 nucleotides are the activated precursors of nucleic acids. As such, they are necessary for the replication of the genome  an adenine nucleotide, ATP, is the universal currency of energy. A guanine nucleotide, GTP, also serves as an energy source for a more select group of biological processes.  Third, nucleotide derivatives such as UDP-glucose participate in biosynthetic processes such as the formation of glycogen.  nucleotides are essential components of signal-transduction pathways. cyclic AMP and cyclic GMP are second messengers that transmit signals both within and between cells.

AdenineGuanine Thymine/UracilCytosine Two Purines Two Pyrimidines

 For both purines and pyrimidines there are two means of synthesis (often regulate one another)  de novo (from bits and parts)  salvage (recycle from pre-existing nucleotides) Salvage Pathwayde novo Pathway

5’

 Committed step: This is the point of no return  Occurs early in the biosynthetic pathway  Often regulated by final product (feedback inhibition) X

 Pyrimidine rings are synthesized independent of the ribose and transferred to the PRPP (ribose)  Generated as UMP (uridine 5’-monophosphate) Synthesized from: –Glutamine –CO 2 –Aspartic acid –Requires ATP UracilCytosine

 Atoms derived from:  Aspartic acid  Glycine  Glutamine  CO 2  Tetrahydrofolate  Also requires  4 ATP’s Purines are synthesized on the Ribose ring Committed Step Inhibited by AMP, GMP, IMP X

Hypoxanthine or Guanine +PRPP= IMP or GMP + PPi Hypoxanthineguanosylphosphoribosyl transferase (HGPRTase) Adenine+PRPP= AMP + PPi Adeninephosphoribosyl transferase (APRTase)

 Synthesized on PRPP  Regulated by GTP/ATP  Generates IMP  Requires Energy  Synthesized then added to PRPP  Regulated by UTP  Generates UMP/CMP  Requires Energy Both are very complicated multi-step process which your kindly professor does not expect you to know in detail