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Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar ( ribose or 2'-deoxyribose) whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and one or more phosphate groups.
Non-standard nucleosides are also found in both RNA and DNA and usually arise from modification of the standard nucleosides within the DNA molecule or the primary (initial) RNA transcript. Transfer RNA (tRNA) molecules contain a particularly large number of modified nucleosides.
In eukaryotes, modifications of RNA nucleotides are in general directed by small nucleolar RNAs (snoRNA; 60–300 nt), [32] found in the nucleolus and cajal bodies. snoRNAs associate with enzymes and guide them to a spot on an RNA by basepairing to that RNA. These enzymes then perform the nucleotide modification. rRNAs and tRNAs are extensively ...
Nucleic acid synthesis is catalyzed by either DNA polymerase or RNA polymerase for DNA and RNA synthesis respectively. [16] These enzymes covalently link the free -OH group on the 3’ carbon of a growing chain of nucleotides to the α-phosphate on the 5’ carbon of the next (d)NTP, releasing the β- and γ-phosphate groups as pyrophosphate ...
DNA and RNA also contain other (non-primary) bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytosine (m 5 C). In RNA, there are many modified bases, including those contained in the nucleosides pseudouridine (Ψ), dihydrouridine (D), inosine (I), and 7-methylguanosine ...
Nucleosides can be phosphorylated by specific kinases in the cell, producing nucleotides. Both DNA and RNA are polymers, consisting of long, linear molecules assembled by polymerase enzymes from repeating structural units, or monomers, of mononucleotides.
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Nucleic acid metabolism is a collective term that refers to the variety of chemical reactions by which nucleic acids (DNA and/or RNA) are either synthesized or degraded. Nucleic acids are polymers (so-called "biopolymers") made up of a variety of monomers called nucleotides.