Scientists Crack 40-year-old DNA Puzzle
In 1968, Marshall Nirenberg, Har Gobind Khorana and Robert Holley received a Nobel Prize for working out how proteins are produced from the genetic code. They discovered that three letter ‘words’ - known as codons - are read from the DNA code and then translated into one of 20 amino acids. These amino acids are then strung together in the order dictated by the DNA code and folded into complex shapes to form a specific protein.
As the DNA ‘alphabet’ contains four letters - called bases - there are as many as 64 three-letter words available in the DNA dictionary. This is because it is mathematically possible to produce 64 three-letter words from any combination of four letters.
But why there should be 64 words in the DNA dictionary which translate into just 20 amino acids, and why a process that is more complex than it needs to be should have evolved in the first place, has puzzled scientists for the last 40 years.
sciencedaily.com
The new theory builds on an original idea suggested by Francis Crick - one of the discoverers of the structure of DNA - that the three-letter code evolved from a simpler two-letter code, although Crick thought the difference in number was simply an accident “frozen in time”.
The University of Bath researchers suggest that the primordial ‘doublet’ code was read in threes - but with only either the first two ‘prefix’ or last two ‘suffix’ pairs of bases being actively read.
By combining arrangements of these doublet codes together, the scientists can replicate the table of amino acids - explaining why some amino acids can be translated from groups of 2, 4 or 6 codons. They can also show how the groups of water loving (hydrophilic) and water-hating (hydrophobic) amino acids emerge naturally in the table, evolving from overlapping ‘prefix’ and ‘suffix’ codons.
“When you evolve our theory for a doublet system into a triplet system, you get an exact match up with the number and range of amino acids we see today,” said Dr van den Elsen, who has worked with Dr Stefan Babgy and Huan-Lin Wu on the theory.
“This simple theory explains many unresolved features of the current genetic code. No one has ever been able to do this before, so we are very excited.” |
