3. The Mobility of E* and Organization 



No form of energy can be mobile if there is nothing to conduct 

 it So if we are looking for mobile forms of energy which could 

 take part in biological energy transmissions we have to consider 

 not only the energy itself, but also the mechanisms which have to 

 conduct it. In this chapter I will review instances of mobility of 

 energy and discuss the qualities demanded of the medium, leaving 

 open the question of which of these mechanisms play a role in 

 living systems. That such transmissions do occur was shown by 

 photosynthesis in which many chlorophyll molecules collaborate in 

 the reduction of one CO2 molecule (Arnold and Meek) . 



CONJUGATED SYSTEMS, v ELECTRONS, AND n,7r TRANSITIONS 



If a molecule contains a system of conjugated double bonds, 

 then it also has w electrons — which are no longer bound to any ! 

 single atom but belong to the conjugated system as a whole, within I 

 which they have a more or less free mobility. If such a tt electron 

 accepts energy and is excited to a higher ir* energy level, then its 

 E* belongs to the whole conjugated system and may produce 

 changes at any of its points. The purine in ATP has such an ex-i 

 tensive conjugated system, and so have pyrimidins, isocyclic aro- 

 matic compounds, or carotenes with their long chain, built of 

 isoprene units. 



Biological catalysts and cofactors often contain N, O, or S atoms 

 in their conjugated system or linked to it. These atoms have their 

 "nonbonded" "lone pair" of electrons which can be excited to the 

 »• levels and thus contribute to the pool of ir* electrons. Those 

 so-called n,ir excitations discovered by McMurry and Mulliken, 

 have specific qualities: their lifetime is considerably longer than 



10 



