Download An Introduction to Metabolism

Chapter 8
An Introduction to
Metabolism
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: The Energy of Life
• The living cell
– Is a miniature factory where thousands of
reactions occur
– Converts energy in many ways (ex: Convert
energy to light, as in bioluminescence)
Figure 8.1
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Metabolism…What is it?
• Is the totality of an organism’s chemical
reactions
– Arises from interactions between molecules
• A metabolic pathway has many steps
– That begin with a specific molecule and end
with a product
– That are each catalyzed by a specific enzyme
Enzyme 1
A
Enzyme 2
D
C
B
Reaction 1
Enzyme 3
Reaction 2
Starting
molecule
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Reaction 3
Product
Two Types of Pathways
• Catabolic pathways
– Break down complex molecules into simpler
compounds
– Release energy (-G)
• Anabolic pathways
– Build complicated molecules from simpler ones
– Consume energy (+ G)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Two Types of Energy
• What is Energy?
– Is the capacity to cause change
– Exists in various forms, of which some can
perform work
• Two Types of Energy
– Kinetic energy - Is the energy associated with
motion
– Potential energy - Is stored in the location of
matter. This Includes chemical energy stored
in molecular structure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Conversion of energy
On the platform, a diver
has more potential energy.
Figure 8.2
Climbing up converts kinetic
energy of muscle movement
to potential energy.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Diving converts potential
energy to kinetic energy.
In the water, a diver has
less potential energy.
The First Law of Thermodynamics
• Energy can be transferred and transformed
• Energy cannot be created or destroyed
Chemical
energy
(a)
Figure 8.3
First law of thermodynamics: Energy
can be transferred or transformed but
Neither created nor destroyed. For
example, the chemical (potential) energy
in food will be converted to the kinetic
energy of the cheetah’s movement in (b).
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Second Law of Thermodynamics
• Every energy transfer makes universe more
disordered = increases entropy
–
When energy is transferred – some lost as heat
–
Amount of useful energy decreases when energy
is transferred
Heat
co2
+
H2O
Figure 8.3
(b) Second law of thermodynamics: Every energy transfer or transformation increases
the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s
surroundings in the form of heat and the small molecules that are the by-products
of metabolism.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Problem:
• Living organisms are highly ordered: decrease
entropy.
• For example, Living organisms take in
disordered amino acids and order them in the
form of proteins.
Question: Do living organisms violate the second
law?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
NO
• Living organisms also take in ordered forms (starch)
and break them into smaller more disordered units
(glucose)
• Must consider organism and their environment
• Living organisms
– Maintain highly ordered structure at the expense of
increased entropy of surroundings
– Take in complex high energy molecules, extract
energy, release simpler low energy molecules (CO2
and H20) and heat to environment
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Energy Exchanges
• Free energy (∆G) = work that can be performed
by cell when Temp & pressure are uniform
• The change in free energy, ∆G during a
biological process
– Is related directly to the enthalpy change (∆H)
and the change in entropy (∆S)
∆G = ∆H – T∆S
∆H = change in enthalpy = heat of reaction
T = temperature (K)  °C + 273
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Free Energy, Stability, and Equilibrium
• Organisms live at the expense of free energy
• During a spontaneous change
– ∆G is negative
• During every energy exchange (∆H) some
energy is available to do work (∆G) and some
is lost to the system (T∆S)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• At maximum stability
– The system is at equilibrium
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneously change
• The free energy of the system
decreases (∆G<0)
• The system becomes more stable
• The released free energy can
be harnessed to do work
.
• Less free energy (lower G)
• More stable
• Less work capacity
(a) Gravitational motion. Objects
move spontaneously from a
higher altitude to a lower one.
Figure 8.5
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(b) Diffusion. Molecules
in a drop of dye diffuse
until they are randomly
dispersed.
(c) Chemical reaction. In a
cell, a sugar molecule is
broken down into simpler
molecules.
Exergonic and Endergonic Reactions in Metabolism
• An exergonic reaction
– Proceeds with a net release of free energy and
is spontaneous
Reactants
Free energy
Amount of
energy
released
(∆G <0)
Energy
Products
Progress of the reaction
Figure 8.6
(a) Exergonic reaction: energy released
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Exergonic Reactions
R
E
n
e
r
g
y
P
Time
•Reactants have more
energy
•More ordered to less
•Unstable to stable
•Downhill reaction
•Free energy released
•∆G is negative
•Spontaneous
•Examples:
– Cellular Respiration
– Digestion
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• An endergonic reaction
– Is one that absorbs free energy from its
surroundings and is nonspontaneous
Free energy
Products
Amount of
energy
released
(∆G>0)
Energy
Reactants
Progress of the reaction
Figure 8.6
(b) Endergonic reaction: energy required
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Endergonic Reactions
P
E
n
e
r
g R
y
Time
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Products have more
energy than reactants
•Less ordered to more
•Stable to unstable
•Uphill reaction
•Free energy absorbed
from surroundings
•∆G is positive
•Examples:
– Photosynthesis
– Polymer synthesis
Couple Reactions
•Energy released from
exergonic reaction drives
endergonic reaction
R
E
n
e
r
g
y
P
Time
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
•Exergonic reaction ∆G =
maximum work that can be
done
•Endergonic reaction ∆G =
minimum work needed to
drive the reaction
Let’s check out a video
Bozeman Science – Paul Andersen
Website: www.bozemanscience.com
Gibb’s Free Energy:
http://www.bozemanscience.com/sciencevideos/2011/9/14/gibbs-free-energy.html
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings