Download Energy and the Cell 5.10-5.15

ENERGY AND THE CELL
5.10-5.15
5.10 Cells transform energy as they perform work
• Cells are small units, a chemical factory, housing
thousands of chemical reactions.
• Energy may be used or released during these
reactions.
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5.10 Cells transform energy as they perform work
• Energy is the capacity to cause change or to
perform work.
• There are two kinds of energy.
1. Kinetic energy is the energy of motion
• Transfer motion to other matter (legs pushing
bike pedals)
• Heat/thermal energy: random motion of
molecules
• Light energy: photosynthesis
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5.10 Cells transform energy as they perform work
1. Potential energy is energy that matter possesses
as a result of its location or structure.
• Bike at the top of a hill
• Water behind a dam
• Chemical energy: used to power cells
5.10 Cells transform energy as they perform work
• Thermodynamics: the study of energy
transformations
• First law of thermodynamics: energy can be
transferred or transformed, but it cannot be
created or destroyed.
– Batteries transform stored energy into electric energy
– Plants: light is transformed into chemical energy
(photosynthesis)
– Cellular respiration: chemical energy is converted to a
form the cell can use (ATP) to do work
5.10 Cells transform energy as they perform
work
• The second law of thermodynamics: energy
conversions create entropy.
– A measure of disorder
• During energy transformations some energy is
converted to heat which disordered energy
and unable to do work
Figure 5.10
Energy conversion
Fuel
Waste products
Heat
energy
Carbon dioxide
Gasoline

Combustion
Kinetic energy
of movement

Water
Oxygen
Energy conversion in a car
Heat
energy
Cellular respiration
Glucose

Oxygen
Carbon dioxide
ATP
ATP
Energy for cellular work
Energy conversion in a cell

Water
5.11 Chemical reactions either release or store energy
• Chemical reactions either
– release energy (exergonic reactions)
• Burning sugar such as a marshmallow (fast)
• Cellular respiration (slow)
– require an input of energy and store energy
(endergonic reactions).
• Products of the reaction contain more energy than the
reactants
– photosynthesis
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Potential energy of molecules
Figure 5.11A
Reactants
Amount of
energy
released
Energy
Products
Potential energy of molecules
Figure 5.11B
Products
Energy
Reactants
Amount of
energy
required
5.11 Chemical reactions either release or store energy
• The total of an organism’s chemical reactions is
called metabolism.
• A metabolic pathway
– builds a complex molecule or
– breaks down a complex molecule into simpler
compounds.
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5.11 Chemical reactions either release or store energy
• Energy coupling uses the
– energy released from exergonic reactions to drive
– essential endergonic reactions,
– usually using ATP molecules.
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5.12 ATP drives cellular work by coupling exergonic and
endergonic reactions
• ATP, adenosine triphosphate, powers nearly all
forms of cellular work.
© 2012 Pearson Education, Inc.
5.12 ATP drives cellular work by coupling exergonic and
endergonic reactions
• Hydrolysis of ATP releases energy by transferring
its third phosphate from ATP to some other
molecule in a process called phosphorylation.
• Most cellular work depends on ATP energizing
molecules by phosphorylating them.
© 2012 Pearson Education, Inc.
Figure 5.12A_s1
ATP:
Adenosine Triphosphate
Phosphate
group
P
Adenine
Ribose
P
P
Figure 5.12A_s2
ATP:
Adenosine Triphosphate
Phosphate
group
P
P
P
Adenine
Ribose
Hydrolysis
P
ADP:
H2O
P
Adenosine Diphosphate
P
Energy
Figure 5.12B
Chemical work
Mechanical work
Transport work
ATP
ATP
ATP
Solute
P
Motor
protein
P
P
Reactants
Membrane protein
P
P
P
Product
Molecule formed
ADP
P
Protein filament moved
ADP
P
Solute transported
ADP
P
5.12 ATP drives cellular work by coupling exergonic and
endergonic reactions
• ATP is a renewable source of energy for the cell.
•.
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Figure 5.12C
ATP
Energy from
exergonic
reactions
ADP
P
Energy for
endergonic
reactions
HOW ENZYMES FUNCTION
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5.13 Enzymes speed up the cell’s chemical reactions by
lowering energy barriers
• Although biological molecules possess much
potential energy, it is not released
spontaneously.
– An energy barrier must be overcome before a
chemical reaction can begin.
– This energy is called the activation energy (EA).
© 2012 Pearson Education, Inc.
Figure 5.13A
Activation
energy barrier
Enzyme
Activation
energy
barrier
reduced by
enzyme
Reactant
Energy
Energy
Reactant
Products
Without enzyme
Products
With enzyme
Figure 5.13Q
Energy
a
b
Reactants
c
Products
Progress of the reaction
5.13 Enzymes speed up the cell’s chemical reactions by
lowering energy barriers
• Enzymes
– function as biological catalysts by lowering the EA
needed for a reaction to begin,
– increase the rate of a reaction without being
consumed by the reaction, and
– are usually proteins, although some RNA molecules
can function as enzymes.
• Hydrolysis of sucrose
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Figure 5.14_s4
1
Enzyme available
with empty active
site
Active site
Substrate
(sucrose)
2
Glucose
Substrate binds
to enzyme with
induced fit
Enzyme
(sucrase)
Fructose
H2O
4
Products are
released
3
Substrate is
converted to
products
5.14 A specific enzyme catalyzes each cellular reaction
• For every enzyme, there are optimal conditions
under which it is most effective.
• Environment affects protein shape
• Temperature affects molecular motion.
– Most human enzymes work best at 35–40ºC.
• The optimal pH for most enzymes is near
neutrality.
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5.15 Enzyme inhibitors can regulate enzyme activity in a
cell
• A chemical that interferes with an enzyme’s activity is called an
inhibitor.
• Competitive inhibitors (many drugs and poisons)
– block substrates from entering the active site and
– reduce an enzyme’s productivity.
• Noncompetitive inhibitors
– bind to the enzyme somewhere other than the
active site,
– change the shape of the active site, and
– prevent the substrate from binding.
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Figure 5.15A
Substrate
Active site
Enzyme
Allosteric site
Normal binding of substrate
Competitive
inhibitor
Noncompetitive
inhibitor
Enzyme inhibition
5.15 Enzyme inhibitors can regulate enzyme activity in a
cell
• Enzyme inhibitors are important in regulating cell
metabolism.
.
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5.16 CONNECTION: Many drugs, pesticides, and poisons
are enzyme inhibitors
• Many beneficial drugs act as enzyme inhibitors,
including
– Ibuprofen, inhibiting the production of
prostaglandins,
– some antidepressants,
– protease inhibitors used to fight HIV.
• Enzyme inhibitors have also been developed as
pesticides and deadly poisons for chemical
warfare.
© 2012 Pearson Education, Inc.