3.4 Food as Fuel

• what do glucose and octane have in common?

  • both are good fuels possessing a great deal of potential energy due to many carbon-hydrogen bonds
  • but gram for gram, fats provide more energy than carbohydrates due to more numerous carbon-hydrogen bonds
  • fats are mostly hydrocarbon with carbon-carbon and carbon-hydrogen bonds
  • sugars contain stronger carbon-oxygen bonds and stronger bonds have lower energy electrons
• what influences potential energy of an electron?
• what influences potential energy of an electron?

  1. position and proximity to nucleus - electrons at higher energy levels contain more potential energy
  2. size of nucleus - electrons are more attracted to a larger nucleus (eg. molecules with lots of oxygen contain less potential energy due to its high electronegativity and therefore greater attraction for additional electron, as electrons are attracted they lost potential energy as energy is released in bond formation)
• oxidation of fuel molecules releases potential energy stored in molecules
• what are redox reactions? (occur together)

  • oxidation - losing electrons (removal of H atom/addition of O atom)
  • reduction - gaining electrons (removal of O atom/addition of H atom)
• in CH4 + 2 O2 => CO2 + energy + 2 H2O why is carbon oxidized?


  electrons from CH4 are more attracted to oxygen as Carbon has partially lost its shared electron in the reactions
• in CH4 + 2 O2 => CO2 + energy + 2 H2O why does oxygen become reduced?


  H2O molecule electrons are closer to oxygen, therefore oxygen gains electron
• combustion of fuels releases a lot of energy because the electrons of the carbon-hydrogen bonds move closer to electronegative oxygen atoms, moving closer to a larger nucleus which releases its energy
• what does cellular respiration and the combustion of butane have in common?

  • other than their fuel source, they're essentially the same reaction
  • the combustion reaction describes the overall process that occurs inside a cell, though this process is broken down into smaller steps
  • energy contained in bonds of glucose are released in small bursts, some are lost as heat and other energy keeps cell's metabolism running
• what is controlled oxidation?

  • captures more free energy, produces less waste thermal energy and the energy released can be harnessed
  • electron removed from glucose in pairs, not all at once - electrons transferred to electron carriers
  • electron carriers deposit electrons in ETC where they are moved from one complex to the next, ultimately allowing energy to be captured
• what is rapid combustion?

  • energy released at once and cannot be efficiently harnessed to drive metabolic reactions - in essence, no reaction is endothermic enough to absorb the energy released
• in both rapid combustion and controlled oxidation have identical net energy change (delta G) and both are exergonic - energy is released to surroundings