Editing Ribonucleotide (section)

===Linking successive nucleotides===

Ribonucleotides are linked together to form RNA strands via [[phosphodiester bonds]]. The 5'-phosphate group of one nucleotide is linked to the 3'-hydroxyl group of the next nucleotide, creating a backbone of alternating phosphate and pentose residues. There is no phosphodiester bond at each end of the polynucleotide.<ref>{{cite book |last=Raymond |first=Kenneth W. |title=General, organic, and biological chemistry: an integrated approach |year=2010 |publisher=Wiley |isbn=978-0-470-55124-0 |edition=3rd |oclc=699600111}}</ref> Phosphodiester bonds are formed between ribonucleotides by the enzyme [[RNA polymerase]]. The RNA chain is synthesized from the 5' end to the 3' end as the 3'-hydroxyl group of the last ribonucleotide in the chain acts as a nucleophile and launches a hydrophilic attack on the 5'-triphosphate of the incoming ribonucleotide, releasing pyrophosphate as a by-<ref>{{cite book |editor1-first=Moselio |editor1-last=Schaechter |editor2-first=Joshua |editor2-last=Lederberg |title=The Desk Encyclopedia of Microbiology |year=2004 |publisher=Elsevier |location=Amsterdam |isbn=0-12-621361-5 |edition=1st |oclc=1055874153}}</ref> product. Due to the physical properties of the nucleotides, the backbone of RNA is very hydrophilic and polar. At neutral pH, nucleic acids are highly charged as each phosphate group carries a negative charge.<ref>{{cite book |last1=Turner |first1=Phil |last2=McLennan |first2=Alexander |last3=Bates |first3=Andy |last4=White |first4=Mike |display-authors=1 |title=Molecular Biology |series=Instant Notes |year=2005 |publisher=CRC, Taylor & Francis |isbn=0-415-35167-7 |edition=3rd |oclc=61745541}}</ref>

Both DNA and RNA are built from nucleoside phosphates, also known as mononucleotide monomers, which are thermodynamically less likely to combine than amino acids. Phosphodiester bonds, when hydrolyzed, release a considerable amount of free energy. Therefore, nucleic acids tend to spontaneously hydrolyze into mononucleotides. The precursors for RNA are GTP, CTP, UTP and ATP, which is a major source of energy in group-transfer reactions.<ref>{{cite book|last=Nelson|first=David|title=Lehninger Principles of Biochemistry|year=2008|publisher=W H Freeman and Co|pages=274–275}}</ref>