AP Test Biochemistry Review
Life requires ~25 chemical elements
 About 25 elements are essential for life

Four elements make up 96% of living
matter:
• carbon (C)
• oxygen (O)

• hydrogen (H)
• nitrogen (N)
Four elements make up most of
remaining 4%:
• phosphorus (P) • calcium (Ca)
• sulfur (S)
• potassium (K)
AP Biology
2005-2006
Ionic bonds
 Transfer of an electron
 Forms + & - ions
+ = cation
 – = anion

 Weak bond
AP Biology
 example:

salt = dissolves
easily in water
2005-2006
Covalent bonds
 Two atoms need an electron
 Share a pair of electrons
 Strong bond

both atoms holding onto the electrons
 Forms molecules
 example:

AP Biology
water = takes energy to separate
2005-2006
Polar covalent bonds
 Pair of electrons not shared equally by
2 atoms
 Water = O + H
oxygen has stronger
“attraction” for the
shared electrons than
hydrogen
 oxygen has higher
electronegativity

AP Biology
2005-2006
Polar covalent bonds
 2 hydrogens in the water molecule form
an angle
 Water molecule is polar
oxygen end is –
 hydrogen end is +

 Leads to many
interesting properties
of water….
AP Biology
2005-2006
Hydrogen bonds
 Positive H atom in
1 water molecule is
attracted to negative O
in another
 Can occur wherever an
-OH exists in a larger
molecule
 Weak bonds
AP Biology
2005-2006
Review Chapter 2
 Matter is made of atoms
 Life requires ~25 chemical elements
 Atomic structure determines behavior of an




element
Atoms combine by chemical bonding to form
molecules
Weak chemical bonds play important roles in
chemistry of life
A molecule’s biological function is related to its
shape
Chemical reactions make & break chemical bonds
AP Biology
2005-2006
Chemistry of water
 H2O molecules form H bonds with each
other
+ attracted to –
 creates a sticky
molecule

AP Biology
2004-2005
Cohesion
 H bonding between H2O creates
cohesion
water is “sticky”
 surface tension
 drinking straw
 Water bugs
 Water moves up a tree

AP Biology
2004-2005
Adhesion
 H2O molecules form H bonds with other
substances
meniscus
 water climbs up fiber

 ex. paper towel
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2004-2005
Water is the solvent of life
 H2O is a good solvent due to its polarity
polar H2O molecules surround + & – ions
 solvents dissolve solutes creating
aqueous solutions

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2004-2005
Hydrophilic
 Hydrophilic
substances have affinity for H2O
 Polar: they have a charge

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2004-2005
Hydrophobic
 Hydrophobic
substances do not have affinity for H2O
 Non-polar
 Oil, wax, fats

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fat (triglycerol)
2004-2005
Ice is less dense then liquid water
 Ice floats!
H bonds form a crystal with
loose structure
 Molecules are further apart and less
dense

AP Biology
2004-2005
Specific heat
 H2O has high specific heat

due to H bonding: it takes a lot of energy
to change the temperature of water
 H2O resists changes in temperature
takes a lot to heat it up
 takes a lot to cool it down

 H2O moderates temperatures on Earth
AP Biology
2004-2005
Evaporative cooling
 Organisms rely on
heat of vaporization
(energy required to
turn liquid to gas) to
remove heat
 As bonds are broken,
heat is released into
the environment
AP Biology
2004-2005
Water forms ions
 Hydrogen ion (H+) splits off from water to
leave a hydroxide ion (-OH)
H20 ----> H+ + -OH
 If concentration of 2 ions is equal,
water is neutral
 If [H+] > [-OH], water is acidic
 If [-OH] > [H+], water is basic
 pH scale = how acidic or basic a solution is
AP Biology
2004-2005
Chemistry of Life
 Organic chemistry is the study of
carbon compounds
 C atoms are versatile building blocks
4 electrons in outer shell
 4 stable covalent bonds

AP Biology
2003-2004
Isomers
 Molecules with same molecular formula
but different structures

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different chemical properties
2003-2004
How to build a polymer
 Condensation reaction
dehydration synthesis
 joins monomers by “taking” H2O out
 requires energy
& enzymes

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2005-2006
How to break down a polymer
 Hydrolysis

use H2O to break apart monomers
 reverse of condensation reaction
 H2O is split into H and OH
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2005-2006
Carbohydrates
Lipids
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Proteins
Nucleic Acids
2005-2006
Metabolism
 Metabolism is the sum of all chemical
reactions in your body.
 If a reactions breaks things down, it is
catabolic
 If a reaction builds things up, it is
anabolic
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Energy is released or
consumed
 In an exergonic reaction energy





is released.
When you break things down,
you release energy
All catabolic reactions are
exergonic
Cellular respiration is exergonic.
These are spontaneous
reactions
Delta G (a measure of free
energy) is negative
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Energy is released or
 consumed
In an endergonic reaction energy





is absorbed.
When you build things, you need
energy
All anabolic reactions are
endergonic
Photosynthesis is endergonic
These are non-spontaneous
reactions
Delta G is positive
AP Biology
Enzymes!
 Enzymes are proteins. They are
catalysts that speed up chemical
reactions by lowering the amount of
energy needed for those reactions to
start (activation energy)
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