Universality of the genetic code:
For several years it was thought in which the genetic code is universal, that is all living organisms used the similar code. Now we know that the genetic code is almost the similar in all organisms but there are a few variances. Mitochondria contain the DNA as double-stranded DNA circles and the mitochondrial genome codes for about 10-20 proteins. Amazingly, in mitochondrial mRNAs, some codons have several meanings from their counterparts in mRNA in the cytosol. A few instances are shown below N implies any of the four nucleotides G, C, U or A:
Some unicellular organisms are also now known to use a different genetic code. For instance:
