L2

• Steady-state


  A state in which the characteristic composition of an organism changes little through time, but the population of molecules within the organism is in constant flux

  
• Equilibrium


  A state in which the rate of product formation exactly equals the rate at which product is converted to reactant, resulting in no net change in the concentration of reactants and products
• System


  All the reactants and products present, the solvent that contains them, and the immediate atmosphere - everything within a defined region of space
• Isolated system


  A system that exchanges neither matter nor energy with its surroundings
• Closed system


  A system that exchanges energy but not matter with its surroundings
• Open system


  A system that exchanges both energy and matter with its surroundings
• Entropy


  The randomness or disorder of the components of a chemical system
• Catabolism - Anabolism - Metabolism

  • Catabolism: breakdown of complex molecules
  • Anabolism: synthesis of complex molecules
  • Metabolism: all chemical reactions in a cell

  
• Free energy content


  The potential energy of a compound, related to the kind and number of its bonds
• Enthalpy


  The number and kinds of bonds in a compound
• Endergonic


  A process that requires the input of free energy
• Exergonic


  A process that releases free energy
• Enzymes


  Biological catalysts that increase the rate of chemical reactions without being consumed or permanently altered
• Transition State


  An unstable, high-energy intermediate state that forms during a chemical reaction
• Activation Energy


  The minimum energy required to start a chemical reaction
• Pathway


  A series of connected chemical reactions
• Feedback Inhibition


  The inhibition of an enzyme by the end product of the pathway it catalyzes
• Living cells and organisms must perform work to stay alive and reproduce
• Synthetic reactions within cells require the input of energy
• Cells have developed efficient mechanisms for coupling energy from sunlight or fuels to energy-consuming processes
• Cellular energy conversions can be considered in the context of the laws of thermodynamics
• The molecules and ions within a living organism differ in kind and concentration from those in the organism's surroundings
• Small molecules, macromolecules, and supramolecular complexes are continuously synthesized and broken down in a constant flux of mass and energy through the system
• The constancy of concentration in a living organism is the result of a dynamic steady state, far from equilibrium
• Maintaining the steady state requires the constant investment of energy; when the cell can no longer generate energy, it dies and begins to decay toward equilibrium
• Equilibrium is a state where the rate of product formation equals the rate of product conversion to reactant, resulting in no net change
• Steady state is a state where the characteristic composition changes little, but the population of molecules is in constant flux

  
• Living organisms are open systems that exchange both matter and energy with their surroundings
• Living organisms derive energy by oxidizing chemical fuels from the environment or by absorbing sunlight
• The first law of thermodynamics states that the total amount of energy in the universe remains constant, although the form may change
• Cells are capable of interconverting chemical, electromagnetic, mechanical, and osmotic energy with great efficiency
• Photosynthetic cells absorb light energy and use it to drive electrons from water to carbon dioxide, forming energy-rich products

  
• Nonphotosynthetic cells obtain energy by oxidizing the products of photosynthesis and passing electrons to atmospheric oxygen
• All energy transductions in cells can be traced to the flow of electrons from higher to lower electrochemical potential
• Oxidation-reduction reactions involve the loss and gain of electrons by reactants

  
• Forming informational macromolecules like DNA, RNA, and proteins requires the investment of energy to order the subunits in the correct sequence

  
• According to the second law of thermodynamics, the tendency in nature is toward ever-greater disorder or entropy in the universe
• Free energy must be supplied to a cell to bring about the synthesis of macromolecules from monomers
• Gibbs Free Energy


  A measure of the free-energy content of a system, defined in terms of enthalpy, entropy, and absolute temperature
• A process tends to occur spontaneously only if the free energy difference is negative