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Unformatted text preview: Energy storage and transformation 1 Last Time
Types of energy Thermodynamics Energy use in ecosystems movement of energy movement of chemicals Hierarchies in ecosystems Nutrient cycling
2 Energy and material flow
Measuring the energy that can perform work in the cell - Free energy - G Free energy and metabolism - exergonic and endergonic reactions Coupling exergonic reactions with endergonic reactions to do work 3 What is Life? http://en.wikipedia.org/wiki/Erwin_Schr%C3%B6dinger Erwin Schrdinger Life avoids decay by virtue of metabolism - building order out of disorder
4 www.amazon.com Fig 8.2 high potential energy "unstable" low potential energy "stable" 5 How do we know which reactions will occur without energy input?? How do we know which reactions require energy to occur?? 6 Gibbs free energy (G)
- energy that can perform work in the system under uniform conditions (e.g. a cell) for a given chemical reaction: G = H - TS
change in free energy temp in change in the Kelvin total energy in a closed system change in system's entropy 7 G - a measure of the tendency to change
higher G in initial state "unstable" G = Gfinal - Ginitial
lower G in final state "stable" 8 Water here = high potential energy (location), low entropy Water here = low potential energy, high entropy water is moving from high to low potential energy each step is contributing to entropy Fig. 8.7
9 Reactions at equilibrium have a G = 0
If cell's reactions is at equilibrium - there is no free energy, thus no energy to do work and the cell is dead. defining feature of life is that an organism is never at equilibrium Fig. 8.7
Free energy is the energy that can be used to do work in the system G is a measure of free energy of a given reaction. If: G < 0, the process is spontaneous, does not require energy G > 0, the process requires energy to proceed G = 0, there is no energy available for work
11 Two types of reactions in metabolism
Exergonic - "energy outward" - releases energy, occurs spontaneously, G is negative Endergonic - "energy inward" - absorbs energy from surroundings, requires energy to occur, G is positive 12 Exergonic reactions
C6H1206 + 602 6 CO2 + 6 H20 G = -686 kcal/mol 13 Endergonic reactions
6 CO2 + 6 H20 C6H1206 + 602 G = +686 kcal/mol 14 Summary
Two types of metabolic reactions: endergonic reactions - require energy - G > 0 - e.g. synthesis of macromolecules, dehydration reactions exergonic reactions - release energy - G < 0 - e.g. breakdown of macromolecules, hydrolysis reactions
15 Cells do three kinds of work
1. Mechanical 2. Transport 3. Chemical 16 Cell does work by...
...Energy coupling! - uses an exergonic process to drive an endergonic one
endergonic reaction exergonic reaction 17 ATP
Provides the energy used by the cell to do work G of ATP hydrolysis = -7.3 kcal/mol
18 Fig. 8.9 19 Using ATP to couple exergonic and endergonic reactions
Endergonic reaction Exergonic reaction 20 Fig. 8.12 Kinases couple the energy of ATP hydrolysis to endergonic processes to "do work"
21 Energy released from exergonic reactions is used for endergonic reactions in the cell Fig. 8.12
Measuring the energy that can perform work in the cell - Free energy - G Free energy and metabolism - exergonic and endergonic reactions Coupling exergonic reactions with endergonic reactions to do work 23 Next Time
Enzymes (and Quiz 2) 24 ...
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- Spring '08