Biology 1401
Dr. Wedig
What should I learn from
Chapter 6?
 Define vocabulary/terms related to energy utilization
and transformation.
 Explain the different sources of energy available to
living organisms.
 Understand the process of energy transformation, and
associated energy losses.
 Explain how enzymes function, and factors affecting
rate of chemical reactions.
 Identify mechanisms involved in controlling chemical
reactions (inhibition, activation, homeostasis)
Bioenergetics
 Study of how
organisms manage
their energy resources
 Energy: fundamental
to all metabolic
processes
 Energy: capacity to
do work
Forms of Energy
 Kinetic energy: energy of motion
 Potential energy: stored energy
 Chemical energy: a form of potential energy
 energy is stored as bond energy
 Energy transformation: chemical energy can
be transformed to kinetic energy
 Thermal Energy: heat
Thermodynamics
• Study of energy transformations
• Laws of thermodynamics
– Law of Conservation of Energy
• Energy can be transferred and transformed, but can be
neither created nor destroyed
• Transfer or transformation of energy is not 100% efficient
– some is released as heat
– heat: energy of random molecular motion; most systems can
not harvest this form of energy to do work
– Law of Entropy
Gasoline has potential
energy in its chemical
bonds
Car converts the
chemical energy of
gasoline to kinetic
energy
Free
Energy
 Portion of a systems
energy which can
perform work when
temperature is uniform
throughout the system
 Spontaneous reaction
 can occur without outside
help
 increases stability of the
system
 can be harnessed to do
work
Law of Entropy
 Every transfer or transformation of energy makes the
universe more disordered
 Entropy: quantitative measure of disorder
Life requires constant energy input
 Energy intake enables living systems to remain
ordered
 Anything which interferes with energy intake alters
ordered state (disease, injury)
 Transfer of energy in living systems is 30-40% efficient
 Complex organic molecules have great potential
energy
Types of Work Done by Cell
• Mechanical work
– contraction of muscle cells
– beating of cilia
– movement of
chromosomes during cell
division
• Transport work
– pumping substances across
membrane
• Chemical work
– anabolic processes
Coupled Reactions
 Part of a chain of events
 Exergonic reactions are coupled with endergonic
reactions
 ATP hydrolysis (exergonic) is used to phosphorylate
glucose (endergonic)
Enzymes
 Proteins that serve as catalysts for chemical reactions
taking place within living systems.
 Usually end with the suffix –ase
 Speeds up rate of reaction without being altered by the
reaction
 Mechanism of Action:  activation energy
 Does not change G
Activation Energy (EA)
 Initial investment of energy required for a reaction to
proceed
 Bonds of reactants break only when molecules have
absorbed sufficient energy to become unstable
 Transition state: unstable form of molecule
 Heat:  reaction rate by  rate of molecular motion
Active
Site
 Region of enzyme that recognizes and binds substrate
 Enzymes are substrate-specific
 Specificity is based on three-dimensional shape
(secondary, tertiary, quaternary structure)
 Only a few amino acids make up the active site
(responsible for substrate specificity); rest of protein
provides the framework that reinforces the configuration
of the active site.
Microenvironments
 Created by side chains of the amino acids at the active
site
 Acidic conditions: transfer H+ to the substrate
 Basic: take H+ from the substrate
 May be brief covalent bond formed between enzyme
and substrate to facilitate catalysis
Models of Enzyme Function
 Involve formation of an enzyme-substrate complex
 Lock-and-key
 Active site is complementary to substrate (shape and
functional groups)
 Induced fit
Induced Fit
 As substrate enters active site, it induces the enzyme to
slightly change shape
 Enzyme accommodates to substrate to bring chemical
groups of active site into position to interact with
substrate and enhance the ability of the enzyme to
catalyze the reaction
Hexokinase and
Glucose
Enzyme-Substrate Complex
 Substrate is held in place by ionic bonds, H bonds, and
hydrophobic interactions
 A few amino acids dictate associations between
enzyme and substrate
 Interactions between enzyme and substrate stabilize
the transition state, thereby decreasing EA
Chemical Energy and Life
 Exergonic reaction: net
release of energy
 -G (change in free
energy)
 characteristic of
catabolic reactions
 Endergonic reaction:
absorbs free energy
from its surroundings
 +G
 characteristic of anabolic
reactions
 G = Gfinal-Gstarting
Redox Reactions
 Involve a transer of one or more electrons from one
reactant to another
 reduction: gain of electrons (GER)
 oxidation: loss of electrons (LEO)
 Reducing agent: electron donor
 Oxidizing agent: electron acceptor
 Electronegativity: affinity for electrons
Redox Reactions
The Formation of Formaldehyde: A Redox Reaction
Carbohydrates in Redox Reactions
• C-H bonds store
energy
• Carbohydrates can
act as electron donors
in redox reactions
– Produce energy in
the form of ATP
Factors Affecting Reaction Rate
• Enzyme Concentration
–  enzyme concentration 
reaction rate
– If enzyme concentration
exceeds substrate
concentration, adding more
enzyme will not  reaction
rate
• Substrate Concentration
• Temperature
• pH
Substrate Concentration
  substrate concentration  reaction rate until
substrate concentration exceeds enzyme concentration
 Saturation: point at which all enzyme molecules are
occupied
Temperature
 Optimal temperature: fastest rate of reaction
 Reaction rate  as temperature  up to optimum
 Temperature optimum of most human enzymes is
between 35 and 40 ° C
 Denaturation: destruction of H bonds due to excessive
temperature
 Destroys secondary, tertiary, quaternary structure
  enzyme activity
pH Optimum
 pH at which enzyme functions optimally
 Most enzymes: 6-8
 Pepsin: 2
 Trypsin: 9
Cofactors
 Nonprotein components required by an enzyme for its
activity
 Inorganic/minerals
 Zn, Fe, Cu
 Organic/vitamins
Control of Enzyme Activity
 Competitive Inhibition
 Allosteric Regulation
 Noncompetitive Inhibition
 Allosteric Activation
 Cooperativity
 Metabolic Control
Noncompetitive Inhibitors
 Bind to enzyme at allosteric site
 Allosteric site: binding site separate from active site
 Binding of allosteric inhibitor changes the shape of
enzyme and prevents it from binding substrate
 May be reversible or irreversible
 Can not be overcome by adding substrate
Noncompetitive Inhibitors are also known as
allosteric inhibitors. They bind to a site
distant from or other than the active site.
Competitive Inhibitors
 Bind to Active site
 Look like substrate; compete with substrate for active
site
 Inhibition is reversible and can be overcome by adding
substrate
 Penicillin blocks a bacterial enzyme that is involved in
synthesizing the cell wall
Competitive Inhibition: a portion of the
inhibitor molecule looks like the substrate,
and is recognized by the active site.
Allosteric Activation
 An enzyme is inactive until the activator molecule
binds to allosteric site
 Activator: stabilizes active site (active form of the
enzyme)
 PFK and ATP/ADP levels
Allosteric Regulation
Allosteric Proteins often fluctuate between
inactive and active forms.
Allosteric activators and inhibitors
Cooperativity
 Amplifies response
 One substrate molecule primes an enzyme to accept
additional substrate molecules
 Hemoglobin and binding O2
Metabolic Control
 Each metabolic pathway (series of reactions that
functions to convert a reactant(s) to an endproduct(s)
is closely regulated by controlling enzyme activity
 Allosteric regulation
 PFK and ATP/ADP levels
 Feedback Inhibition: end-product of pathway feeds
back and inhibits a regulatory enzyme
 Threonine isoleucine
What did I learn from Chapter
6?
 Cells obtain energy needed to maintain life from
chemical energy.
 These cells transform chemical bond energy to energy
in the form of ATP; in the process of transformation,
energy is lost as heat.
 Some important elements to energy extraction and
ATP production by cells include:
 Enzyme function and factors affecting enzyme activity
 Feedback mechanisms, inhibitors, activators, coupled
reactions