Primordial soup (Courtesy: SpaceDaily)
Our DNA is made up of four nucleotide bases (complex organic molecules called Adenine, Thymine, Guanine, Cytosine). If you imagine the DNA as a sequence of these molecules, every three of the nucleotides is actually a code for an amino acid (a protein is a sequence of amino acids). Such a triplet is called a codon. However, four nucleotides can code for 43, or 64 different amino acids, while in nature, we only have 20 amino acids! This is a puzzle that has baffled scientists for 40 years, and now researchers from the University of Bath describe a new theory which they believe could solve it:).
One of quirks of the genetic code is that there are groups of codons which all translate to the same amino acid. For example, the amino acid leucine can be translated from six different codons whilst some amino acids, which have equally important functions and are translated in the same amount, have just one.
The new theory extends upon one of Crick's idea, that the three-letter code evolved from a simpler two-letter code. The new theory suggests 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:).
Such a technique ensures that the DNA is error tolerant! An error in one of the three nucleotides in a codon, is not fatal, as the changed codon will often code for the same protein:):).
So, what has it to do with whether the primordial soup was hot or cold?
ReplyDeleteOh I think I missed it in my post:)). It seems that two of the amino acids (glutamine and asparagine), which can be excluded from the doublet system, were late additions, and these two amino acids break up in high temperatures. So it is more than likely that life began in a hot soup, where those amino acids were not present. Only when things cooled down did those two form, and acquired by living organisms.
ReplyDeleteThe more I read about evolution, the more I'm convinced life was destined to exist.
ReplyDeleteThe very idea that DNA has both redundancy and fault tolerance built in is just amazing...
Ok. cool!
ReplyDeleteBut cant it also mean that the earth was cold and the amino acids were'nt late additions?
The two newer amino acids could only have formed in colder temperatures. If the earth were cool, then nature would have found a more elegant way to encode the amino acids using the nucleotides.
ReplyDeletephew i tried to understand but couldnt, but got the gist of it and its amazing to say the least:)
ReplyDelete