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During the mid-to-late 1950s Crick was very much intellectually engaged in sorting out the mystery of how proteins are synthesised. By 1958, Crick's thinking had matured and he could list in an orderly way all of the key features of the protein synthesis process:
[7]
- genetic information stored in the sequence of DNA molecules
- a "messenger" RNA molecule to carry the instructions for making one protein to the cytoplasm
- adaptor molecules ("they might contain nucleotides") to match short sequences of nucleotides in the RNA messenger molecules to specific amino acids
- ribonucleic-protein complexes that catalyse the assembly of amino acids into proteins according to the messenger RNA
The adaptor molecules were eventually shown to be
tRNAs and the catalytic "ribonucleic-protein complexes" became known as
ribosomes. An important step was the realization by Crick and Brenner on 15 April 1960 during a conversation with
François Jacob that
messenger RNA was not the same thing as
ribosomal RNA.
[59] Later that summer, Brenner, Jacob, and
Matthew Meselson conducted an experiment which was the first to prove the existence of messenger RNA.
[59] None of this, however, answered the fundamental theoretical question of the exact nature of the genetic code. In his 1958 article, Crick speculated, as had others, that a triplet of nucleotides could code for an amino acid. Such a code might be "degenerate", with 4×4×4=64 possible triplets of the four nucleotide subunits while there were only 20 amino acids. Some amino acids might have multiple triplet codes. Crick also explored other codes in which, for various reasons, only some of the triplets were used, "magically" producing just the 20 needed combinations.
[60] Experimental results were needed; theory alone could not decide the nature of the code. Crick also used the term "
central dogma" to summarise an idea that implies that genetic information flow between macromolecules would be essentially one-way:
DNA → RNA → protein
https://en.wikipedia.org/wiki/Francis_Crick