Metabolism

• The living cell is a miniature chemical factory where thousands of reactions occur
• The cell extracts energy and applies energy to perform work
• Some organisms even convert energy to light, as in bioluminescence
• Metabolism


  The totality of an organism's chemical reactions
• Metabolism is an emergent property of life that arises from interactions between molecules within the cell
• Metabolic pathway


  1. Begins with a specific molecule and ends with a product

  2. Each step is catalyzed by a specific enzyme
• Catabolic pathways


  Release energy by breaking down complex molecules into simpler compounds
• Anabolic pathways


  Consume energy to build complex molecules from simpler ones
• Bioenergetics


  The study of how organisms manage their energy resources
• Kinetic energy


  Energy associated with motion
• Heat (thermal energy)


  Kinetic energy associated with random movement of atoms or molecules
• Potential energy


  Energy that matter possesses because of its location or structure
• Chemical energy


  Potential energy available for release in a chemical reaction
• Energy can be converted from one form to another
• Thermodynamics


  The study of energy transformations
• Closed system


  Isolated from its surroundings
• Open system


  Energy and matter can be transferred between the system and its surroundings
• Organisms are open systems
• First law of thermodynamics

  The energy of the universe is constant: Energy can be transferred and transformed, but it cannot be created or destroyed
• Second law of thermodynamics

  Every energy transfer or transformation increases the entropy (disorder) of the universe
• Living cells unavoidably convert organized forms of energy to heat
• Spontaneous processes occur without energy input; they can happen quickly or slowly
• For a process to occur without energy input, it must increase the entropy of the universe
• Cells create ordered structures from less ordered materials
• Organisms also replace ordered forms of matter and energy with less ordered forms
• Energy flows into an ecosystem in the form of light and exits in the form of heat
• The evolution of more complex organisms does not violate the second law of thermodynamics
• Entropy (disorder) may decrease in an organism, but the universe's total entropy increases
• Free energy


  Energy that can do work when temperature and pressure are uniform, as in a living cell
• Free-energy change (∆G)


  Related to the change in enthalpy (∆H), change in entropy (∆S), and temperature in Kelvin (T): ∆G = ∆H - T∆S
• Only processes with a negative ∆G are spontaneous
• Spontaneous processes can be harnessed to perform work
• Free energy


  A measure of a system's instability, its tendency to change to a more stable state
• During a spontaneous change, free energy decreases and the stability of a system increases
• Equilibrium


  A state of maximum stability
• A process is spontaneous and can perform work only when it is moving toward equilibrium
• Exergonic reaction


  Proceeds with a net release of free energy and is spontaneous
• Endergonic reaction


  Absorbs free energy from its surroundings and is nonspontaneous
• Reactions in a closed system eventually reach equilibrium and then do no work
• Cells are not in equilibrium; they are open systems experiencing a constant flow of materials