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8.1
The laws of thermodynamics describe how energy changes.
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• Energy
is the capacity to bring about change, to provide motion against a force,
or to do work.
• Kinetic energy is actively engaged in doing work, while
potential energy has the capacity to do so.
• An oxidation-reduction (redox) reaction is one in which
an electron is taken from one atom or molecule (oxidation) and donated
to another (reduction).
• The First Law of Thermodynamics states that the amount
of energy in the universe is constant; energy is neither lost nor created.
• The Second Law of Thermodynamics states that disorder in
the universe (entropy) tends to increase.
• Any chemical reaction whose products contain less free
energy than the original reactants can proceed spontaneously. However,
the difference in free energy does not determine the rate of the reaction.
• The rate of a reaction depends on the amount of activation
energy required to break existing bonds.
• Catalysis is the process of lowering activation energies
by stressing chemical bonds.
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1. Define
oxidation and reduction. Why must these two reactions always occur in
concert?
2. State the First and Second Laws of Thermodynamics.
3. What is heat? What is entropy? What is free energy?
4. What is the difference between an exergonic and an endergonic
reaction? Which type of reaction tends to proceed spontaneously?
5. Define activation energy. How does a catalyst affect the final
proportion of reactant converted into product?
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8.2 Enzymes are biological
catalysts.
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•Enzymes
are the major catalysts of cells; they affect the rate of a reaction but
not the ultimate balance between reactants and products.
• Cells contain many different enzymes, each of which catalyzes
a specific reaction.
• The specificity of an enzyme is due to its active site,
which fits only one or a few types of substrate molecules.
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6. How are
the rates of enzyme-catalyzed reactions affected by temperature? What
is the molecular basis for the effect on reaction rate?
7. What is the difference between the active site and an allosteric
site on an enzyme?
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8.3 ATP is the energy
currency of life.
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• Cells
obtain energy from photosynthesis and the oxidation of organic molecules
and use it to manufacture ATP from ADP and phosphate.
• The energy stored in ATP is then used to drive endergonic
reactions.
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8. What part
of the ATP molecule contains the bond that is employed to provide energy
for most of the endergonic reactions in cells?
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8.4 Metabolism is the
chemical life of a cell. .
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• Generally,
the final reactions of a biochemical pathway evolved first; preceding
reactions in the pathway were added later, one step at a time.
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9. What is
a biochemical pathway? How does feedback inhibition regulate the activity
of a biochemical pathway?
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