I. Concept 8.1: An organism’s metabolism transforms matter and energy,
subject to the laws of thermodynamics
a. _________________________________ is the totality of an organism’s chemical
reactions
i. Metabolism is an emergent property of life that arises from
interactions between molecules within the cell
b. A metabolic pathway begins with a specific molecule and ends with a
product
i. Each step is catalyzed by a specific
_________________________________
c. _________________________________ pathways release energy by breaking
down complex molecules into simpler compounds
i. _________________________________ respiration, the breakdown of
glucose in the presence of oxygen, is an example of a pathway
of catabolism
d. _________________________________ pathways consume energy to build
complex molecules from simpler ones
i. The synthesis of _________________________________ from amino acids
is an example of anabolism
e. _________________________________ is the study of how organisms manage
their energy resources
f. _________________________________ is the capacity to cause change
i. Energy exists in various forms, some of which can perform
work
1. Kinetic energy is energy associated with
_________________________________
2. Heat (thermal energy) is kinetic energy associated
with _________________________________ movement of atoms
or molecules
3. Potential energy is energy that matter possesses
because of its location or _________________________________
4. _________________________________ energy is potential energy
available for release in a chemical reaction
a. Energy can be converted from one form to
another
g. _________________________________ is the study of energy transformations
i. A closed system, such as that approximated by liquid in a
thermos, is isolated from its surroundings
ii. In an open system, energy and matter can be
_________________________________ between the system and its
surroundings
1. Organisms are _________________________________ systems
iii. The First Law of Thermodynamics
1. According to the first law of thermodynamics, the
energy of the universe is _________________________________:
2. Energy can be transferred and transformed, but it cannot
be created or destroyed
a. The first law is also called the principle of
conservation of energy
iv. The Second Law of Thermodynamics
1. During every energy transfer or transformation, some
energy is unusable, and is often lost as
_________________________________
2. According to the second law of thermodynamics:
a. Every energy transfer or transformation increases
the _________________________________ (disorder) of the
universe
h. Cells create ordered structures from less ordered materials
i. Organisms also replace ordered forms of matter and energy
with less ordered forms
ii. Energy flows into an ecosystem in the form of light and exits in
the form of heat
iii. The evolution of more complex organisms does not violate the
second law of thermodynamics
iv. Entropy (disorder) may _________________________________ in an
organism, but the universe’s total entropy
_________________________________
Lecture Questions 8.1 Metabolism, Energy, and Life
1. Explain the role of catabolic and anabolic pathways in cellular metabolism.
2. Explain the first and second laws of thermodynamics in your own words.
II. Concept 8.2: The free-energy change of a reaction tells us whether or not the
reaction occurs spontaneously
a. Biologists want to know which reactions occur
_________________________________ and which require input of energy
i. To do so, they need to determine energy changes that occur in
chemical reactions
b. A living system’s _________________________________ energy is energy that
can do work when temperature and pressure are uniform, as in a
living cell
i. Free-Energy Change, _________________________________
ii. The change in free energy (∆G) during a process is related to
the change in enthalpy, or change in total energy (∆H), change
in entropy (∆S), and temperature in Kelvin (T):
1. _________________________________
2. Only processes with a _________________________________ ∆G
are spontaneous
iii. Spontaneous processes can be harnessed to perform work
c. Free energy is a measure of a system’s instability, its tendency to
change to a more stable state
i. During a spontaneous change, free energy
_________________________________ and the stability of a system
_________________________________
ii. _________________________________ is a state of maximum stability
1. A process is spontaneous and can perform work only
when it is moving toward equilibrium
d. The concept of free energy can be applied to the chemistry of life’s
processes
i. There are 2 metabolic reaction types:
1. An _________________________________ reaction proceeds with
a net release of free energy and is spontaneous
2. An _________________________________ reaction absorbs
(stores) free energy from its surroundings and is
nonspontaneous
e. Reactions in a closed system eventually reach equilibrium and then do
no work
i. Cells are _________________________________ in equilibrium; they are
open systems experiencing a constant flow of materials
ii. A defining feature of life is that metabolism is never at
equilibrium
1. A catabolic pathway in a cell releases free energy in a
series of reactions
Lecture Questions 8.2 Free Energy
1. Write and define each component of the equation for free-energy change.
III. Concept 8.3: ATP powers cellular work by coupling exergonic reactions to
endergonic reactions
a. A cell does three main kinds of work:
i. Chemical
ii. _________________________________
iii. Mechanical
b. To do work, cells manage energy resources by energy
_________________________________, the use of an exergonic process to drive
an endergonic one
i. Most energy coupling in cells is mediated by
_________________________________
c. ATP (adenosine triphosphate) is the cell’s energy shuttle
i. ATP is composed of ribose (a sugar), adenine (a nitrogenous
base), and three phosphate groups
ii. The bonds between the phosphate groups of ATP’s tail can be
broken by hydrolysis
iii. Energy is released from ATP when the terminal phosphate
bond is broken
iv. This release of energy comes from the chemical change to a
state of lower free energy,
_________________________________ from the phosphate bonds
themselves
d. The three types of cellular work (mechanical, transport, and chemical)
are powered by the hydrolysis of ATP
i. ATP drives endergonic reactions by
_________________________________, transferring a phosphate group
to some other molecule, such as a reactant
1. The recipient molecule is now phosphorylated
ii. ATP is a renewable resource that is regenerated by addition of
a phosphate group to adenosine diphosphate (ADP)
1. The energy to phosphorylate ADP comes from
_________________________________ reactions in the cell
iii. The chemical potential energy temporarily stored in ATP
drives most cellular work
Lecture Questions 8.3 ATP Power
1. Explain how ATP performs cellular work.
IV. Concept 8.4: Enzymes speed up metabolic reactions by lowering energy
barriers
a. A _________________________________ is a chemical agent that speeds up a
reaction without being consumed by the reaction
b. An _________________________________ is a catalytic protein
i. Hydrolysis of sucrose by the enzyme
_________________________________ is an example of an enzymecatalyzed reaction
c. Every chemical reaction between molecules involves bond breaking
and bond forming
i. The initial energy needed to _________________________________ a
chemical reaction is called the free energy of activation, or
activation energy (EA)
ii. Activation energy is often supplied in the form of
_________________________________ from the surroundings
d. Enzymes catalyze reactions by lowering the EA barrier
i. Enzymes do not affect the change in free energy (∆G); instead,
they hasten reactions that would occur eventually
e. The reactant that an enzyme acts on is called the enzyme’s
_________________________________
i. The enzyme binds to its substrate, forming an enzymesubstrate complex
ii. The _________________________________ site is the region on the
enzyme where the substrate binds
iii. _________________________________ fit of a substrate brings chemical
groups of the active site into positions that enhance their
ability to catalyze the reaction
f. In an enzymatic reaction, the substrate binds to the active site of the
enzyme
i. The active site can lower an EA barrier by
1. Orienting substrates correctly
2. _________________________________ substrate bonds
3. Providing a favorable microenvironment
4. _________________________________ bonding to the substrate
g. An enzyme’s activity can be affected by
i. General environmental factors, such as
_________________________________ and pH
ii. Chemicals that specifically influence the enzyme
h. Effects of Temperature and pH
i. Each enzyme has an optimal temperature in which it can
function
ii. Each enzyme has an optimal pH in which it can function
i. _________________________________ are nonprotein enzyme helpers
i. Cofactors may be inorganic (such as a metal in ionic form) or
organic
ii. An organic cofactor is called a _________________________________
1. Coenzymes include _________________________________
j.
_________________________________ inhibitors bind to the active site of an
enzyme, competing with the substrate
k. _________________________________ inhibitors bind to another part of an
enzyme, causing the enzyme to change shape and making the active
site less effective
i. Examples of inhibitors include toxins, poisons, pesticides, and
antibiotics
8.4 Protein Enzymes Regulate Metabolic Pathways
1. Explain the induced-fit model of enzyme function.
2. Explain how substrate concentration affects the rate of an enzyme-catalyzed
reaction.
V. Concept 8.5: Regulation of enzyme activity helps control metabolism
a. Chemical chaos would result if a cell’s metabolic pathways were not
tightly regulated
i. A cell does this by switching on or off the genes that encode
specific enzymes or by regulating the activity of enzymes
b. _________________________________ regulation may either inhibit or
stimulate an enzyme’s activity
i. Allosteric regulation occurs when a regulatory molecule binds
to a protein at one site and affects the protein’s function at
another site
ii. Most allosterically regulated enzymes are made from
polypeptide subunits
c. Each enzyme has active and inactive forms
i. The binding of an activator stabilizes the
_________________________________ form of the enzyme
ii. The binding of an inhibitor stabilizes the
_________________________________ form of the enzyme
d. _________________________________ is a form of allosteric regulation that can
amplify enzyme activity
i. In cooperativity, binding by a substrate to one active site
stabilizes _________________________________ conformational changes
at all other subunits
e. Allosteric regulators are attractive drug candidates for enzyme
regulation (much more specific)
i. Inhibition of proteolytic enzymes called caspases may help
management of inappropriate inflammatory responses
f. In _________________________________ inhibition, the end product of a
metabolic pathway shuts down the pathway
i. Feedback inhibition prevents a cell from wasting chemical
resources by synthesizing more _________________________________
than is needed
g. Structures within the cell help bring order to metabolic pathways
i. Some enzymes act as structural components of membranes
1. In eukaryotic cells, some enzymes reside in specific
organelles; for example, enzymes for cellular
respiration are located in _________________________________
Lecture Questions 8.5 The Control of Metabolism
1. Describe how allosteric regulators may inhibit or stimulate the activity of an enzyme.