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.