Download Define the term “energy” and distinguish between g potential and

Module 2D - Energy and Metabolism
Objective # 19
All living organisms require energy
for survival. In this module we will
examine some general principles
about chemical reactions and
energy usage within cells.
Define the term “energy”
and distinguish
g
between
potential and kinetic energy.
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Objective 19
Objective 19
„ Energy
is the ability to cause change.
Any change in the universe requires
energy. Energy comes in 2 forms:
¾ Potential energy
g is stored energy.
g No
change is currently taking place
¾ Kinetic energy is currently causing
change. This always involves some
type of motion.
Two Forms of Energy
Potential energy
Kinetic energy
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Objective # 20
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Objective 20
„ Thermodynamics
State the first and second laws
of thermodynamics and explain
h they
how
h apply
l to liliving
i
organisms.
is the study of
energy changes.
„ Two fundamental laws govern all
energy changes in the universe. These
2 laws are simply called the first and
second laws of thermodynamics:
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Objective 20
Objective 20
„ First
Law:
¾ Energy can be converted from one
form to another, but it cannot be
created or destroyed.
¾ The total amount of energy in a closed
system remains constant.
„ Second
Law:
¾ Whenever an energy conversion takes
place, some of the energy gets
p
and
converted into a more dispersed
less useful form (usually random
molecular motion = heat).
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Objective 20
Objective 20
„ Free
energy (G) is a measure of the
amount of energy available to do
useful work. It depends on:
¾ the total amount of energy
g present;
p
this is called enthalpy (H)
¾ the amount of energy being used for
non--useful work (random molecular
non
motion); this is called entropy (S).
„ In
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Objective 20
summary, whenever an energy
change takes place in a closed system,
¾ the first law tells us the total energy
remains constant
¾ the
h second
d llaw tells
ll us ffree energy
decreases.
„ How is this possible?
¾ entropy increases! So closed systems
tend to become more disorganized.
general, ΔG = ΔH - T ΔS, where T
represents the temperature in degrees
Kelvin and Δ represent “the change
in”.
„ This means the amount of energy
available for useful work (G) equals
the total energy present (H) minus the
energy that is being wasted on random
molecular motion (S).
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Objective # 21
„ In
Explain what a chemical
reaction is and discuss how
chemical
h i l equations
i
are used
d to
describe the changes that take
place during a chemical reaction.
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Objective 21
of the changes that take place in
living organisms are the result of
chemical reactions.
„ What is a chemical reaction?
¾ As atoms and molecules move around,
they collide with each other. If they
collide with enough force, existing
chemical bonds can break and new
bonds can form.
Objective 21
„ Most
„ Chemical
equations can be used to
describe the changes that take place
during a chemical reaction:
CH4 + 2O2
C
Reactants
CO2 + 2H2O
C
Products
„ During
a chemical reaction no atoms
are created or destroyed.
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Objective 21
Objective # 22
„ Most
reactions are reversible:
¾ reading from left to right is called the
forward reaction
¾ reading
ead g from
o right
g t to left
e t iss called
ca ed the
t e
reverse reaction
„ At equilibrium
equilibrium,, the rate of the forward
reaction equals the rate of the reverse
reaction.
Distinguish between endergonic
and exergonic reactions and
explain how they are coupled in
living organisms. Describe the
roles of ATP and ADP in the
coupling of chemical reactions.
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Objective 22
Objective 22
„ All
atoms and molecules have a certain
amount of free energy:
¾ potential energy stored in the chemical
bonds that hold them together.
g
¾ kinetic energy due to their constant
random motion.
„ Large, complex molecules have more
free energy than small molecules.
„ Chemical
reactions involve a
change in free energy as well as
a change in the types of
molecules present.
present
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Objective 22
Objective 22
„ Exergonic
reactions::
reactions
„ the reactants have more free energy
than the products:
C6H12O6 + 6O2 → 6CO2 + 6H2O
more free
f energy
l free
less
f energy
„ involve a net release of energy and/or
an increase in entropy
„ occur spontaneously (without a net
input of energy)
„ Endergonic
reactions::
reactions
„ the reactants have less free energy
than the products:
6CO2 + 6H2O → C6H12O6 + 6O2
less free energy more free energy
„ involve a net input of energy and/or a
decrease in entropy
„ do not occur spontaneously
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Objective 22
Energy released E
Energy supplied
Exergonic and Endergonic Reactions
„ Living
Product
Energy
must be
supplied.
Reactant
Reactant
Energy is
released.
Product
Endergonic
Exergonic
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organisms have the ability to
couple exergonic and endergonic
reactions:
¾ energy
g released by exergonic
g
reactions
is captured and used to make ATP
from ADP and Pi
¾ ATP can be broken back down to
ADP and Pi, releasing energy to power
the cell’s endergonic reactions.
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ATP
„ Adenosine
triphosphate
„ The “energy currency” for all cells
„ Composed of
Structure of ATP
¾ Ribose
– 5 carbon sugar
¾ Adenine
¾ Chain of 3 phosphates
Key to energy storage
Bonds are unstable
„ ADP – 2 phosphates
„ AMP – 1 phosphate – lowest energy form
„
„
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Objective # 23
The ATP Cycle
Explain the concepts of
chemical equilibrium, transition
state, andd activation
i i energy.
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Objective 23
reactions, both endergonic and
exergonic, require an input of energy to
get started. This energy is called
activation energy.
energy.
„ Activation
A i i energy iis needed
d d to b
bring
i the
h
reactants close together and weaken
existing bonds. This produces an
unstable state of maximum potential
energy called the transition state.
state.
Energy released Energy supplied
„ All
Transition State
Activation
energy
Reactant
Product
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Objective # 24
Objective 24
„ In
most cases, molecules do not have
enough kinetic energy to reach the
transition state when they collide.
„ Therefore, most collisions are nonnonproductive, and the reaction proceeds
very slowly if at all.
„ What can be done to speed up these
reactions?
Describe some methods that
p
up
p
can be used to speed
chemical reactions.
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Objective 24
Activation Energy and Catalysis
Energy released Energy supplied
1) Add Heat – molecules move faster
so they collide more frequently and
with greater force.
2) Add a catalyst – a catalyst reduces
the energy needed to reach the
activation state, without being
changed itself. Proteins that function
as catalysts are called enzymes.
enzymes.
Activation
energy
Activation
energy
Reactant
Reactant
Product
Product
Uncatalyzed
Catalyzed
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Objective 24
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Objective # 25
„ Unlike
heat, which speeds up all
reactions indiscriminately, enzymes are
highly specific. Each enzyme typically
speeds up only one or a few similar
chemical reactions.
„ Therefore, by controlling which
enzymes are made, a cell can control
which reactions take place in the cell.
Describe the structure,
function,, and characteristics
of enzymes.
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Objective 25
Objective 25
„ Almost
all enzymes are globular
proteins with one or more pockets on
their surface called active sites.
sites.
„ Reactants bind to the active site to
form an enzyme
enzyme--substrate complex.
complex.
„ The 33-D shape of the active site and
the substrates must match, like a lock
and key.
„ Binding
of the substrates causes the
enzyme to adjust its shape slightly,
leading to a better induced fit
fit..
„ When this happens,
pp
the substrates are
brought close together and existing
bonds are stressed. This reduces the
amount of energy needed to reach the
transition state.
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Binding of the substrates causes the enzyme to adjust
its shape slightly, leading to a better induced fit.
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Objective # 26
Explain how the following factors
can affect enzyme activity:
a) temperature
b) pH
c) inhibitors and activators
d) cofactors
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Objective 26
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Objective 26a & b
„ The
rate of an enzyme
enzyme--catalyzed
reaction is affected by the
concentration of both the enzyme and
its substrates.
„ In addition, any physical or chemical
factors that affect the enzyme’s 33-D
shape can affect the enzyme’s ability to
catalyze the reaction
„ Temperature
and pH:
¾ Most enzymes have an optimum
temperature and an optimum pH.
These are related to the environment
where the enzyme normally functions.
¾ Enzyme activity decreases above or
below the optimum.
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Relationship of Enzyme Activity to pH
Optimum temperature for
human enzyme
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Optimum temperature for enzyme
from hotsprings prokaryote
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Optimum pH for pepsin
Optimum pH for trypsin
Rate of Re
eaction
Rate o
of Reaction
Relationship of Enzyme Activity to Temperature
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Temperature of Reaction (oC)
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pH of Reaction
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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Objective 26c
„
„
Objective 26c
Inhibitors and activators are
substances that bind to an enzyme
and affect its ability to catalyze a
reaction.
Activators bind to a region of the
enzyme called the allosteric site,
site,
thereby maintaining the enzyme’s
active configuration and its activity.
„ Inhibitors
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decrease enzyme activity in
one of 2 ways:
1)competitive
1)
competitive inhibitors bind to the
active site, thereby p
preventingg the
substrates from binding.
2)noncompetitive
2)
noncompetitive inhibitors bind to an
allosteric site, thereby altering the
shape of the active site so that it
cannot bind to the substrate.
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Substrate
Active
site
Substrate
Inhibitor
Active
site
Inhibitor
Enzyme
Enzyme
Allosteric site
When an inhibitor binds to the active site of
an enzyme and blocks the substrate from
binding, this is called…
When an inhibitor joins to an allosteric site and
alters the shape of the active site so it cannot
bind to the substrate, this is called…
Noncompetitive inhibition
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Competitive inhibition
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Objective 26d
Objective # 27
„ Cofactors
are nonprotein substances
required by enzymes in order to
function. For example, the active site
of many enzymes contain metal ions
that help draw electrons away from the
substrates.
„ Organic molecules that function as
cofactors are called coenzymes.
coenzymes.
Define the terms “metabolism”
and “metabolic pathway” (or
“bi h i l pathway”)
“biochemical
h ”) andd
explain how metabolic pathways
are regulated.
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Objective 27
refers to the sum of all
chemical reactions carried out by an
organism:
¾ reactions that jjoin small molecules
together to form larger, more complex
molecules are called anabolic.
anabolic.
¾ reactions that break large molecules
down into smaller subunits are called
catabolic..
catabolic
Objective 27
„ Metabolism
„A
sequence of chemical reactions,
where the product of one reaction
serves as a substrate for the next, is
called a metabolic pathway (or
biochemical pathway).
pathway).
„ Most metabolic pathways take place in
specific regions of the cell.
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Objective 27
„ The
regulation of simple metabolic
pathways often depends on feedback
inhibition::
inhibition
¾ the end p
product of the p
pathway binds
to an allosteric site on the enzyme that
catalyzes the first reaction and
inactivates it.
„ Why is the first reaction targeted?
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