The Chemistry
of Life
Ch. 4.1-4.3
Recall: Levels of
Organization
Biology Depends on Chemistry
• In our biosphere, everything is made of atoms
• Through the interaction of chemicals we can better
understand our biosphere
• Basic unit of matter
• Protons
Atoms
o (+) charge
o In nucleus
• Neutrons
o (0) charge
o In nucleus
• Electrons
o (-) charge
o Around nucleus at varying energy levels
Molecules
• 2 or more atoms held
together by chemical
bonds
• Importance to
biology:
macromolecules
make up cells and
cellular components
Chemical Bonds: Ionic
• Electrons transferred
from one atom to
another
• Ex: NaCl (salt)
• Importance to biology:
many salts are made
this way (homeostatic
balance)
Chemical Bonds: Covalent
• Electrons are shared between atoms
o Ex: CO2
• Importance to biology: carbon compounds,
water
Chemical Bonds: Hydrogen
• Weak bond formed from
by the attraction of two
electronegative molecules
o Slightly positive, slightly negative
ends
• Importance to biology:
critical to water’s
properties, holds DNA
together
Chemical Reactions
• Synthesis
o Make a compound
o Ex: Photosynthesis
• Decomposition
o Break down a compound
o Ex: Cellular Respiration
• Both reactions important to
biology: metabolism