Biology – Kevin Dees
The Chemistry of LifeConcepts taken from chapters 2, 3 & 4
Biology – Kevin Dees
• Organisms are composed of matter• Anything that takes up space and has mass• Abiotic items are also composed of matter
• Matter is made up of elements• A substance that cannot be broken down into other
substances by chemical reactions• There are about 92 naturally occurring elements
– Oxygen, O– Carbon, C– Iron, Fe– Zinc, Zn– Etc…
Biology – Kevin Dees
Of the 92, naturally occurring elements, only 25 are known to be essential to life
• of these 25, only four (4) compose approx. 96% of living matter– Carbon, C– Oxygen, O– Hydrogen, H– Nitrogen, N
Biology – Kevin Dees
Trace elements
• Required by organisms in very small quantities
• Still very important despite their limited abundance– Fe, iron – required for oxygen transport– I, iodine – needed to produce a hormone in
the thyroid gland - goiter
Biology – Kevin Dees
Atoms
• The properties of elements depend on atoms
• Smallest unit of matter that retains the properties of an element
• Atoms are composed of subatomic particles
• Neutrons- no charge “neutral’• Electrons – negative charge• Proton – positive charge
Biology – Kevin Dees
Structure of atoms
• Nucleus– Protons– Neutrons
• Electrons orbit the nucleus
Biology – Kevin Dees
Atoms join to form molecules and compounds
• Two or more atoms join to form a molecule– i.e. H2 - hydrogen molecule
• A compound consists of two or more different atoms joining to form a molecule– i.e. H2 O – water molecule; also a compound
Biology – Kevin Dees
Chemical bonds hold atoms together in molecules and compounds
• Covalent bonds– Sharing of electrons by atoms– Very strong– Represented by dashed line in structural
formula• H-O-H
– May be single (one pair of electrons shared ) or double (2 pr. shared)
– May create polar molecules ( areas of charge)• H2O is polar
Biology – Kevin Dees
Water molecule – example of polar covalent bonding
Biology – Kevin Dees
• Ionic bonding – transfer (loss or gain) electrons
– Formation of ions – charged atom• Cation – positive charge – lost electron• Anion – negative charge – gained electron
– Bonds form due to attraction between anions and cations
– Very strong
Biology – Kevin Dees
• Hydrogen bonds– Very weak individually;
strength in numbers– Attractions between
partially positive H atoms and partially negative atoms
– Example: joins water molecules together
Biology – Kevin Dees
Fig. 2-UN2
Reactants Reaction Products
2 H2 O2 2 H2O
Biology – Kevin Dees
Water – special properties• Hydrogen bonding and polarity make
water very important to life’s processes
• Water is :Cohesive – hydrogen bonding holds
water molecules together
Biology – Kevin Dees
Water molecules pulled up the tissues of a plantor
creates surface tension on water’s surface
Biology – Kevin Dees
• Water is :–Able to absorb large quantities of
heat and only slightly change its own temperature – specific heat• Affect on climate – moderates coastal
climates• Insulation• Evaporative cooling – as water
absorbs energy and changes state (from liquid to gas), heat energy is taken away
Biology – Kevin Dees
• Water is:– Less dense as a solid than a liquid– “Ice floats”!!!!– This is important to water bodies
as they freeze in the winter. The ice floats and insulates the water beneath it!!!
Ice –stable crystals due to H bonds
Liquid water – H bonds break and reform
Biology – Kevin Dees
• Water is:– The universal solvent– The mixing of two or more substances is
known as a solution• The dissolving agent is the solvent• The substance dissolved is the solute
– Water dissolves polar or ionic compounds » Hydrophilic - water loving
– Water does not dissolve nonpolar compounds» Hydrophobic - water hating
Biology – Kevin Dees
• H2O H+ + OH-
• water hydrogen ion + hydroxide ion• These ions effect the pH (concentration of Hydrogen
ions)• pH scale:• Buffers - minimize change in hydrogen and hydroxide
ions
Water molecules may also dissociate – form ions
H+ > OH- = Acidic H+ < OH- = Basic
1470
Neu
tral
Biology – Kevin Dees
The importance of carbon• Water is the universal medium for life but all life
is made of chemical compounds that contain carbon
• These are known as organic compounds– Compounds that contain covalently bonded carbon– Inorganic compounds - non-organic (NaCl)– Hydrocarbons – organic molecules with only carbon
and hydrogen– Lots of stored energy!!!!!!– ATP (adenosine triphosphate) – energy currency of
the cell
Biology – Kevin Dees
Properties of organic molecules depend on the arrangement of the carbon skeleton and the
molecular attachments to that carbon skeleton
• Carbon skeleton
• Functional groups
• Properties – determine function