ch 6

• Thermodynamics


  Branch of chemistry concerned with energy changes
• Cells are governed by the laws of physics and chemistry
• Energy


  Capacity to do work
• Two states of energy


  • Kinetic - energy of motion
  • Potential - stored energy
• Heat


  Most convenient way of measuring energy
• Calorie


  Heat required to raise 1 gram of water 1° C
• Calorie on food labels


  Actually a kilocalorie (1000 calories)
• Potential energy


  Energy required for the girl to climb to the top of the slide
• Kinetic energy


  Stored potential energy released as the girl slides down
• The Sun provides energy for most living systems
• Photosynthetic organisms


  Capture energy from sunlight and store it as potential energy in the covalent bonds between atoms in the sugar molecules
• Redox reactions


  Transfer electrons
• Oxidation


  Atom or molecule loses an electron
• Reduction


  Atom or molecule gains an electron, higher level of energy than oxidized form

  
• Oxidation-reduction reactions (redox) are always paired
• All activities of living organisms involve changes in energy
• First Law of Thermodynamics


  Energy cannot be created or destroyed, energy can only change from one form to another, total amount of energy in the universe remains constant
• Second Law of Thermodynamics


  Entropy (disorder) is continuously increasing, energy transformations proceed spontaneously to convert matter from a more ordered/less stable form to a less ordered/more stable form
• Free energy (G)


  Energy available to do work, G = H - TS (H = enthalpy, T = absolute temperature, S = entropy)
• Positive ΔG


  Products have more free energy than reactants, not spontaneous, requires input of energy, endergonic
• Negative ΔG


  Products have less free energy than reactants, spontaneous, exergonic
• Activation energy


  Extra energy required to destabilize existing bonds and initiate a chemical reaction
• Catalysts


  Substances that influence chemical bonds in a way that lowers activation energy, cannot violate laws of thermodynamics, do not alter the proportion of reactant turned into product

  
• ATP


  Adenosine triphosphate, primary energy "currency" used by cells, composed of ribose, adenine, and a chain of three phosphates, key to energy storage, bonds are unstable and release energy when broken

  
• ADP


  Adenosine diphosphate, two phosphates
• AMP


  Adenosine monophosphate, one phosphate, lowest energy form
• ATP hydrolysis


  Drives endergonic reactions, energy released can supply the energy needed by the endergonic reaction

  
• ATP not suitable for long-term energy storage, cells store only a few seconds worth of ATP</b>
• Most enzymes are proteins, some are RNA (ribozymes)
• Enzyme active site


  Pockets or clefts for substrate binding, forms enzyme-substrate complex, applies stress to distort particular bond to lower activation energy
• Multienzyme complexes


  Subunits work together to form molecular machine, offer advantages in catalytic efficiency
• Ribozymes


  RNA molecules that can catalyze reactions, can catalyze reactions on themselves (intramolecular) or on other molecules (intermolecular)

  
• Enzyme function


  Rate depends on concentrations of substrate and enzyme, affected by temperature and pH
• Competitive inhibitor


  Competes with substrate for binding to the enzyme
• Noncompetitive inhibitor


  Binds to enzyme at a site other than active site, does not necessarily affect substrate binding
• Allosteric enzymes


  Exist in active and inactive forms, allosteric inhibitors can bind to allosteric site and reduce enzyme activity
• Inhibitor


  Substance that binds to enzyme and decreases its activity
• Competitive inhibitor


  • Competes with substrate for binding to the enzyme (the inhibitor can but does not necessarily bind to the active site)
• Noncompetitive inhibitor


  • Binds to enzyme at a site other than active site
  • Does not necessarily affect substrate binding to enzyme
  • Inhibits enzymatic activity
• Allosteric inhibition is not always non-competitive; it can also be competitive and uncompetitive