Chapter 3 Energy, Catalysis, and Biosynthesis
By maintaining
highly ordered states,
cells seemingly defy
the laws of
thermodynamics:
1) There is a finite
amount of energy in
the universe. It can
neither be created nor
destroyed, only
changed from one
form to another.
2) A change will always
be accompanied by
an increase in disorder
(entropy).
Fig. 1-7
The same principle applies to our everyday lives.
A housewife’s work is never done….Neither is the cell’s.
High Entropy
Fig. 3-4
Low Entropy
Chemical Energy from Glucose
Used by Cells to Maintain Order
Low Entropy
ATP
energy consuming
energy releasing
Fig. 3-2
High Entropy
Thermodynamics: Study of Energy Transformations
Fig. 3-6
All energy required to maintain life is derived from the sun.
Fig. 3-7
Vincent van Gogh
Photosynthesis Makes Sugars for Cellular Respiration
Fig. 3-6
Cells Do Not Defy the Laws of Thermodynamics
in the Context of the Whole Universe
disorder everywhere
Fig. 3-5
CO2 and H2O
-catabolism
macromolecules
organelles, etc.
-anabolism
Study of Energy Transformations:
Thermodynamics
early
Steam Engine
began w/ invention of steam engine
Gibbs Free Energy Equation:
DH
=
DG
+
TDS
Work
Energy
Potential
Energy
Energy Lost
to Disorder
Rearranged:
DG
=
DH
-
TDS
∆G measures likelihood a reaction will occur
Exergonic: DG < 0- will occur w/o external energy
Endergonic: DG > 0- will NOT occur w/o external energy
DG
=
DH
-
Chemical
Bond Energy
TDS
DG < 0 (will occur w/o external energy) when:
DH<0 and DS > 0
Products have lower bond energies than Reactants (DH<0)
& Products more disordered than Reactants (DS>0)
OR DH<<<<0 and DS < 0
OR DH>0 and DS >>>> 0
< Cell
.
Respiration
Cell Respiration: DH <<< 0 allows DS < 0
Fig. 3-4
DG
=
DH
-
TDS
Chemical Energy from Glucose
Used to Synthesize Macromolecules
energy releasing
DG < 0
DH < 0, DS > 0
Fig. 3-2
energy consuming
DG > 0
DH > 0, DS < 0
requires external
energy (ATP)
How Can Endergonic Reactions
(DG >0) Occur in Cells?
principle applies to
individual reactions too
One mechanism is to
couple it to a highly
exergonic reaction.
catabolism
Fig. 3-17
anabolism
Chemical Energy from Glucose
Used to Synthesize Activated Energy Carriers
Activated
Energy
Carriers
energy consuming
energy releasing
ATP, NAD(P)H2
Fig. 3-2
Energy from Glucose Oxidation Stored
in Activated Energy Carrier, ATP
synthesis
Fig. 3-31
hydrolysis
Exergonic ATP Hydrolysis Often
Coupled to Endergonic Reactions
coupled in
parallel
Panel 3-1g
NADH and NADPH are
Activated Carriers of Electrons
Electrons are transferred
from glucose to these
portable electron carriers.
Fig. 3-34
.
DG under non-standard conditions (in cells)
depends on true concentrations of molecules
DG = DGo + RT ln [Product]
[Reactant]
Rxn 1
DG>0
Rxn 2
DG<<0
coupled in
sequence
Coupled Rxn
DG<0
Rxn 2 keeps [Prod]/[React] of Rxn 1 low
Fig. 3-21
.
will occur without external energy, but not on useful timescale
Enzymes Increase the Velocity of a Reaction
(Not the Thermodynamics)
with enzyme
without enzyme
Fig. 3-27b (modified)
Enzymes Lower Activation Energy
Fig. 3-12
Enzymes Lower Activation Energy
reduce size of barrier
Fig. 3-14
By Lowering Activation Energy
at Discrete Steps, Enzymes
Direct Reaction Pathways
to Specific Products
Fig. 3-14
Enzymes are not altered by the reactions they catalyze.
They are used over and over again.
Fig. 3-15
Enzymes allow the cell to extract energy from glucose
in small steps, instead of all at once in the form of heat.
Some energy can be harnessed for useful work.
Fig. 3-30
How Do Enzymes Lower the Activation Energy?
Fig. 4-36
Example: Lysozyme
bond bent, then broken by enzyme
Amino acid side chains at active site strain bonds of substrate and
alter its chemical properties to ease it into activated transition state.
Fig. 4-35
Measuring Enzyme Performance
Fig. 3-27
v = Vmax [S]
KM + [S]
Michaelis- Menten
equation describing
enzyme performance
Lineweaver-Burke
Double Reciprocal Plot Allows for
Easier Determination of Vmax and KM
y intercept at x = 0
x intercept at y = 0
Fig. 3-27c
1/v = KM (1/[S]) + 1/Vmax
Vmax
straight line formula:
y = a(x) + b
Enzyme Kinetic Assays Used to
Determine Competitor Type
+ competitive
inhibitor
succinate
binds active site
noncompetitive
binds
elsewhere
+ noncompetitive
inhibitor
+ noncompetitive
inhibitor
+ competitive
inhibitor
Fig. 3-29
competitive: affects KM only
non-competitive: affects Vmax only
Vmax / Vmax
Determining
KM and Vmax
Vmax
KM increased;
Vmax not changed
KM = [S] at ½ Vmax
Vmax decreased;
KM not changed
y intercept = 1/Vmax
x intercept = -1/KM
enzyme alone
+ competitive inhibitor
+ noncompetitive inhibitor