The first cells which appeared on Earth, in conclusion, had high molecular weight protoribosomes, a mixture of ribozymes and protein enzymes, and RNA genomes. They truly were ribocells, and their appearence marked, to all effects, the origin of life.

The genetic code

Genes can replicate and transmit their information to other genes, but proteins cannot. The information of an amino acids chain is always coming from the information of a nucleotide sequence carried by a messenger RNA, and in this process an amino acid is always specified by a group of three nucleotides that is called a codon.
The messenger RNAs can be regarded therefore as ideally divided in nucleotide triplets, and since the combinations of 4 nucleotides in groups of 3 are 64 (43), there can be a total of 64 codons for 20 amino acids. The rules of correspondence between the 20 natural amino acids and the 64 codons represent, collectively, the genetic code (Figure 5-7).
As we can see from the figure, three codons are used as protein synthesis termination signals, while the other 61 specify the amino acids and the initiation signal. Between 61 codons and 20 amino acids there cannot be a one-to-one correspondence, and in fact some amino acids are specified by 6 codons, some by 4, others by 2, and only 2 amino acids are coded by a single codon. In technical terms, this is expressed by saying that the genetic code is degenerate.
The biological meaning of this degeneration is one of the few properties of the genetic code for which we do have a rational explanation. The degeneration could have been avoided by choosing, for example, 20 codons for 20 amino acids, 3 termination codons, and 61 nonsense codons. In this case, however, the chance mutation of a nucleotide would have produced in most cases a nonsense codon, and this would have interrupted protein synthesis. The great majority of mutations would not be expressed, and this explains why it is imperative that all 64 codons have a meaning. The degeneration of the genetic code, in short, is necessary to ensure the expression not only of genes but also of all their possible mutations.