Chapter 8 Study Guide
Vocabulary:
Word Roots:
ana- = up
cata- = down
endo- = within
ex- = out
kinet- = movement
therm- = heat
Key Terms:
Activation energy: The amount of energy that reactants must absorb before a
chemical reaction will start
active site: the specific portion of an enzyme that attaches to the substrate by
means of weak chemical bonds.
Anabolic pathway: A metabolic pathway that synthesizes a complex molecule from
simpler compounds.
ATP (adenosine triphosphate): An adenine-containing nucleoside triphosphate that
releases free energy when its phosphate bonds are hydrolyzed. This energy is used
to drive endergonic reactions in cells.
Catabolic pathway: A metabolic pathway that releases energy by breaking down
complex molecules to simpler compounds.
Catalyst: A chemical agent that changes the rate of a reaction without being
consumed by the reaction.
Chemical energy: Energy stored in the chemical bonds of molecules; a form of
potential energy.
Competitive inhibitor: A substance that reduces the activity of an enzyme by
entering the active site in place of the substrate whose structure it mimics.
Endergonic reaction: A non-spontaneous chemical reaction, in which free energy is
absorbed from the surroundings.
1
Energy: The capacity to do work (to move matter against an opposing force)
Entropy: A quantitative measure of disorder or randomness
Enzyme: A protein serving as a catalyst, a chemical agent that changes the rate of a
reaction without being consumed by the reaction.
Enzyme-substrate complex: A temporary complex formed when an enzyme binds to
its substrate molecule(s).
Exergonic reaction: A spontaneous chemical reaction, in which there is a net release
of free energy.
First law of thermodynamics: The principle of conservation of energy. Energy can
be transferred and transformed, but it cannot be created or destroyed.
Free energy: The portion of a system’s energy that can perform work
Heat: The total amount of kinetic energy due to molecular motion in a body of
matter. Heat is energy in its most random form.
Induced fit: The change in shape of the active site of an enzyme so that it binds
more snugly to the substrate, induced by entry of the substrate.
Kinetic energy: The energy of motion
Metabolic pathway: A series of chemical reactions that either builds a complex
molecule (anabolic pathway) or breaks down a complex molecule into simpler
compounds (catabolic pathway).
Metabolism: The totality of an organism’s chemical reactions, consisting of catabolic
and anabolic pathways.
Non-competitive inhibitor: A substance that reduces the activity of an enzyme by
binding to a location remote from the active site, changing its conformation so that it
no longer binds to the substrate.
Phosphorylated: Referring to a molecule that has been the recipient of a phosphate
group.
Potential energy: The energy stored by matter as a result of its location or spatial
arrangement.
Second law of thermodynamics: The principle whereby every energy transfer or
transformation increases the entropy of the universe.
2
Substrate: The reactant on which an enzyme works.
Thermodynamics: The study of energy transformations that occur in a collection of
matter.
Chapter 8 Important Points:
Metabolism:
 The cell has countless chemical reactions occurring at all times, these
reactions make up our metabolism.
 All chemical reactions involve the breaking of initial bonds between atoms in
reactant molecules and the forming of new bonds between the same atoms in
different arrangements to make product molecules.
 Some chemical reactions require energy to create the new products and are
therefore called endergonic. Reactions that release energy are called
exergonic. In general, endergonic reactions are non-spontaneous and part of
anabolic pathways in which larger macromolecules are made from smaller
molecules.
 Exergonic reactions are spontaneous and part of catabolic pathways in which
larger molecules are broken into smaller ones.
 Free energy (G) is a measure of how much energy is available to do work. If
a molecule has a high amount of free energy compared to another molecule,
the one with the higher free energy has more potential energy stored in its
bonds.
 Endergonic reactions have reactant molecules with less free energy than the
products therefore the change in free energy is positive from the beginning to
end of the reaction.
 Exergonic reactions have reactant molecules with more free energy than the
products therefore the change in free energy is negative from the beginning
to end of the reaction.
 Cell respiration is a catabolic pathway and photosynthesis is an anabolic
pathway.
 Two Laws of Thermodynamics dictate the change of energy from one form to
another.
o First Law (Law of Conservation of Energy) states that the amount or
quantity of energy does not change so energy is not created or
destroyed, just changed from one form to another.
 Ex. The energy in the chemical bonds of potential energy in
food molecules is converted to ATP bonds that can cause the
contraction of a muscle which is a form of kinetic energy.
o Second Law states that when energy changes from one form to
another, the quality of energy decreases as entropy (which is the
amount of disorder) increases. This tells us that energy conversion is
NOT 100% efficient since heat energy, which is a less organized form
of energy, is always generated by every energy transformation.
3

For example, only about 40% of the chemical energy stored in
a glucose molecule can be accounted for in the ATP molecules
that are generated during cell respiration. The rest turns into
heat energy.
ATP:
 ATP stands for adenosine triphosphate, and it is a common molecule used by
the cell to provide energy for endergonic reactions and events.
 The energy in ATP is stored between the 3 phosphate groups which all have a
negative charge so making them bond together takes a great deal of energy
(like compressing a spring)
 Each ATP molecule has a relatively small amount of energy but will be
sufficient for an individual energetic job of the cell.
 ATP powers cellular jobs by phosphorylating other molecules which means
the terminal (last) phosphate group is broken off from ATP by hydrolysis and
that the free phosphate group temporarily bonds to another molecule.
 Once the terminal phosphate group is released, ADP (adenosine
diphosphate) is left, waiting to be recycled back into ATP by adding a free,
inorganic phosphate group.
Enzymes:
 Enzymes are catalytic proteins which means they have all the properties of
proteins but serve specifically as catalysts for chemical reactions so they help
chemical reactions occur without being used up in the reactions themselves.
o This means the atoms in an enzyme are not incorporated into the
products of the reactions and that a given enzyme can be used over
and over.
 Enzymes allow reactions to occur easier because they lower the amount of
activation energy needed for reactant molecules’ bonds to be broken.
 Typical enzyme names can end in “-ase”
 A reactant in an enzymatically controlled reaction is called a substrate and
each enzyme has a match with a particular substrate
 Substrates bind specifically with the area on an enzyme called the active site
o Induced fit refers to a tight association when the proper substrate
binds with the correct active site forming an enzyme-substrate
complex
 Each enzyme works best (optimally) in a narrow range of environmental
conditions such as temperature or pH. If varying too far from this ideal, the
conformation of the enzyme will be changed and the active site will not bind
as well to the substrate, reducing the enzyme’s activity
 When all active sites are bound to substrate, the reaction has reached
saturation and the only way to overcome it is to add more enzyme
 Competitive inhibitors are molecules that are NOT the proper substrate but
bind to the active site of enzymes, thus blocking the real substrate and
slowing down the reaction.
4

Non-competitive inhibitors also slow down the reaction but bind to a different
area of the enzyme (not the active site) but cause the active site to change so
that the real substrate can not bind.
5