Transcript 11 Thermodynamics 9 26 05

BCOR 011
Lecture 11
Chapter 8
The Flow of Energy in a Cell
Sept 26, 2005
1
Figure 8.1
Energy: the capacity to effect change
Two types of energy
Potential Energy
Kinetic Energy
-stored in height
-energy of movement
-stored in battery (conc/charge)
-stored in BONDS
-molecules colliding, vibrating
-HEAT, light
2
Potential Energy Stored in:
Figure 8.2
location
Figure 8.5
On the platform, a diver
Diving converts potential
has more potential energy. energy to kinetic energy.
Chemical
bonds
gradient
Climbing up converts kinetic
energy of muscle movement
to potential energy.
In the water, a diver has
less potential energy.
3
1st Law of Thermodynamics
Energy is neither created nor destroyed in
chemical reactions
but only Transformed from one form to another
Potential
Potential
Kinetic
Kinetic
4
In a chemical reaction
products have a lower potential energy than reactants
Atoms bonded in
High Potential Energy
Configuration
Energy is Released
Atoms bonded in
Low Potential Energy
Configuration
5
a Chemical Reaction
Example
- -
H
H-C-H
H
Reorganization of Bonds of existing molecules
- an exchange
O=C=O
O=O
O=O
Same # of H’s
Same # of C’s
Same # of O’s
H
O
H
H
O
H
All Start with filled outer shell of electrons
All End with outer shell of electrons
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High Energy
H
H-C-H
H
-
reduced
-
O=O
H
O=C=O
H
O
ENERGY
RELEASED
oxidized
Low Energy
7
Energy that is released:
Has the capacity to DO WORK
Raise potential state of something else
Or effect movement – heat, motion
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Types of Work:
1
Biosynthetic: changes in chemical bonds
A + B
reactants
C + D
products
A+B
G+H
C+D
E+F
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Other Types of Work
2. Chemical Concentration Gradient
Ainside + Boutside
even
even
Aoutside + Binside
low
high
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3. Electrical work – movement of ions across
a membrane against an electrochemical gradient
Ainside + Boutside
even
even
Aoutside + Binside
+
-
11
Other Types of Work
4
Mechanical Work: Movement, Motility
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Another form of
MOVEMENT
Relaxed
Low Energy
Conformation
A
Conformation
B
Poised
13
High Energy
• Some organisms
– Convert energy to light, as in bioluminescence
Figure 8.1
14
Energy that is released:
Has the capacity to DO WORK
Raise potential state of something else
Or effect movement – heat, motion
But some is always lost to disorder
15
Change
In potential
Energy
State 1
State 2
Gross Pay
Released Energy
Ability
To do + Randomness
work
Take
Home +
Pay
Taxes
16
Kinetic Energy can be dissipated:
Randomized
Releases Energy
Kinetic Energy
Sound
Floor Vibration
Disorder
Requires
Energy Input
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Second law of Thermodynamics:
The Universe is proceeding to a
State of MAXIMUM DISORDER
Only time this is not true
is when no movement anymore
ie. at abosolute zero
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0o K - no motion, no “taxes”
A Progressive Scale:
Higher the temperature,
the more that disorder comes into play
higher proportion of energy lost to randomness
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Change
In potential
Energy
State 1
State 2
Enthalpy
DH
Released Energy
Ability
To do + Randomness
work
Free
Energy +
DG
Entropy
T DS
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ENTHALPY
DH
Change in
Chemical Bond
Energy
ENTROPY
DS
(disorder)
Freedom of
Movement
or
Position
Randomness
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Change in
Chemical Bond
Energy
ENTHALPY
DH
Time
High
Potential
High
Potential
Low Potential
Glucose
+
6 O2
6 CO2
+
6 H2O
-DH
Low Potential
6 Glucose 6 CO2
+
+
6 O2
6 H2O
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ENTROPY
DS
Number of
possible states
that can be
present in:
Change in
Freedom
Roll of “2”
Low entropy
Only 1 possible
“state”
Roll of “7”
High entropy
6 possible
“states”
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ENTROPY
DS
Few
States
Change in
Freedom
Many
States
“Dispersed”
Number of
Possible States
That can be
Present in
Few
States
Many
States
“Dispersed”
time
Na+ ClNaCl
crystal ions in water
Na+ ClNaCl
crystal ions in water
+DS
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The Free Energy Change
DG
Dictates whether a reaction will
Proceed spontaneously or not
Whether a Reaction is
Favorable or Unfavorable
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Change in
Chemical
Bond
Energy
Energy that
Goes to
Do Useful Work
Energy that
Goes to
Randomness
Dependent
On
Entropy
Temperature
Enthalpy
“free energy”
(Gibb’s Free Energy)
Kinetic Movement
DH
=
TDS
DG
=
+
DH -
If DG = negative #
reaction is energetically favorable
DG
TDS
“spontaneous”
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DG = DH – TDS
- DG is favorable exergonic “spontaneous”
+ DG is NOT favorable, endergonic, nonspontaneous27
An exergonic reaction
– Proceeds with a net release of
free energy and is spontaneous
“will happen”
Reactants
Free energy
Amount of
energy
released
(∆G <0)
Energy
Products
Progress of the reaction
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Figure 8.6 (a) Exergonic reaction: free
energy released
An endergonic reaction
– Is one that absorbs free energy from its
surroundings and is nonspontaneous
“doesn’t happen”
Free energy
Products
Energy
Amount of
energy
released
(∆G>0)
Reactants
Progress of the reaction
Figure 8.6
(b) Endergonic reaction: energy required
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2 Factors Contribute to Whether a Reaction will Occur:
change in Bond Energy
Reduced
Oxidized
The sum of these is the
change in Entropy
Complex
Simple
Net Useful Energy (DG)
net ENERGY RELEASED - EXERGONIC = FAVORABLE
If require net ENERGY INPUT - ENDERGONIC = UNFAVORABLE
If
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Complex
Simple
change in Entropy
Reduced (no oxygens)
Lower
H H HHH HH H
H-C-C-C-C-C-C-C-C-H
H HH HH HH H
hydrocarbon
8
fats
H
H-C-H
H
H
R-C-OH
H
alcohol
O
=
sugars
R-C-H
aldehyde
O
=
change in Bond Energy
High
R-C-OH
Final
product
acid
O=C=O
Low
Carbon
31 dioxide
Oxidized
Lowest
EXERGONIC REACTIONS
gasoline burns
iron rusts
hydrogen and oxygen form water (explosive!)
Either: go to bonding arrangement with lower potential energy
Or: go from a more complex state to a simpler state
1 molecule of 8 carbons
vs
8 molecules of 1 carbon
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DH=
DS=
+
DG= very -
favorable
favorable
favorable
2
Spontaneous
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Favorable - it can happen
DH = Hproducts -Hreactants
 DH
exothermic
Heat released
+ DH
endothermic
Heat input
icepack
34
DH=
DS=
DG=
+
+
-
Unfavorable
Very favorable
favorable
Entropy Driven Reaction
Spontaneous
Favorable - it can happen 35
Entropy overwhelms Enthalpy
DH=
DS=
DG=
-
very favorable
unfavorable
favorable
Enthalpy Driven Reaction
Spontaneous
Favorable - it can happen
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Enthalpy overweighs Entropy
DG = DH – TDS DG = DH – TDS DG = DH – TDS
(-) - (+) (-) - (-) (+) - (+)
Spontaneous
Enthalpically
Entropically
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Favorable Rxn
Driven Rxn
Driven Rxn
DH=
DS=
DG=
+
+
unfavorable
unfavorable
unfavorable
Non-spontaneous
NOT Favorable - it can NOT happen
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A typical
ENDERGONIC/Unfavorable/NonSpontaneous REACTION
- building a polymer
Monomer + Monomer
Polymer + Water
Requires 5.5 energy units
WILL NOT OCCUR
How could we make it occur?
If have a captured packet of energy of 7.3 energy units
Integrate
an exergonic reaction with an endergonic reaction
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COUPLED Reactions
Tie a favorable rxn with
An otherwise unfavorable rxn
Drive otherwise unfavorable
reactions
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DG = +5.5
kcal/mole
1.
2. ATP+ H2O
DG = -7.3
kcal/mole
ADP + Pi
ATP
ADP + Pi
Favorable or unfavorable41 ?
Note:
Each step is
favorable
Net
DG = -7.3 kcal/mole
+DG = +5.5 kcal/mole
rxn DG = -1.8 kcal/mole
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Coupled Reaction
ADP -P
+ monomer1
ADP-monomer1
(ATP)
+ P
I’m free!
DG = -1.0
ADP-monomer1 + monomer 2
Now tied together
ADP +
monomer1-monomer 2
Now I’m free too!
DG = -0.8
7.3 units released
Net: ATP +H2O
monomer1 + monomer2
5.5 units needed
ADP + P
monomer1-monomer2 + H2O
DO NOT LET ATP FALL APART IN 1 STEP,
use energy in its bond to MAKE the polymer linkage
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Another Example of a Coupled Reaction
Endergonic reaction: ∆G is positive, reaction
is not spontaneous
NH2
Glu
+
Glutamic
acid
NH3
Glu
Ammonia
Glutamine
∆G = +3.4 kcal/mol
Exergonic reaction: ∆ G is negative, reaction
is spontaneous
ATP
Figure 8.10
+
H2O
ADP +
Coupled reactions: Overall ∆G is negative;
together, reactions are spontaneous
P
∆G = + 7.3 kcal/mol
∆G = –3.9 kcal/mol
44
Three types of cellular work powered by
ATP hydrolysis
Physical
movement
P
i
P
Motor protein
Driving
Conformational
Changes
ADP
Of
+
P
Proteins
Protein moved
(a) Mechanical work: ATP phosphorylates motor proteins
Membrane
protein
ActiveATP
Transport
Pumps
i
P
Solute
P
i
Solute transported
(b) Transport work: ATP phosphorylates transport proteins
P
Glu +
NH2
Reactants: Glutamic acid
and ammonia
Figure 8.11
+
NH3
P
i
Glu
Product (glutamine)
made
(c) Chemical work: ATP phosphorylates key reactants
Biosynthetic
Coupled
Rxn45
Equilibrium
Reactions in a closed system
– Eventually reach equilibrium
∆G < 0
Figure 8.7 A
∆G = 0
(a) A closed hydroelectric system. Water flowing downhill turns a turbine
that drives a generator providing electricity to a light bulb, but only until
the system reaches equilibrium.
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In living systems
– Experience a constant flow of materials in
– Constant Energy Input
∆G < 0
(b) An open hydroelectric
system. Flowing water
keeps driving the generator
because intake and outflow
of water keep the system
from reaching equlibrium.
Figure 8.7
47
cellular respiration is a series of favorable reactions
∆G < 0
∆G < 0
∆G < 0
Figure 8.7
(c) A multistep open hydroelectric system. Cellular respiration is
analogous to this system: Glucoce is brocken down in a series
of exergonic reactions that power the work of the cell. The product
of each reaction becomes the reactant for the next, so no reaction
reaches equilibrium.
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For example, oxidation of glucose:
C6H12O6 (glucose) + 6O2
DG= -686 kcal/mol
6CO2 + 6H2O
DH = -673 kcal/mol
TDS= -13 kcal/mol
in the cell, this is done in >21 steps!
Capture the energy in small packets
ie, 36 ATP units of 7.3 kcal
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Summary:
-matter is neither created nor destroyed
-the universe is proceeding toward disorder
DH = enthalpy (heat content,bond energy)
DS = entropy (randomness)
DG = free energy (available to do work)
DG = DH - TDS
- coupled reactions
-biological systems always need
constant energy input
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