The Origin of Life 15 



duced and are responsible for the variation that permits evolution. 

 DNA molecules are chains made up of four nucleotide units: 

 deoxyguanylic acid, deoxycytidylic acid, deoxyadenylic acid, and 

 deoxythymidylic acid. Similarly, RNA molecules are made up of 

 four nucleotides: guanylic, cytidyhc, adenylic, and uridylic acids. 

 Each nucleotide group consists of a pentose sugar molecule with an 

 attached base and an attached phosphate group. The backbones of 

 the DNx\ and RNA molecules are made up of the pentose sugars 

 linked by the phosphate groups. Attached to each sugar residue in 



Fig. 1.3 1 Mechanical computer model for the production (by feedback) 

 of ordered sequences. The beam of the balance operates the gate 

 permitting an A ball to enter when the pans are balanced and a B ball 

 to enter when the pans are unbalanced. A balls are heavier than B 

 balls. (From Pattee, 1961, Biophysical Journal 1.) 



Sequence generated by the balance mechanism 



BBABAABABBAAABBABBBBABBABABBABBAABAAB 



A A A B B B A 



A B B B B A A 



B A B A B A A 



B B A B A B B 



B A B B B A A 



A B A A A A A 



BABBBBBAABABA 

 BAAAABBAAAAAB 



AAA 



ABA 



BBAABBBA 



ABBAABAA 



BBABAAAB 



ABBBBBBB 



BBBAABBABAAABA 

 AAAAAABBBBBBBA 

 BBBABAABABBAAABBABBBBA 

 BAAABBBAAAABABBBBBAABA 

 AA BBBBAAABABAAAABBAAAA 

 ABABABAABBAABBBABBBABA 



-(m(^ 



