Molecules of Life:
• Element: A substance that cannot be broken down to other substances by
• Atom: The smallest unit of matter that still retains the properties of an
• Atoms of some elements react with other atoms to form a molecule in order to
fulfill requirements to maintain chemical stability. Molecule: Composed of
two or more atoms of the same element.
• Compound: A molecule composed of two or more different elements (in a
fixed ratio); a compound has characteristics different from those of its
• Ionic Bonds: Atoms take electrons away from their bonding partners,
fulfilling the need for the optimum number of electrons in their outer shells.
o Ionic Compounds (or salts): Formed by ionic bonds
• Ion: A charged atom (or charged molecule)
o Cation: positively charged
o Anion: negatively charged
• Covalent Bond: The sharing of one or more pair(s) of valence shell (outer
shell) electrons by two atoms to achieve the number required for stability.
o Single Bond: The sharing of one or more pair of valence electrons
o Double Bond: The sharing of two pairs of valence electrons
• Structural Formula: Used to represent bonding between atoms (i.e. H–H)
o Molecular Formula: Abbreviation of structural formula (i.e. H2,
• Nonpolar Covalent Bond: Formed when atoms share an electron equally.
• Electronegativity: A measure of an atom’s attraction for the electrons in a
• Hydrogen Bonds:
o Polar covalent bonds
o The electrons end up being a part of the larger atom rather than being
shared. The larger atom ends up having a negative charge and the
smaller one ends up being positive: the atoms have partial electrical
A polar covalent bond forms because the atoms end up being
attracted to each other due to their opposite partial electrical
• HBonds (polar covalent bonds):
o Water is a polar molecule: The oxygen end is more electronegative, the
hydrogen ends are more electropositive. The water molecules can thus
bond to each other as well
o The polarity and thus ability to form Hbonds give water molecules
certain properties that are most important for life.
• Water and Its Important Properties:
o Water Molecules Show Cohesion and Adhesion Cohesion: Water molecules can bond to each other
Adhesion: Water molecules can bond to other polar molecules
(i.e. cellulose in plant cell walls)
Main force of upward movement: transpirational pull:
• Generally, the outside air has less water vapor than the
inside of leaf cells. Therefore, water in the spaces of
mesophyll diffuses out of the stomata: transpiration.
Significance: Water molecules cling to each other and the cell
walls to ‘climb’ through xylem and to top of tree (important in
• Evaporative tension at top pulls the chain of water
molecules up. IMPORTANT FOR PLANT
o Water Can Form Three Physical States
Ice: All possible HBonds (4/water molecule) are formed
Water: A moderate number of Hbonds are formed
Steam: Nearly no Hbonds are formed
• Heat energy needs to be applied to water or ice to
break the Hbonds
• Heat energy needs to be removed from steam so H
bonds can reform
Significance: homeostasis of body temperature, maintaining
life, rain cycles
o Water Expands When It Forms Ice
Ice is lighter than water. The molecules are spaced far apart: fewer
molecules per unit area.
Significance: Liquid water underneath the frozen surfaces can
sustain life. If ice sank, all bodies of water would eventually freeze
solid, making life on Earth impossible.
o Water Has High Solubility: It is The Solvent of Life
Water is a versatile solvent or a universal solvent
Sugars, salts dissolve in it and form uniform solutions.
Large proteins disperse in it and form suspensions.
Hydrophilic Substance: A substance that has affinity for water.
• can dissolve in water, not completely dissolve but ‘get wet’:
form Hbonds with water, or its molecules separate from
each other and form a uniform suspension in water
Hydrophobic Substance: waterrepelling
Significance: Water being a potent solvent is the basis of
biological solutions: cytoplasm of all cells, blood, plant sap, food
digestion and absorption, fluids in the body
Salts and simple sugars dissolve in water easily
• When salt is dissolved in water, each ion is surrounded by a
sphere of water molecules: called a shell of hydration Large polar molecules such as proteins can dissolve in water if
they have ionic and polar regions
• Important: Unlike salt, the proteins do not completely fall
apart into amino acids or ions. A whole protein molecule is
surrounded by water so it cannot attach to another protein:
forms a uniform suspension in water. The proteins retain
their biological activity in solution; an example of ‘getting
o The MillerUrey Experiment
Found evidence of synthesis of organic molecules from inorganic
o Dehydration Vs Hydrolysis:
o Dehydration or Condensation:
Removal of H2O molecules from reacting molecules: joins
the units together, forms longer chains: CAUSES
Addition of H2O molecules to the polymer: breaks the
bonds between monomers: breaks the chains into smaller
units: CAUSES DEPOLYMERISATION.
o Catabolic Reactions: release energy
o Anabolic Reactions: require energy
o 4 Macromolecules
*Carbohydrates have many OH molecules and ringed
Include sugars and the polymers of sugars.
All sugars form ring structures in water: do not stay as chains in
Monosaccharides: single units, simple sugars (i.e. glucose)
• Classified by:
o The number of carbons in the carbon skeleton
o The locat