Polymerization of Nucleotides
Once the concentration of RNA
nucleotides had reached a certain level, polymerization took place, and
a single strand of RNA polymer was formed on prebiotic Earth. The
sequential steps of the polymerization process are as follows [12]:
Step 1: Two nucleotides join together and form a dimer. The dimer is
adsorbed and properly aligned on a clay mineral which acts as a catalyst
and lowers the activation energy for polymerization.
Step 2: Although polymerization normally proceeds by joining third
nucleotide at an end of the dimer resulting in a trimer, due to a unique
structure of the nucleotides, the process differently proceeds by
bonding the base of third nucleotide with a complementary base of the
dimer first because this bonding does not need to overcome an activation
energy and occurs instantaneously when the two bases come to close each
other.
Step 3: Next, fourth nucleotide with base which is complementary to the
remaining unbonded base of the dimer is bonded and then third and fourth
nucleotides join. As a result, a double strand dimer is formed.
Step 4: The wet & dry cycle of environment causes breaking up of
hydrogen bond between the bases and the dimer and its complimentary
dimer are separated. The
complemental self-replication of the dimer is completed.
Step 5: The process independently continues further on each of the two
separated dimers and the number of the replicated dimer that is more
stable increases.
Step 6: Although the self-replication reaction dominates, as the number
of replicated dimers increases, there is a chance of polymerization
process by which a nucleotide joins at an end of one of the dimers
resulting in formation of a trimer (there is a small chance of formation
of a tetramer by joining two dimers together). If the trimer (or
tetramer) is more stable than the dimers, the self-replication of the
trimer starts. Bonding of free complementary nucleotides starts from one
end of the trimer and finishes at the other end, forming a double strand
trimer.
Step 7: The trimer and its complementary trimer are separated by the wet
& dry cycle. The self-replication of the trimer is completed.
The process continues and the length of the longest polymer steadily
increases as long as the free nucleotides are available. Growth of the
length reaches a limit when the dissociation rate of the polymer exceeds
the self-replication rate.