Question

1. how do cells salvage purines?

2.  The pool of dNTPs varies in size over the course of the cell cycle, and peaks at the beginning of S-phase (synthesis), while the NTP pool is relatively stable, and much larger. Given what you know about the roles of these nucleotides, why does this make sense?

Answer 1

1. Cells salvage purines with the help of salvage pathway. Here, in this process nucleotides are synthesised from intermediates in the degradative pathway. It is essentially used to recover bases and nucleotides during degradation of RNA and DNA.

For purines, activated ribose 5 phosphate is added to the bases by phosphoribosyltransferases creating nucleoside monophosphate. The phosphoribosyltransferases are of two kinds namely  adenine phosphoribosyltransferase (APRT) and hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Adenine phosphoribosyltransferase (APRT) is used for the synthesis of AMP i.e Adenosine mono phosphate from Adenine while hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is used for the synthesis of Guanosine mono phosphate from Guanine.