2018/04/06

RNA editing - more reasons why DNA doesn't determine traits

RNA editing - sophisticated mechanisms point to Design

http://www.biology-pages.info/R/RNA_Editing.html

Excerpt: "Occasionally researches encounter a gene with a sequence of nucleotides that does not match exactly that in its RNA product:
  • messenger RNA (mRNA) or
  • ribosomal RNA (rRNA) or
  • transfer RNA (tRNA) and even
  • microRNA (miRNA)
  • long non coding RNA (lncRNA)

If the product is mRNA, some of the codons in the open reading frame (ORF) of the gene specify different amino acids from those in the protein translated from the mRNA of the gene.

The reason is RNA editing: the alteration of the sequence of nucleotides in the RNA
  • after it has been transcribed from DNA but
  • before it is translated into protein

RNA editing occurs by two distinct mechanisms:
  • Substitution Editing: chemical alteration of individual nucleotides.These alterations are catalyzed by enzymes that recognize a specific target sequence of nucleotides (much like restriction enzymes):
    • cytidine deaminases that convert a C in the RNA to uracil (U);
    • adenosine deaminases that convert an A to inosine (I), which the ribosome translates as a G. Thus a CAG codon (for Gln) can be converted to a CGG codon (for Arg).
  • Insertion/Deletion Editing: insertion or deletion of nucleotides in the RNA.These alterations are mediated by guide RNA molecules that
    • base-pair as best they can with the RNA to be edited and
    • serve as a template for the addition (or removal) of nucleotides in the target"

       
My comment: DNA is just passive information library for the cell that has several clever ways to modify RNA products. RNA editing occurs before alternative splicing. I have collected a few valuable scientific facts about RNA-editing that help us understand the significance of RNA molecules:
  • Animal cells use an editing mechanism that converts adenosine residues to inosine residues (which masquerade as guanosine residues) in messenger RNA. (Masquerading technology points to extreme complexity of information handling.)
  • RNA editing generates post-transcriptional sequence alterations.
  • RNA editing can generate a multitude of transcript isoforms and can potentially be used to optimize protein function in response to varying conditions.
  • This has a biological significance in controlling the amount of functional RNA molecules in the cell, in expanding the functionality of a limited set of transcripts, and in defending the cell against certain RNA viruses.
  • More than half the amino acids of the genetic code can be altered in this fashion.There are at least 100 million adenosine-to-inosine RNA editing sites in human transcripts.
  • More than 140 types of chemical modifications have been found in RNA.
RNA products don't tolerate mutations. Even the slightest epigenetic errors are associated with serious diseases. That's why the theory of mutation driven evolution is the most serious heresy of our time. Don't get lost.