INTRODUCTION TO
METABOLISM.
Chapter 8
Metabolism, Energy, and Life
Objectives
• Explain the role of catabolic and anabolic pathways in
cell metabolism
• Distinguish between kinetic and potential energy
• Distinguish between open and closed systems
• Explain the first and second Laws of
Thermodynamics
• Distinguish between entropy and enthalpy
• Understand the Gibbs equation for free energy
change
• Understand how “usable” energy changes with
changes in enthalpy, entropy, and temperature
• Understand the usefulness of free energy
How to Read a Chemical Equation
• A chemical reaction starts with reactants and finishes with
products:
C6H1206 + 6O2  6CO2 +6H20 + ENERGY
reactant
product
6CO2 +6H20 + light  C6H1206 + 6O2
• Disturbing either the concentration or the energy of the system
alters the chemical equilibrium. Living things NEVER let
their reactions go to equilibrium
Metabolism
• The sum of all the chemical
processes occurring in an
organism at one time
• Concerned with the
management of material
and energy resources
within the cell
• Catabolic pathways
• Anabolic pathways
Catabolic Pathways
• Pathways that release energy
by breaking down complex
molecules into simpler
compounds
• Cellular respiration
• C6H1206 + 6O26CO2 +6H20 + ENERGY
Anabolic Pathways
• Pathways that consume
energy to build larger,
complicated molecules
from simpler ones
• Polymerization
• Photosynthesis
6CO2 +6H20 + light  C6H1206 + 6O2
Bioenergetics
• Study of how organisms manage their energy
resources
• Energy is the capacity to do work, to move
matter
– Kinetic energy: energy that is in motion
– Potential energy: stored energy based on location
or structure
• The rearrangement of atoms in molecules may
result in the potential energy of the molecule
being converted into kinetic energy
• Kinetic energy: energy of motion; all atoms
exhibit kinetic energy as all molecules are in
motion
http://galileo.phys.virginia.edu/classes/109N/more_stuff/Applets/brownian/brownian.html
• Potential energy: amount of energy
stored as a result of position or location
Energy Laws
Laws of Thermodynamics
• The terms open or closed systems refer to
whether or not energy can be transferred
between the system and its surroundings
(can energy be imported or exported)
• First Law of Thermodynamics: Energy can
neither be created nor destroyed, only
transformed from one type to another
• Second Law of Thermodynamics: Each
energy transformation results in less usable
(ordered) energy
Free Energy
G=H-TS
Free energy (G) is the portion of system energy
that can do work under uniform temperature
• Enthalpy or work
total energy is a
measure of all the
energy in a system
• Symbolically
represented as “H”
• Entropy is a
measure of
randomness
(disorder)
• Symbolically
represented as “S”
Temperature (T) is measured in K
G
• The higher the G the more unstable the system
• A change in free energy can occur with metabolism
– Exergonic: reactions that lose energy; -G
– Endergonic: reactions that gain energy; + G
– Metabolic reactions are often coupled where an exergonic reaction
fuels an endergonic reaction
• When G = 0 no work can be done
• When reactions go to equilibrium, G = 0
(therefore metabolic reactions do not usually reach an
equilibrium)
• Energy needed for Mechanical, Chemical, and Transport
workings of the cell
Objectives
• Explain the role of ATP in the cell
• Describe ATP’s composition and how it performs cellular
work
• Explain the importance of chemical disequilibrium
• Understand the energy profile of a reaction including:
activation energy, free energy change, & transition state
• Describe the role and mechanisms of enzymes
• Explain how enzyme activity can be controlled by
environmental factors, cofactors, enzyme inhibitors, and
allosteric regulators
• Distinguish between allosteric activation and
cooperativity
• Explain how metabolic pathways are regulated
ATP
• Energy molecule used
to couple exergonic
reactions to endergonic
• Nucleotide with three
phosphate groups
attached to the ribose
sugar
• ATP has a high G
ATP
• Energy is released from ATP through the loss of
phosphate groups
• Catabolic reaction resulting from hydrolysis
producing ADP + Pi (inorganic Phosphate) +
energy (G = -7.3Kcal/mol in the lab,
-13Kcal/mol in the cell)
How ATP works
• Hydrolysis of ATP produces
inorganic phosphate that is
attached to a molecule
involved in an endergonic
process
• Phosphorylation is the process
of ATP transferring phosphate
to a molecule
• Results in a phosphorylated
intermediate that can complete
the intended reaction
Regeneration of ATP
• ATP loses energy when it phosphorylates an
intermediate molecule of an endergonic reaction.
ATP becomes ADP
• Regeneration of ATP occurs when inorganic
phosphate (Pi) is bound to ADP utilizing energy
supplied by a catabolic reaction
How Do We Maximize Cellular
Efficiency?
• Use of ATP
– ATP is a good energy source because:
• It can participate in a many different kinds of reactions
within the cell
• Usually is directly involved in reactions
• Little wasted energy during phosphorylation of an
intermediate
• Use of enzymes
– Decrease randomness of reactions
• Regulation of enzymes and, thus, reactions
Enzymes
• Proteins that assist in chemical reactions may be
enzymes
– Specific because of conformational shape
• Enzymes are catalysts
– Catalyst: chemical that changes the rate of a reaction
without being consumed
– Recycled (used multiple times)
• Enzymes reduce the activation energy of a
reaction
– Amount of energy that must be added to get a reaction
to proceed
Activation Energy
• EA= Activation energy
• EA is usually supplied
by heat
• Reactants absorb heat
increasing G making
the reactants unstable
so they react
•
How
Enzymes
Work
Enzymes are substrate specific
– Substrate: any molecule to which
an enzyme will bind
• Although an enzyme can be a large
protein, only a specific region of the
enzyme interacts with the substrate
– Active Site: region of enzyme that
“reacts” to substrate
• As enzyme and substrate bind, the
enzyme shape is modified to better
fit the substrate
– Induced fit occurs as a result of the
enzyme substrate complex
Enzyme Activity
• The rate of an enzyme
catalyzed reaction is influenced
by 1) concentration of the
substrate or 2) enzyme
concentration
• Some enzymes utilize 3)
inorganic or 4) organic
molecules as helpers
– Cofactor: inorganic molecule
(mineral)
– Coenzyme: organic nonprotein molecule (vitamin)
Enzyme activity
• The rate at which an
enzyme can function is
dependant on several
physical factors
including:
– 5) Temperature
– 6) pH
• Why?
Enzyme Regulation
• Enzyme activity may be reduced
by molecules attaching to the
enzyme.
• Inhibition may occur at two
different locations
– competitive inhibition: inhibitor
mimics molecule that attaches to
active site
– noncompetitive inhibition at an
allosteric site: inhibitor binds to
enzyme away from the active site
resulting in modification of active
site
Control of Metabolism
• Allosteric Regulation: enzyme function may
be stimulated or inhibited by attachment of
molecules to an allosteric site
• Feedback Inhibition: end product of
metabolic pathway may serve as allosteric
inhibitor
• Cooperativity: single substrate molecule
primes multiple active sites increasing
activity