Topic 1:Chemicals of life
1. Molecules and Atoms
2. Water
3. Carbon and other elements
1. Atoms and Molecules
1.1 Elements and Compounds
1.2 Elements of Life
1.3 Chemical and Physical Bonds
1.4 Importance of Carbon, Nitrogen, and
Water
Elements combine to
form compounds.
cannot be broken down to
other substances by
chemical reactions
Matter is made up of elements.
Organisms are composed of matter.
anything that has mass and
takes up space
Emergent Properties
+
Sodium
Chloride
Sodium Chloride
compounds have characteristics different from those of their elements
Essential Elements
(elements required by living organisms)
trace elements
• Fe, I, Cu, Mn, etc.
• required in minute (tiny) amounts
microelements
• Na, K, Ca, Mg, P, S, Cl
• 4% of living matter
macroelements
• C, H, O, N
• 96% of living matter
the properties of elements depend on the chemical
characteristics of their atoms
chemical characteristics of atoms depend on the arrangement of
electrons in electron shells (electron configuration)
Electronegativity
• the attraction of an atom for electrons from other atoms
• important property of elements of life
Bonds
Chemical
Bonds
Physical
Bonds
form between elements
form between molecules
Covalent
Ionic
Dipole
Interactions
Van der Waals
Chemical Bonds
Covalent Bonds
elements of similar electronegativity
share pairs of electrons
Ionic
Bonds
elements of very different
electronegativity transfer electrons,
creating ions (anions and cations)
The properties of a compound (solubility, melting point,
etc.) depend on the type of bonding involved.
Covalent bonds are the most important in biological
molecules because they allow for a variety of properties
H H
single covalent bond
O O
double covalent bond
N N
triple covalent bond
they can be single, double, or triple bonds
Covalent bonds can be classified as non-polar or polar
non-polar covalent
bonds
water
(elements of the same or almost the
same electronegativity)
polar covalent bonds
(elements of slightly different
electronegativity)
ethane
create dipoles - molecules with partial
negative (𝛿-) and positive (𝛿+) charges at
opposite ends
Physical Bonds
weak attractions between molecules (not the result of
chemical reactions)
There are two major types of Physical Bonds
Dipole Interactions
Attraction between opposite poles
of polar molecules (dipoles)
Van der Waals
Interactions
(aka London Dispersion Forces)
Caused by momentary asymmetric
distribution of moving electrons in large
non-polar molecules.
Hydrogen Bonds
–
+
H
Water
(H2O)
O
H
+
–
Ammonia
(NH3)
N
H
+
H
H
+
+
• the most important dipole
interaction in biology
• forms when a hydrogen atom
covalently bonded to one
electronegative atom is also
attracted to another
electronegative atom from a
different molecule
bonds determine the shape of the molecule
Shape of a Molecule
• determines the biological function
• Differently-shaped molecules have different functions
• similar shape molecules can mimic the function of another
molecule (morphine/endorphins)
• Carbon is the element most widely used in
biomolecules due to its special properties.
• Organisms can obtain carbon in two ways:
inorganic carbon (CO2)
autotrophs
organic carbon (glucose)
heterotrophs
• Nitrogen is also essential to living organisms,
making part of proteins and nucleic acids.
• Organisms can obtain nitrogen in two ways:
inorganic nitrogen (N2)
atmosphere – microorganisms, fungi
minerals – nitrates for plants
organic nitrogen
from other organisms
Water
• fundamental to life
• organisms are composed mostly of water (65% in humans, 99% in
jellyfish)
• most chemical reactions in organisms take place in water (wet
chemistry)