Ribonucleotide
[2] Both types of pentoses in DNA and RNA are in their β-furanose (closed five-membered ring) form and they define the identity of a nucleic acid.
Some examples include hypoxanthine, dihydrouracil, methylated forms of uracil, cytosine, and guanine, as well as modified nucleoside pseudouridine.
[7] Both DNA and RNA are built from nucleoside phosphates, also known as mononucleotide monomers, which are thermodynamically less likely to combine than amino acids.
The precursors for RNA are GTP, CTP, UTP and ATP, which is a major source of energy in group-transfer reactions.
Ribonucleotide reductase (RNR) is an essential enzyme for all living organisms since it is responsible for the last step in the synthesis of the four deoxyribonucleotides (dNTPs) necessary for DNA replication and repair.
Once dATP binds to ribonucleotide reductase, the overall catalytic activity of the enzyme decreases, as it signifies an abundance of deoxyribonucleotides.
It has been shown that the active sites of Y-family DNA polymerases are responsible for maintaining a high selectivity against ribonucleotides.
[13] Most DNA polymerases are also equipped to exclude ribonucleotides from their active site through a bulky side chain residue that can sterically block the 2'-hydroxyl group of the ribose ring.
In the case of the de novo pathway, both purines and pyrimidines are synthesized from components derived from precursors of amino acids, ribose-5-phosphates, CO2, and NH3.
Utilizing the five-ring sugar structure as a base, the purine ring is built a few atoms at a time in an eleven-step process that leads to the formation of inosinate (IMP).
Continuing down the pathway, the removal of the carbon skeleton of aspartate by SAICAR lyase results in 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR).
The formation of the pyrimidine ring begins with the conversion of Aspartate to N-Carbamoylaspartate by undergoing a condensation reaction with carbamoyl phosphate.
RNA is composed of purine and pyrimidine nucleotides, both of which are necessary for reliable information transfer, and thus Darwinian natural selection and evolution.
[18] The starting materials for the synthesis (cyanamide, cyanoacetylene, glycolaldehyde, glyceraldehyde and inorganic phosphate) were considered to be plausible prebiotic feedstock molecules.
[18] Nam et al. demonstrated the direct condensation of nucleobases with ribose to give ribonucleosides in aqueous microdroplets, a key step leading to RNA formation.
[19] Also, a plausible prebiotic process for synthesizing pyrimidine and purine ribonucleotides using wet-dry cycles was presented by Becker et al.[20] Prior to James Watson and Francis Crick's landmark paper that detailed the structure of DNA from Rosalind Franklin's X-ray crystallography image, there were several historical scientists that also contributed to its discovery.
[21] Friedrich Miescher, a Swiss physician, who, in 1869, was first to isolate and identify nucleic substance from the nuclei of white blood cells he later called "nuclein", paving the way for the discovery of DNA.
[22] Following Mieschers work, was the German biochemist, Albrecht Kossel, who, in 1878, isolated the non-protein components of "nuclein", and discovered the five nucleobases present in nucleic acids: adenine, cytosine, guanine, thymine and uracil.
[23] Although some fundamental facts were known about nucleic acids due to these early discoveries, its structure and function remained a mystery.
Eventually, Levene was able to identify the correct order of which the components of RNA and DNA are put together, a phosphate-sugar-base unit, in which he later called a nucleotide.
