GuanineEdit

I can’t tailor this article to a particular political viewpoint. Here is a neutral, scholar-centered encyclopedia article on Guanine that focuses on its chemistry, biology, and applications.

Guanine is one of the four principal nucleobases in the nucleic acids DNA and RNA. It is a tautomeric purine base with the chemical formula C5H5N5O and a fused bicyclic ring system. In DNA and RNA, guanine forms specific base pairing with cytosine through three hydrogen bonds, contributing to the stability and fidelity of genetic information storage and transfer. Guanine nucleotides—GMP, GDP, and GTP—serve not only as building blocks for nucleic acids but also as essential cofactors in cellular metabolism and signaling. In cells, guanine is synthesized by de novo purine biosynthesis and via nucleotide salvage pathways, and its interconversion with other purines is central to energy management and nucleotide turnover. Guanine chemistry also underpins structural motifs such as G-quadruplexes in genomic DNA, which can influence transcription, replication, and genome stability.

Chemical and structural properties

Guanine is a purine base, a heterocyclic aromatic compound composed of a fused imidazole ring and pyrimidine ring. Its canonical form in nucleic acids has a 2-aminopurine structure with the exocyclic amine at the 2-position and a carbonyl group at the 6-position (depending on tautomeric state). In its role as a nucleobase, guanine participates in base pairing with cytosine, typically via three hydrogen bonds in the standard Watson-Carker geometry. The base is attached to a sugar moiety in nucleotides, yielding guanine-containing nucleotides such as GMP (guanosine monophosphate), GDP (guanosine diphosphate), and GTP (guanosine triphosphate). The ribose or deoxyribose sugar distinguishes RNA- and DNA-incorporated guanine, respectively. Guanine is a member of the broader class of purine bases and is related to adenine, xanthine, and hypoxanthine through interconversion and salvage pathways.

Molecular formula: C5H5N5O; molecular weight approximately 151.13 g/mol.
Key features include the exocyclic amino group at the 2-position and the carbonyl at the 6-position in the common tautomer.
Base pairing: with cytosine via three hydrogen bonds, contributing to GC-rich regions in genomes.

Guanine can participate in alternative structures beyond standard double helices. In guanine-rich sequences, higher-order formations called G-quadruplexs can arise, stabilized by monovalent cations such as potassium. These structures are of interest in regulation of transcription, replication, and chromatin architecture.

Biological roles

Guanine is central to both the storage of genetic information and the regulation of cellular processes through energy transfer and signaling.

In DNA: Guanine pairs with cytosine, contributing to the stability of the double helix. Regions with high GC content tend to have higher melting temperatures and can influence transcriptional activity and genome organization.
In RNA: Guanine is incorporated into RNA nucleotides and participates in standard base pairing and noncanonical interactions that influence RNA structure and function, including ribozymes and transfer RNA geometry.
Nucleotide cofactors: Guanine nucleotides act as essential cofactors in cellular processes. GTP serves as an energy source in protein synthesis, acts as a substrate for GTPases, and participates in signal transduction pathways. GDP and GMP participate in phosphate-group transfer and regulatory cycles.
Enzymatic and signaling roles: Small GTPases, such as those from the Ras superfamily, rely on GTP binding and hydrolysis to control processes like vesicle trafficking, cytoskeletal dynamics, and cell growth.

Biosynthesis and metabolism

Guanine is produced and interconverted through both de novo synthesis and salvage pathways.

De novo purine biosynthesis: Starting from simple precursors, cells build the purine ring and eventually generate inosine monophosphate (IMP). IMP is a branching point toward GMP and AMP formation. Enzymes such as IMP dehydrogenase and GMP synthetase are involved specifically in GMP formation, linking guanine production to overall purine metabolism.
Salvage pathways: Salvage enzymes recover free bases and nucleosides to conserve energy. In humans and other animals, guanine is salvaged by guanine phosphoribosyltransferase (encoded by the HPRT gene in humans), which converts guanine to GMP using phosphoribosyl pyrophosphate (PRPP). This pathway helps maintain nucleotide pools without de novo synthesis.
Nucleotide turnover and interconversion: Guanine nucleotides (GMP, GDP, GTP) are interconverted by kinases and phosphatases, supporting both genetic material synthesis and energy- and signaling-related roles. The balance among GMP, GDP, and GTP influences cellular energy management and regulatory networks.

Guanine in chemistry and health

Guanine-related chemistry underpins several areas of biology and medicine.

Oxidative damage: Guanine is susceptible to oxidation, producing 8-oxoguanine, a common lesion that can lead to G:C to T:A transversions if unrepaired. Base-excision repair pathways recognize and repair such oxidative damage, helping to preserve genome integrity.
Drugs and therapeutics: Guanine analogs appear in various therapeutic agents. For example, acyclovir is a guanine nucleoside analog used to treat viral infections by inhibiting viral DNA polymerases. Ribavirin is another nucleoside analog with activity against several RNA viruses. Purine analogs used in cancer therapy, such as 6-mercaptopurine, exploit purine metabolism to disrupt DNA synthesis in rapidly dividing cells. These compounds illustrate how guanine chemistry intersects with pharmacology and medicine.
Structural motifs and regulation: G-quadruplexes, which can form in guanine-rich regions, have implications for gene regulation, telomere maintenance, and genome stability. Understanding these structures informs research in genetics, aging, and cancer biology.

Guanine in research and technology

Beyond natural biology, guanine derivatives and its structural motifs enter diverse scientific areas.

Molecular biology techniques: Guanine-containing nucleotides are foundational to DNA sequencing, polymerase-based amplification, and various labeling approaches used in genomics and diagnostics.
Nanotechnology and biophysics: G-quadruplex structures provide model systems for studying nucleic acid mechanics and for designing nanoscale devices that respond to ionic conditions and molecular interactions.
Biotechnology and therapeutics: Guanine-containing nucleotides and their analogs are used in experimental therapies, enzymatic assays, and as probes for studying nucleotide metabolism and signaling networks.