104 Information Storage and Neural Control 



T-RNA molecules have a molecular weight of about 25 to 

 30,000 (80 to 100 nucleotide chain length). The sedimentation 

 constant of T-RNA is about 4S. Three additional characteristics 

 are of interest: 1) It has been shown that guanine mononucleotide 

 terminates one end of the T-RNA chain, 2) cytidylic acid- 

 cytidylic acid-adenylic acid is the trinucleotide which terminates 

 the other end of the T-RNA chain, and 3) each T-RNA chain 

 contains an unusual mononucleotide, pseudouridylic acid (PsU). 

 The function of pseudouridylic acid is unknown. An amino acid 

 can be attached to the adenylic acid end of the chain as shown 

 schematically in Equations 7 through 9 (30): 



[7] Amino acid + ATP — ^ Adenyl ~ Amino acid + Pyro- 

 phosphate 



[8] Adenyl « Amino acid + G- — PsU— -C-C-A -^ 



(T-RNA) 



Adenylic acid + G PsU C-C-A « Amino acid 



(T-RNA with activated amino acid) 



[9] T-RNA « Amino acid + Ribosomes -^ T-RNA + 

 Ribosomes (Amino Acid) 



Transfer-RNA comprises approximately 10 per cent of the total 

 cellular RNA. The mononucleotide content of the T-RNA from 

 a number of different sources has been determined (Table X). 

 T-RNA molecules from all sources have a high content of guanine 

 and cytosine (53-61 molar per cent (G + C)). 



TABLE X 



% (G + C) Content of Transfer — RNA 



