Background vocabulary: monomer and polymer
Living things have genetic information stored in a polymer of DNA.
That info gets copied into polymers of RNA.
That is translated, with the help of mRNA, into polymers of proteins.
And each of these steps needs special enzymes.
Life in today’s cells, and even viruses, is wicked complicated.
Hard to imagine all it all evolved, all at once. But who says it had to do it all at once?
Maybe one simple kind of reaction developed, then later, other kinds of reactions, and then over a loooong period of time, even other types.
Life in the very beginning
Perhaps once upon a time, RNA was all that life had.
Pieces of RNA were both the genes and the catalyst.
e.g. RNA could do base pairing with itself, bend, and graph other molecules.
RNA sequences could be copied by other RNAs.
Only later did DNA and proteins evolve.
This is the idea of the RNA world
A hypothetical stage in the history of life on Earth
Idea – RNA developed before DNA and proteins developed.
Alexander Rich first proposed the concept in 1962
Growing amounts of evidence for this is strong enough that the hypothesis has gained wide acceptance.
How is RNA like DNA?
Both can store and replicate genetic information;
How is RNA like an enzyme?
Both can catalyze (start) chemical reactions.
Are any enzymes today made of RNA?
the ribosome is composed primarily of RNA.
Ribosomes are part of many important enzymes, such as Acetyl-CoA, NADH, etc.
So why does life depend on DNA replication nowadays?
DNA is more stable than RNA
What does RNA, and DNA, look like?
How would RNA monomers assemble into polymers?
How could copies be made?
So let us look at the possible in steps, in order.
At the far left is long ago… then an RNA based world of life developed… and later a DNA and protein based world of life developed.