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Purine

physical science Maturity 11-13 Next article →

Purine is a heterocyclic aromatic organic compound. It is made of two rings fused together. These rings are called pyrimidine and imidazole.

purines
purines

Purines are the most common nitrogen-containing heterocycles in nature. They are water-soluble and belong to a wider class of molecules. These molecules include various substituted purines and their tautomers. A tautomer is a version of a molecule where a hydrogen atom moves to a different position. In purine, there are four such versions: 1-H, 3-H, 7-H, and 9-H.

Basicpurines
Basicpurines

The common crystalline form of purine favors the 7-H version. However, in polar solvents, the 9-H and 7-H versions are most common.

Inside living cells, purines serve as essential building blocks. They belong to a group called nitrogenous bases. The two main purine bases are adenine (A) and guanine (G). These bases attach to a sugar called ribose to form ribonucleosides. They can also attach to deoxyribose to form deoxyribonucleosides. When these nucleosides add phosphoric acid, they become nucleotides. These nucleotides, such as deoxyguanylate and deoxyadenylate, build DNA and RNA.

Purinesynthesis-en (cropped)
Purinesynthesis-en (cropped)

Purines also help in metabolic and signaling processes. They form important molecules like guanosine monophosphate (GMP) and adenosine monophosphate (AMP). They are also parts of ATP, GTP, cyclic AMP, NADH, and coenzyme A.

Cells must maintain a very strict balance of these molecules. Purines work alongside another group called pyrimidines. Both groups are self-inhibiting and self-activating. When a cell makes purines, the purines inhibit the enzymes that make more purines. At the same time, they activate the enzymes needed to make pyrimidines. Pyrimidines do the same thing for purines. This constant feedback loop ensures that cells have nearly equal amounts of both substances. Without this balance, cellular processes involving DNA and RNA could fail. Defects in the enzymes that control these levels may even increase cancer risks.

Dietary intake can significantly affect the levels of purines in the body. Purines are found in high concentrations in meat and seafood. Internal organs like the liver and kidney are especially rich in them. Examples include anchovies, sardines, monkfish, and shrimp. Certain foods are high in hypoxanthine, adenine, and guanine. These specific bases can lead to higher blood levels of uric acid. For instance, animal meats with more than 200 mg of hypoxanthine per 100 g increase uric acid levels.

TraubePurineSynthesis
TraubePurineSynthesis

Interestingly, some vegetables like spinach and peas have purines but do not raise uric acid levels. This might be due to how they are digested.

Scientists have a long history of studying these compounds. The name "purine" was created by German chemist Emil Fischer in 1884. He combined the Latin words "purum" and "uricum." Fischer successfully synthesized purine for the first time in 1898. He started with uric acid, which Carl Wilhelm Scheele had isolated from kidney stones in 1776.

FischerPurineSynthesis-crop
FischerPurineSynthesis-crop

Fischer's process involved reacting uric acid with PCl5 to create 2,6,8-trichloropurine. He then converted this into 2,6-diiodopurine using HI and PH4I. Finally, he used zinc dust to reduce the product into purine.

Purines are vital to all known life on Earth. They are found in eukaryotes, bacteria, and archaea. This shows how essential they are for biological survival. Most species can perform de novo biosynthesis, which is building purines from scratch. A study of 65 archaeal species found that 58 had a nearly complete set of genes for this. However, seven species lacked these genes entirely. These species must acquire purines from their environment to grow. This makes them similar to certain fungus mutants in laboratory studies.

Understanding purines also helps us explore the origins of life. Researchers study how these molecules might have formed before life existed. For example, four HCN molecules can join to form diaminomaleodinitrile. This can eventually turn into almost all natural purines. In 1961 and 1966, scientists showed how these chemical pathways might work. Other studies have shown that purine bases can join with ribose in water droplets. This step is a key part of how RNA might have formed on early Earth. This connection between simple chemistry and complex life remains a major area of science.

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File:Purinesynthesis-en (cropped).svg
Purinesynthesis-en (cropped).svg
File:Basicpurines.png
Basicpurines.png
File:TraubePurineSynthesis.svg
TraubePurineSynthesis.svg
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