Chains of RNA are made of nucleotides.
Nucleotides are organic molecules that serve as the monomer units for forming the nucleic acid polymers deoxyribonucleic acid(DNA) and ribonucleic acid (RNA), both of which are essential biomolecules in all life-forms on Earth. Nucleotides are the building blocks of nucleic acids; they are composed of three subunit molecules: a nitrogenous base, a five-carbon sugar (ribose or deoxyribose), and at least one phosphate group. There are four types of nitrogenous bases in RNA. They are called: adenine, uracil, cytosine and guanine. The backbone atoms of a nucleotide can form strong chemical bonds with the backbone atoms of any other RNA nucleotide. This coupling is achieved by a OH group of a nucleotide, which has a lot of electrons around the oxygen, that wants to find something positive.Two of the electrons of that oxygen “attack” the phosphorus atom of another nucleotide. The result is that two nucleotides are attached to each other with a phosphodiester bond.
This bond connects the 3′ carbon of one nucleotide to the 5′ carbon of another nucleotide.Which nucleotides attach to each other is completely random, this means that different chains can have different sequences from left to right. The nitrogenous bases of nucleotides are attracted to other bases like a sort of magnet but they are selective about who they will stick to. Guanine selectively pairs with cytosine and adenine selectively pairs with uracil.
These nitrogenous bases are bound to each other by hydrogen bonds. This process is called base-pairing. With a little bit of assistance base pairing allows chains of RNA to replicate and evolve.
When a long chain of RNA is suspended in cool water with high concentrations of free nucleotides, the chain can act as a template for its own replication. Nucleotides automatically form pairs with their “partners” on the existing chain. If their backbone atoms form chemical bonds with each other ( researchers have not figured out how this bond was arrived without assistance in the wild) a complementary RNA strand is created. If the water is then heated, the hydrogen bonds between the bases are broken causing the two strands to disconnect from each other. Then the cycle can be repeated but this time with two strands acting as templates. There is a form of competition between the formed RNA fragments, where those who are able to reproduce themselves the best have a selective advantage. New chains of RNA can also be formed by the binding of small RNA fragments on the parent molecule.
An important property of RNA strands is their ability to form loops, where even bonds can be formed between the loops themselves. This results in a specific 3-dimensional structure:Thanks to this spatial structure RNA can exhibit enzymatic properties. RNA molecules with enzymatic activity are called ribosomes. Men suspects that such ribosomes have played an important role in the doubling of the RNA molecules. In 2005 it was proved that montmorillonite, a clay species that appeared in weathered volcanic ash, binds (small) RNA molecules and allows them to react with each other creating longer RNA chains. This process could also have occurred in the prebiotic times.
However, it is thought that before the appearance of RNA less complex molecules emerged. Possible candidates are threose nucleic acid (TNA) and peptide nucleic acid (PNA). In prebiotic conditions, these molecules could replicate spontaneously. Because of the random base sequences, it is likely that some fragments could replicate themselves easier than other fragments . So a molecular selection occurred.
Some fragments had simple catalytic properties, which had a positive impact on the reproduction. There were probably fragments between the evolving molecules that catalyzed the formation of new nucleotides, eventually resulting in the creation of RNA fragments.(How could these nucleotides have formed?, just give available info. In what kind of RNA-like molecules did they form?, mostly done)