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Metabolism
The total of all reactions in a cell
Components of Metabolism
• Catabolism
• Breakdown of large molecules into smaller ones
• Energy is released
Components of Metabolism
• Anabolism
• Building of large molecules from smaller ones
• Energy is required
Energy Basics
• Two types—kinetic & potential
• Many forms—chemical, electromagnetic, mechanical, heat, nuclear
• Energy can be transformed from one type to another
1st Law of Thermodynamics
• Energy can be neither created nor destroyed but it can change forms
• Energy is conserved in a reaction
2nd Law of Thermodynamics
• Every energy transfer or transformation makes the universe more disordered.
• Entropy—The measure of the amount of disorder or randomness
Which has more entropy???
• A cluttered closet or a well-organized closet?
• An ice cube or a glass or water?
• A gallon of gasoline or the carbon dioxide and water vapor that escape the exhaust pipe?
There is an unstoppable trend toward randomization in nature
• Heat is a very disorganized form of energy and is the fate of all energy transformations.
• The quantity of energy in the universe is constant, but its quality is not.
Reactions that occur spontaneously
• Increase the stability of the system
• Increase the entropy (randomness or disorder) of the system
Spontaneous reactions
• Release energy that can perform work
• This energy is known as free energy
• It is represented by the letter G
Free energy is
• A measure of a system’s instability
• Systems that change to a more stable state have high free energy, low entropy or both.
The ATP molecule
• ATP is the energy currency for cellular work.
• Cells do the following kinds of work:
• Mechanical work
• Transport work
• Chemical work
The ATP molecule
• Is highly organized (low entropy)
• Very unstable (negative phosphates in close proximity)
• Therefore, has a very high free energy
• ΔG = -7.3 kcal/mol for hydrolysis of ATP
Free Energy and Equilibrium
• Equilibrium is point of maximum stability• At equilibrium ΔG = 0, there is no
change in the system• At equilibrium, cells are dead!• Cells must remain at disequilibrium
to continue to work
Exergonic reactions
• Release free energy
• ΔG is negative
• Occur spontaneously
• Can do work
• Respiration is an example
• ΔG for respiration = -686 kcal/mol
Endergonic Reactions
• Absorbs free energy
• ΔG is positive
• Do not occur spontaneously
• Photosynthesis is an example
• ΔG for photosynthesis is 686 kcal/mol
Analyze the ATP Cycle in terms of anabolism, catabolism,
endergoonic, exergonic, and free energy
How does ATP work?