Bioenergetics and Thermodynamics
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Learning Objectives
At the end of the lesson, students should be able to:
Forms of Energy
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The Laws of Energy Transformation
Thermodynamics
-The branch of science studying heat, energy and the ability of the energy to do work
The First Law of Thermodynamics
(The Law of Energy Conservation)
“The Amount Of Energy In The Universe Is Constant”
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[Is the study of energy transformations]
Energy can be converted from one form to another
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An example of energy conversion
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System
Bioenergetics and Thermodynamics
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Enthalphy (H)
Bioenergetics and Thermodynamics
Bioenergetics and Thermodynamics
Enthalphy change (∆H)
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Enthalphy change (∆H)
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The Second Law of Thermodynamics
Bioenergetics and Thermodynamics
Entropy (S)
Entropy (∆S)
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Particles in:
Particles in:
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Entropy (S)
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Predicting the sign of ∆S
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Relationship between energy and entropy
DH = change in enthalpy
DS = change in entropy ; T = degree Kelvin
∆G = ∆H – T∆S
(at constant temperature and pressure)
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Relationship between energy and entropy
∆G = ∆H – T∆S
(at constant temperature and pressure)
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Standard Temperature = 298K (25oC)
Standard Pressure = 1 atmosphere
Standard Solute Concentration = 1.0M
Standard H+ concentration = 10-7 (pH = 7.0)
H2O concentration = 55.5 M
Standard Free-Energy Change (DGo)
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∆Go' = standard free energy change (at pH 7, 1M reactants & products); R = gas constant; T = temp)
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Free-Energy Change
Free-Energy Change, ΔG
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Free-Energy Change
Free-Energy Change, ∆G
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Energy coupling
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For example, in the reaction catalyzed by the Glycolysis enzyme Hexokinase, the half-reactions are:
ATP + H2O ↔ ADP + Pi ∆Go' = -31 kJ/mol
Pi + glucose ↔ glucose-6-P + H2O ∆Go' = +14 kJ/mol
Coupled reaction:
ATP + glucose ↔ ADP + glucose-6-P ∆Go' = -17 kJ/mol
Energy coupling
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Adenosine Triphosphate (ATP)
Bioenergetics and ATP
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Phosphoanhydride have a large negative DG of hydrolysis.
“High energy” bonds
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O
O
O
O
CH2
H
OH
OH
H
N
H
H
O
N
C
HC
N
C
C
N
NH2
Adenine
Ribose
Phosphate groups
O
O
O
O
O
O
-
-
-
-
CH
The Structure and Hydrolysis of ATP
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Energy
Adenosine triphosphate (ATP)
Inorganic phosphate
Adenosine diphosphate (ADP)
Energy is released from ATP when the terminal phosphate bond is broken (hydrolysed)
The Structure and Hydrolysis of ATP
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Endergonic reaction: ∆G is positive, reaction
is not spontaneous
∆G = +3.4 kcal/mol
Glu
Glu
∆G = - 7.3 kcal/mol
ATP
H2O
+
+
NH3
ADP
+
NH2
Glutamic
acid
Ammonia
Glutamine
Exergonic reaction: ∆ G is negative, reaction
is spontaneous
P
Coupled reactions: Overall ∆G is negative;
together, reactions are spontaneous
∆G = –3.9 kcal/mol
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Other examples of high energy compounds
Phosphocreatine
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Other examples of high energy compounds
Phosphoenolpyruvate (PEP)
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An exergonic reaction
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Reactants
Products
Energy
Progress of the reaction
Amount of
Energy released �(∆G <0)
Free energy
(a) Exergonic reaction: energy released
Exergonic and Endergonic Reactions in Metabolism
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Energy
Products
Amount of
Energy released �(∆G>0)
Reactants
Progress of the reaction
Free energy
(b) Endergonic reaction: energy required
Exergonic and Endergonic Reactions in Metabolism
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Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium.
∆G < 0
∆G = 0
Equilibrium and Metabolism
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(b) An open hydroelectric � system. Flowing water� keeps driving the generator � because intake and outflow � of water keep the system � from reaching equlibrium.
∆G < 0
Cells in our body
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(c) A multistep open hydroelectric system. Cellular respiration is � analogous to this system: Glucoce is broken 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.
∆G < 0
∆G < 0
∆G < 0
Think!
What does ΔG tell us about a biochemical reaction?
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