Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine. In DNA, guanine is paired with cytosine. The guanine nucleoside is called guanosine.
Nucleotides are organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecules within all life-forms on Earth. Nucleotides are obtained in the diet and are also synthesized from common nutrients by the liver.
Guanosine-5'-triphosphate (GTP) is a purine nucleoside triphosphate. It is one of the building blocks needed for the synthesis of RNA during the transcription process. Its structure is similar to that of the guanosine nucleoside, the only difference being that nucleotides like GTP have phosphates on their ribose sugar. GTP has the guanine nucleobase attached to the 1' carbon of the ribose and it has the triphosphate moiety attached to ribose's 5' carbon.
Guanosine diphosphate, abbreviated GDP, is a nucleoside diphosphate. It is an ester of pyrophosphoric acid with the nucleoside guanosine. GDP consists of a pyrophosphate group, a pentose sugar ribose, and the nucleobase guanine.
In biochemistry, a ribonucleotide is a nucleotide containing ribose as its pentose component. It is considered a molecular precursor of nucleic acids. Nucleotides are the basic building blocks of DNA and RNA. Ribonucleotides themselves are basic monomeric building blocks for RNA. Deoxyribonucleotides, formed by reducing ribonucleotides with the enzyme ribonucleotide reductase (RNR), are essential building blocks for DNA. There are several differences between DNA deoxyribonucleotides and RNA ribonucleotides. Successive nucleotides are linked together via phosphodiester bonds.
Guanosine monophosphate (GMP), also known as 5′-guanidylic acid or guanylic acid, is a nucleotide that is used as a monomer in RNA. It is an ester of phosphoric acid with the nucleoside guanosine. GMP consists of the phosphate group, the pentose sugar ribose, and the nucleobase guanine; hence it is a ribonucleoside monophosphate. Guanosine monophosphate is commercially produced by microbial fermentation.
Purine nucleoside phosphorylase, PNP, PNPase or inosine phosphorylase is an enzyme that in humans is encoded by the NP gene. It catalyzes the chemical reaction
Nucleic acid metabolism is a collective term that refers to the variety of chemical reactions by which nucleic acids are either synthesized or degraded. Nucleic acids are polymers made up of a variety of monomers called nucleotides. Nucleotide synthesis is an anabolic mechanism generally involving the chemical reaction of phosphate, pentose sugar, and a nitrogenous base. Degradation of nucleic acids is a catabolic reaction and the resulting parts of the nucleotides or nucleobases can be salvaged to recreate new nucleotides. Both synthesis and degradation reactions require multiple enzymes to facilitate the event. Defects or deficiencies in these enzymes can lead to a variety of diseases.
Purine metabolism refers to the metabolic pathways to synthesize and break down purines that are present in many organisms.
Guanosine monophosphate synthetase, also known as GMPS is an enzyme that converts xanthosine monophosphate to guanosine monophosphate.
Ribose-phosphate diphosphokinase is an enzyme that converts ribose 5-phosphate into phosphoribosyl pyrophosphate (PRPP). It is classified under EC 2.7.6.1.
In enzymology, a phosphopentomutase is an enzyme that catalyzes the chemical reaction
In enzymology, a nucleoside-diphosphatase (EC 3.6.1.6) is an enzyme that catalyzes the chemical reaction
In enzymology, an alpha,alpha-trehalose-phosphate synthase (GDP-forming) is an enzyme that catalyzes the chemical reaction
In enzymology, an uridine phosphorylase is an enzyme that catalyzes the chemical reaction
In enzymology, a xanthine phosphoribosyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a mannose-1-phosphate guanylyltransferase is an enzyme that catalyzes the chemical reaction
In enzymology, a mannose-1-phosphate guanylyltransferase (GDP) is an enzyme that catalyzes the chemical reaction
In enzymology, a nucleoside-triphosphate-aldose-1-phosphate nucleotidyltransferase is an enzyme that catalyzes the chemical reaction
Xanthosine phosphorylase, also known as inosine-guanosine phosphorylase, is a catalytic enzyme encoded by the XapA gene in E. coli. The presence of xanthosine is known to induce the synthesis of xanthosine phosphorylase by the XapA gene. The enzyme's main functions are nucleoside phosphorolysis and the synthesis of nucleotides, making it a member of the purine nucleoside phosphorylase group. This protein can degrade all purine nucleosides except adenosine, deoxyadenosine, hypoxanthine arabinoside. These degradation reactions are reversible in vitro, however, phosphorolysis dominates in vivo. Xanthosine phosphorylase is localized in the cytoplasm because these degradation functions take place there. Xanthosine phosphorylase preferentially uses the neutral form of xanthosine over its monoanionic form because it prefers to be in a neutral environment.
