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A nucleoside is a nucleobase with a five-carbon sugar (either ribose or deoxyribose). It is a glycoside formed from the hydrolysis of nucleic acid. A purine nucleoside is one in which the nucleobase is a purine, such as guanine in guanosine. Guanosine is a nucleoside consisting of guanine and ribose sugar linked by β-N9-glycosidic bond. When a phosphate group is covalently attached to the sugar, it forms a nucleotide. An example of a nucleotide wherein three phosphate groups are attached to guanosine is guanosine triphosphate (GTP), one of the building blocks of RNA synthesis.
Guanosine is found in all living organisms as a structural component of RNA. The chemical formula is C10H13N5O5. Its molar mass is 283.241 g/mol. It dissolves readily in acetic acid and slightly soluble in water. It is not soluble though in ethanol, benzene, and chloroform.
Guanosine vs. Deoxyguanosine
Nucleosides may be classified into ribonucleosides or deoxyribonucleosides, depending on the sugar component. Guanosine is a ribonucleoside due to its ribose sugar. In contrast, deoxyguanosine is a deoxyribonucleoside for having a sugar component that is deoxyribose. Deoxyguanosine differs from guanosine by having a hydroxyl group replaced by hydrogen at the 2′ position of the sugar moiety. In deoxyguanosine, the N9 nitrogen of guanine is attached to the C-1 of deoxirobose ring. Deoxyguanosine pairs up with deoxycytidine in DNA whereas guanosine pairs with cytidine in RNA.
Common biological reactions
Common biological reactions
Nucleosides such as guanosine can be produced by de novo synthesis pathways in the liver. Nevertheless, they may also be obtained from the diet. When the diet contains nucleotides, the body digests them by nucleotidases to produce nucleosides and phosphates. Nucleosides are degraded into their subcomponents (i.e. nucleobases and sugar) by the action of nucleosidases in the lumen of the digestive tract.
Guanosine, just as the other nucleosides, can give rise to nucleotides. When phosphorylated by kinases, the nucleoside is converted into a nucleotide. Thus, a nucleotide is a nucleoside with a phosphate group. Guanosine can form guanosine monophosphate (GMP, i.e. guanosine with a single phosphate group), cyclic guanosine monophosphate (cGMP), guanosine diphosphate (GDP, i.e. guanosine with two phosphate groups), and guanosine triphosphate (GTP, i.e. guanosine with three phosphate groups). GTP, in particular, is one of the building blocks for the formation of RNA. Structurally, guanine is attached to the C-1 of the ribose while the phosphate moiety is attached to the C-5 of the ribose. Apart from nucleic acid synthesis, they are also involved in other biochemical processes, e.g. protein synthesis, photosynthesis, muscle contraction, and intracellular signal transduction (cGMP).
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