protons ----- +1
Neutrons ---- 0
Electrons --- -1
Atom
# of protons is unique
Atomic number (Z)
Electron Shells in Atoms
Energy Capture and Release
Life depends on the ability of
electrons to capture and release energy
Chemical Properties
Depends upon the number of
electrons in the outer most shell or orbit of the nucleus
Carbon
6 - Neutrons
6 - Protons
6 - Electrons
2 - innermost
orbit
4 - outermost
orbit
Molecule
New chemical unit formed by the
reaction (combination) of atoms
Compound
A substance whose molecules are
composed of two or more different atoms
Octet Rule
Atoms react with one another to
achieve 8 electrons in the outer most orbit (shell)
Hydrogen is an exception - 0nly 2
electrons at most in its one shell
An atom will not react if its outer
most orbit is completely full
Ionic Bonds
Transfer of electrons from one atom
to another to from a molecule
Atoms involved are called ions
Sodium Chloride
Covalent Bonds
Chemical
bonds where atoms share electrons
Most
biological molecules utilize covalent bonds - more stable than ionic bonds in a
water environment
Water
Covalently bonded together
Polar molecule
Free Radicals
Many
reactions that occur in cells give rise to molecules that have atoms (often
oxygen atoms) with one or more unpaired electrons in their outer shells -
called free radicals
These
react readily with nearby molecules capturing electrons to fill their outer
orbits
But
when a free radical steals an electron it creates another new free radical and
thus begins a chain reaction that can lead to the destruction of
biological molecules- this happens in heart disease and nervous disorders such
as AlzheimerÕs.
Free
radical may even damage DNA and cause cancer
Antioxidants (e.g. vitamin C & E) react with free radical and render
them harmless
Hydrogen Bonds
Electrostatic attraction between a
partially positively charged hydrogen and another negatively charged atom such
as oxygen in water
Hydrogen Bonding
Water and Ions
Acids
Acids- Molecules which dissociate
in water releasing hydrogen ions.
Bases
Molecules that
take up hydrogen atoms or dissociate in water releasing hydroxide ions.
pH
The H+ concentration is
usually expressed in pH units
pH scale
runs from 0 to 14
Pure water - 10-7 M - pH
7
A solution with 10 times more H+
ions - pH 6
Buffers
Chemicals or combinations of
chemicals that take up excess H+ or OH-to keep pH
constant