97 



but these variations were not clearly related to the code. Similarly, 

 studies have shown a differential uptake of nucleotides and amino 

 acids into detergent droplets called micelles, but code-related correla- 

 tions were not evident from this work either. In 1976 the first 

 clear-cut, code-related correlations between hydrophilic (water 

 loving) and hydrophobic (water hating) properties of amino acids 

 and nucleotides were reported. In addition, other researchers showed 

 that a number of additional properties, including hydrophobicity, 

 polarity, and bulkiness were also correlated between amino acids and 

 nucleotides. Thus, very weak interactions can be detected between 

 amino acids and nucleotides, but whether these interactions provide 

 enough selectivity for a translation process is not yet clear. 



The demonstration of a weak, specific interaction between an 

 amino acid and a nucleotide does not put us much farther forward 

 unless we can couple it to an efficient peptide synthesis reaction. 

 Many mechanisms have been proposed for simple systems that might 

 be capable of translating nucleic acid sequences into peptides of pro- 

 tein sequences, but no experiment has ever shown actual translation 

 in the absence of the complex components of the contemporary cell. 

 A few experiments have shown a slight influence of nucleic acid on 

 the yield of condensation of a single amino acid, with variation of 

 yield as either the amino acid or nucleic acid is changed, but these 

 experiments are not convincing evidence of a translation effect. As a 

 result further experimental verification is in order. 



There is no paucity of suggestions for the origin of protein 

 synthesis and of the genetic code, but there are few suggestions that 

 are both chemically explicit and believable. Some papers are rather 

 philosophical and do not lead immediately to a testable experiment. 

 Others are explicit but the chemistry appears to be inconsistent with 

 present knowledge. Actually the requirements of an efficient peptide 

 synthesis system can be stated quite simply. The reacting amino 

 acids, perhaps attached to specific oligonucleotide carriers, need to 

 be lined up on the template, such that adjacent amino acids are held 

 close enough together and in the proper orientation to allow reac- 

 tion. The amino acids need to be in a sufficiently reactive form, so 

 that the peptide bond formation is a spontaneous reaction, but not 

 so reactive that hydrolysis competes with peptide bond formation. 

 In addition, the mechanism has to be recursive, i.e., repetition of the 

 process should result in a gradual elongation of the peptide chain. 



