Thursday, 8 January 2015

Origin Of Life In RNA And Ribosomes, Not Selfish DNA

Evolution may have been driven by “selfish” ribosomes rather than “selfish” genes, a new assessment in the Journal of Theoretical Biology claims. Father-daughter duo Dr Robert and Dr Meredith Root-Bernstein argue in their paper that ribosomes, RNA structures in cells that assemble proteins, are the selfish driving force behind the origins of life in the last universal common ancestor.

[caption id="attachment_173" align="alignleft" width="590"]"See DNA. See DNA run. Run, DNA, run!" - After every PCR at the electrophoresis machine. DNA and component nucleotides (left) sit in coiled double-helix beside single stranded RNA with its nucleotides. Image credit: Zappys Technology Solutions.[/caption]

Previous theories on evolution have focused on DNA, the molecule containing the genes or blueprints for life, and its replication. Ribosomes, however, are made from RNA – ribosomal RNA (rRNA) encrusted in stabilising proteins – which acts as a machine with transfer RNA (tRNA) and messenger RNA (mRNA) to read genetic information and assemble proteins.

Speaking about their theory, Dr Meredith asks “What does DNA want?” Previous theories suggested that DNA wants to replicate itself, but Dr Meredith found that DNA’s knotted resting state was against replication. Ribosomes on the other hand have a resting state ready to assemble proteins from mRNA ripped from DNA, and thus have a vested interest in seeing DNA replicated.

The reason RNA makes sense to the Drs Root-Bernstein as the origin and driving force behind evolution is because DNA is just too stubborn in its coiled state. This is why mRNA is used as the go-between for DNA and protein assembly; RNA is simply easier to read. The flipside is that RNA has a short lifespan without protective proteins, so is not as ideal as DNA for long-term storage of genetic information. To put it another way, DNA is the Read Only Memory and RNA is the Random Access Memory for genetic information.

The Dr Root-Bernstein team discovered that vestigial genetic information exists in ribosomal RNA, which is conserved in all living cells playing the same structural role in protein assembly. This genetic information seems to code for the associated mRNA and tRNAs necessary to for the ribosome to self-replicate, suggesting that ribosomes themselves are responsible for life’s origins.

This discovery may seem a blow to the “selfish gene” theory of evolution, refined and popularised by Dr Richard Dawkins, though it may not be the case. So-called “selfish” gene-driven evolutionary theory doesn’t purport to be about the origins of life, merely the adaptation of it. With the advent of life’s use of DNA as the "hard drive" for genetic information, and as ribosomes took on a more passive role in the early cell, “selfish” genes could then dictate the course of life's adaptation through evolution as we understand it today.

No comments:

Post a Comment