Self And The Phenomenon Of Life: A Biologist Examines Life From Molecules To Humanity

Self and the Beginning of Life 39

“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

were obtained by reacting formaldehyde. The same author also identified
a number of amino acids as reaction products of hydrogen cyanide, amm-
onia and water: glycine, alanine, aspartic acid, serine, glutamic acid, threo-
nine, leucine, isoleucine, arginine, with the first four predominating.^20

3.7 Issue Number One: Which Came First?

This is a classic chicken-or-the-egg problem. There are three main mac-
romolecular players that are considered of prime importance in a cell:
DNA, RNA and protein. We also know that in a modern cell, the direc-
tion of information flow is from DNA to protein through RNA as an
intermediary, but not the reverse. But this probably was not the case in
the beginning of life. Though important as a depository of information,
none of the functions of DNA (replication and information transfer) can
happen without the aid of protein enzymes. The current consensus is
that DNA probably was not the first macromolecule in the genesis of
life. The choice then turns into RNA versus protein. Over the past few
decades, attention has been focused on RNA as the choice candidate
because of the discovery of “ribozymes,” a type of RNA molecules that
possesses enzyme (catalytic) activity.^21 This leads to the attractive possi-
bility that RNA can both be the information carrier and the workhorse
(enzymes) at the same time, before the advent of protein and DNA.
A  hypothesis of “RNA World” was proposed suggesting that there was
an era in early life during which RNA “ruled the world.” In this scenario,
RNA becomes both the chicken and the egg.^22 In the following sections
I shall evaluate the strengths and weaknesses of this theory.

3.8 Evidence in Favor of an RNA-first Scenario

These are the reasons supporting an ancient RNA World:

(1) RNA undergoes base pairing as does DNA, a prerequisite for
template replication.
(2) Unlike DNA, which forms a rigid double-helix structure in a pre-
dictable manner, an RNA chain can fold upon itself by intra-chain