* Note: We will soon see other important purines and pyrimidines.

   or pyrimidine-derived bases through an N-glycosidic linkage.

Thepyrimidine NSs end in "-dine" : cytidine, uridine, deoxythymidine

Time course of decomposition/hydrolysis of selected pyrimidine nucleotide derivatives in acidic solution and in the presence of cell membranes; stick representation of Figure A. This material is available free of charge via the Internet at .

Synthesis of Purine Ribonucleotides

Synthesis of Pyrimidine Ribonucleotides

The basic idea here is that there is exquisite control of the amounts ofpurine nucleotides available for synthesis of nucleic acids, and that thepathways are individually regulated at the cellular level. Furthermore, therelative amounts of ATP and GTP are also controlled at the cellular level.

Synthesis of Purine Ribonucleotides

looked at the diagrams in FA and UW again and again but I still don't quite understand the roles of in de novo purine synthesis.
Ordnerverwaltung für USMLE Step 1: Biochemistry other.

Synthesis of Pyrimidine Ribonucleotides


As building blocks for pyrimidine ribonucleotides, we have investigated the chemistry of glycolaldehyde 4, glyceraldehyde 5, cyanamide 6, cyanoacetylene 7, and phosphate—the same feedstock molecules ultimately invoked in the nucleobase ribosylation approach () (in ongoing work on the prebiotic synthesis of purine nucleotides, the systems chemistry of mixtures containing hydrogen cyanide, is additionally being investigated). However, we have not presumed a particular order of assembly, and have systematically investigated many options over the last decade or so (; ; ; ; , ). Furthermore, aware of the potential for certain molecules to act as catalysts of reactions in which other molecules are joined, an important aspect of our approach has been the study of the chemistry of multicomponent chemical systems, including mixed oxygenous and nitrogenous chemistry (). It has long been held in prebiotic chemistry that the aldol chemistry of aldehydes potentially required to make sugars should not be mixed with, for example, the oligomerization of hydrogen cyanide and cyanamide potentially required to make purine nucleobases (). This is because the two chemistries have been assumed to interfere with each other, suggesting the potential for a “combinatorial explosion” of minor by-products. However, given the impasse of preformed nucleobase ribosylation, and the conceptual difficulties with which a transition from a pre-RNA world to the RNA world is fraught, taking a few synthetic risks seemed justified.

Decrease de novo purine synthesis.

For cells that don’t excrete deoxyribonucleosides but instead degrade them further, that further degradation usually involves attack by nucleoside phosphorylases to yield deoxyribose-1-phosphate plus the free base. Further degradation of the purine and pyrimidine bases proceeds by pathways outlined in Purine ribonucleotide metabolism and Pyrimidine ribonucleotide metabolism.

b) Decrease de novo pyrimidine bio synthesis.

In conventional synthetic chemistry, the aforementioned difficulties in nucleobase ribosylation can be overcome with directing, blocking, and activating groups on the nucleobase and ribose (). Thus, the cytosine derivative 19 is directed to function as a nucleophile at N1 by alkylation of O2. The ribose-derived intermediate 20 is constrained to the furanose form by benzoylation of the C5-hydroxyl group, and neighboring group participation from an O2-benzoyl group directs β-glycosylation. These molecular interventions are synthetically ingenious, but serve to emphasize the enormous difficulties that must be overcome if ribonucleosides are to be efficiently produced by nucleobase ribosylation under prebiotically plausible conditions. This impasse has led most people to abandon the idea that RNA might have assembled abiotically, and has prompted a search for potential pre-RNA informational molecules (; ; ; ; ). However, we realized that there were other possible synthetic approaches that although less obvious, still had the potential to make the ribonucleotides 1 and 2 (). Furthermore, and as pointed out earlier, there are also alternative bond forming polymerization chemistries imaginable. Our plan was to work through these possibilities by systematic experimentation before deciding whether the abiogenesis of RNA is possible or not.