5phosphate

5-phosphate refers to a phosphate group esterified to the fifth carbon of a ribose or deoxyribose sugar, a common feature in nucleotides and various sugar phosphates. In biochemistry, the term often denotes a 5'-phosphate, the phosphate attached to the 5' carbon of the sugar in nucleotides and in the sugar-phosphate backbone of nucleic acids.

In nucleic acids, the backbone consists of alternating sugar and phosphate groups, with each nucleotide contributing a 5'-phosphate to link to the 3'-hydroxyl of the next sugar. Nucleoside monophosphates (AMP, CMP, GMP, UMP) contain a 5'-monophosphate. The presence and position of the 5'-phosphate influence RNA and DNA synthesis, processing, and stability. In eukaryotes, mature mRNA typically features a 5' cap structure derived from an initial 5'-triphosphate end, which is subsequently modified to a 5' cap rather than a simple 5'-phosphate.

In metabolism, ribose-5-phosphate is a key intermediate produced by the pentose phosphate pathway and serves as a precursor for nucleotide biosynthesis. Phosphoribosyl pyrophosphate (PRPP) is formed from ribose-5-phosphate and acts as an activated donor of ribose-5-phosphate in the de novo synthesis of purine and pyrimidine nucleotides. Deoxyribose-5-phosphate, generated from ribose-5-phosphate, is involved in the production of deoxyribonucleotides.

Enzymatically, kinases add 5'-phosphate groups to substrates, while phosphatases remove them. The 5'-phosphate is therefore a key functional handle in nucleotide metabolism, nucleic acid biology, and related signaling and repair processes.