Many steps require an activated ribose sugar 0-POCH2O、H ATP AMP 0—POCH,O HH OH Ribose phos P-0-P-0 pyrophosphokinase HO OH HO OH O bose 5-phosphate 5-Phosphoribosyl-1-pyrophosphate (PRPP Activated carbon atom Ribose unit Space-filling model of 5-Phosphoribo syl-I-pyrophosphate(PRPP), the acti vated donor of the sugar unit in the biosynthesis of nucleotidesMany steps require an activated ribose sugar