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CHAPTER 5 The Working Cell
Modules 5.1 – 5.4
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Cool “Fires” Attract Mates and Meals
Fireflies use light, instead of chemical signals, to send signals to potential mates Females can also use light flashes to attract males of other firefly species — as meals, not mates
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The light comes from a set of chemical reactions, the luciferin-luciferase system
Fireflies make light energy from chemical energy Life is dependent on energy conversions
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ENERGY AND THE CELL Living cells are compartmentalized by membranes Membranes are sites where chemical reactions can occur in an orderly manner Living cells process energy by means of enzyme-controlled chemical reactions
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5.1 Energy is the capacity to perform work
Energy is defined as the capacity to do work All organisms require energy to stay alive Energy makes change possible
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Kinetic energy is energy that is actually doing work
Figure 5.1A Potential energy is stored energy Figure 5.1B
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5.2 Two laws govern energy conversion
First law of thermodynamics Energy can be changed from one form to another However, energy cannot be created or destroyed Figure 5.2A
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Second law of thermodynamics
Energy changes are not 100% efficient Energy conversions increase disorder, or entropy Some energy is always lost as heat Figure 5.2B
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5.3 Chemical reactions either store or release energy
Cells carry out thousands of chemical reactions The sum of these reactions constitutes cellular metabolism
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Potential energy of molecules
There are two types of chemical reactions: Endergonic reactions absorb energy and yield products rich in potential energy Products Amount of energy INPUT Potential energy of molecules Reactants Figure 5.3A
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Amount of energy OUTPUT Potential energy of molecules
Exergonic reactions release energy and yield products that contain less potential energy than their reactants Reactants Amount of energy OUTPUT Potential energy of molecules Products Figure 5.3B
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5.4 ATP shuttles chemical energy within the cell
In cellular respiration, some energy is stored in ATP molecules ATP powers nearly all forms of cellular work ATP molecules are the key to energy coupling
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Adenosine triphosphate Adenosine diphosphate (ADP)
When the bond joining a phosphate group to the rest of an ATP molecule is broken by hydrolysis, the reaction supplies energy for cellular work Adenine Phosphate groups Hydrolysis Energy Ribose Adenosine triphosphate Adenosine diphosphate (ADP) Figure 5.4A
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Potential energy of molecules
How ATP powers cellular work Reactants Products Potential energy of molecules Protein Work Figure 5.4B
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Dehydration synthesis
The ATP cycle Hydrolysis Dehydration synthesis Energy from exergonic reactions Energy for endergonic reactions Figure 5.4C
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