Every new biological discovery opens the door to a world of undreamed of miracles.
Back when Rosalind Franklin elucidated the structure of DNA and Francis Crick and James Watson figured out how DNA genes might work, no one really knew much about RNA. Gradually researchers discovered that a molecule christened “messenger RNA” (mRNA) transcribed genes from DNA. Two other types of RNA then translated the mRNA into proteins.
And what was the purpose of these proteins? In plants, animals, fungi, and various single-celled organisms, some proteins form rigid or moving structures, some provide storage or transport, some fight off infection, and some proteins catalyze the myriad chemical reactions that keep cells alive and doing their jobs.
So genes turned out to build organisms and run them by this method: DNA makes RNA, and RNA makes protein.
But this was just the tip of the iceberg.
For instance, when DNA makes RNA, and RNA makes protein, each step of this process is engineered by proteins (enzymes). Yet each protein was translated from genes (DNA). And the genes got transcribed and translated by RNA. So biologists began thinking that these molecules and this process couldn’t have sprouted from nothing. Something had to come first. Was it the DNA? The RNA? The protein?
Whatever came first had to have two functions. It had to be able to store the plans for each living organism—genes do this. And it had to be able to catalyze biochemical reactions in cells—enzymes do this.
At last, Nobel Prize winners Thomas R Cech and Sidney Altman came upon RNA enzymes that could do both the job of a gene and the job of an enzyme. Such a molecule was dubbed a “ribozyme.” Ribozymes may well be the ancestors of both DNA and enzymes made of protein. After the first ribozymes made it possible for successful cells, or perhaps mere successful molecules, to be duplicated, how might DNA and proteins have come about?
Even today, there are RNA viruses whose RNA gets “back-copied” into DNA. Perhaps the first DNA came about in such a way. And even today many ribozymes join with proteins to modify their catalytic activity. Perhaps the first protein enzymes came about in such a way. It’s exciting to imagine such molecular evolutions happening billions of years ago.
But RNA turns out to have many talents: More on this in my next post.