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Chapter 7 EEnneerrggyy AAnndd MMeettaabboolliissmm SUMMARY
What is energy?
What is the difference between potential energy and kinetic energy?
Laws of Thermodynamics
Energy and Metabolism
Redox reactions
Enzymes
Energy
Energy is the capacity to do work
Heat energy
Thermal energy flows from higher temperature to lower temperature.
Thermal energy causes particles to be in constant motion.
Heat energy cannot do cell work.
Energy: Potential and Kinetic
Potential energy
Kinetic energy
Energy Conversion
All forms of energy can be changed into other forms of energy.
Example: photosynthesis converts radiant energy to chemical energy.
Closed and Open Systems
Closed system
No energy exchange with surroundings – ex. battery driven motor
Open systems
Living organisms
Exchange energy with surroundings
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The First Law of Thermodynamics
Energy cannot be created or destroyed but can be transferred and changed in form.
Plants convert light energy into chemical energy stored in carbohydrates,
proteins and lipids.
Animals eat plants and convert the chemical energy in carbohydrates, etc. into
ATP.
The Second Law of Thermodynamics
Disorder (entropy) in the universe, a closed system, is continuously increasing.
No energy transfer is 100% efficient.
When energy is transferred to another form, some dissipates as heat. Heat
causes random motion of particles that contributes to entropy.
Reminder: heat energy cannot be used by cells for work.
Entropy is energy that causes disorder and cannot be used to do work.
Enthalpy is the potential energy in a system – example chemical bonds of a
molecule.
Free energy is available to do work.
Energy of Chemical Reactions
All chemical reactions involve changes in free energy.
Exergonic reactions
Endergonic reactions
Energy and Metabolism
Sum of all the chemical reactions in the cell or organism.
Catabolism
Decomposition of large complex molecules into smaller, simpler molecules;
exergonic reaction.
Anabolism
Synthesis of complex molecules from simpler molecules; endergonic
reaction.
ATP
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Most are proteins although there are some RNAs that have enzyme activity =
ribozymes.
Enzymes are specific for one or a few similar substances.
Active site –
**Lock and key analogy.
Enzyme-Substrate Complex
Reactants bind to enzyme’s active site forming enzyme–substrate complex.
The shapes of enzyme and substrate change and stresses chemical bonds.
How do they work?
*Create a site where reactants can come together = active site.
When reactants bind their chemical bonds are stressed and more easily broken.
*The weakening of the bonds lowers the Activation Energy = energy required to
start the chemical reaction.
Activation Energy
Enzymes lower activation energy (EA), the energy used to start a reaction.
How are Enzymes Regulated
Most enzymes are proteins and are subject to denaturation.
What denatures proteins?
Each enzyme has an optimal pH and temperature.
Because they participate in chemical reactions they are also regulated by:
Enzyme and Substrate Concentration Feedback Inhibition
An increase in product concentration causes the reaction to slow down.
End product inhibits earlier reaction in metabolic pathway.
Allosteric Enzymes
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Allosteric regulators
bind to allosteric sites (noncatalytic sites).
change enzyme’s activity usually by changing the shape of the active site.
Inhibition
Reversible inhibition
competitive (inhibitor competes with substrate for active site).
noncompetitive (inhibitor binds at a different site).
Irreversible inhibition
inhibitor combines with enzyme and permanently inactivates it. Example:
heavy metal poisoning.
