2. Pyrimidines are broken down via reduction The degradation of thymine produces mathylmalonyl-CoA, which can be converted to succinyl-CoA (a citric acid cycle intermediate) by the catalysis of of uracil and cytidine produces malonyl-CoA, which is one precursor for fatty acid biosynthesis To a limited extent, catabolism of pyrimidine nucleotides contributes to the energy metabolism of the cell
2. Pyrimidines are broken down via reduction • The degradation of thymine produces mathylmalonyl-CoA, which can be converted to succinyl-CoA (a citric acid cycle intermediate) by the catalysis of of uracil and cytidine produces malonyl-CoA, which is one precursor for fatty acid biosynthesis. • To a limited extent, catabolism of pyrimidine nucleotides contributes to the energy metabolism of the cell
C-CHs Degradation products of NADPH.H NADP pyrimidines can enter the citric acid cycle Ce CH. Dihydrothymine dahrydropyn ate/H, o I2N-C-NH-CH-CH-c B Ureidoisobutyrate CHs , O NHI+ HCO H N-CH -CH-C a-Ketoglutarate → Glutamate Propionyl-COA SuccinyI-CoA Methylmalonyl- semialdehyde
Propionyl-CoA Succinyl-CoA Degradation products of pyrimdines can enter the citric acid cycle
核苷酸的生物合成 1. Nucleotides are synthesized via either the de novo pathways or the salvage pathways In the de novo pathway simple precursors, including amino acids, PRPP, NH+ CO2r and one-carbon units(carried on Ha folate) are used In the salvage pathway the free bases and nucleosides released from nucleic acid breakdown are used
二、核苷酸的生物合成 1. Nucleotides are synthesized via either the de novo pathways or the salvage pathways • In the de novo pathway simple precursors, including amino acids, PRPP, NH4 +, CO2 , and one-carbon units (carried on H4 folate) are used. • In the salvage pathway the free bases and nucleosides released from nucleic acid breakdown are used
The free bases(a, G, C U, tare not intermediates during the de novo synthesis: the purine ring is assembled on ribose phosphate to make amp and gmp, the pyrimidine ring is first synthesized as orotate(乳清酸), Which is then attached to ribose phosphate before being converted to UTP and ctP(dTmp is made from dUMP) The deoxyribonucleotides(dNDPs)are synthesized by reduction of ribonucleotides (NDPS)
• The free bases (A, G, C, U, T) are not intermediates during the de novo synthesis: the purine ring is assembled on ribose phosphate to make AMP and GMP; the pyrimidine ring is first synthesized as orotate（乳清酸）, which is then attached to ribose phosphate before being converted to UTP and CTP (dTMP is made from dUMP). • The deoxyribonucleotides (dNDPs) are synthesized by reduction of ribonucleotides (NDPs)
2. Radioisotope tracer(放射同位素示踪 experiments revealed the origins of the atoms in the purine and pyrimidine rings Buchanan and Greenberg revealed this by feeding a variety of isotopically labeled compounds to pigeons(1940s) The atoms of the purine rings were found to be derived from formate, co2, Gly, Asp, and gIn The atoms of the pyrimidine rings were found to be derived from Asp, gIn and HCO3-
2. Radioisotope tracer(放射同位素示踪) experiments revealed the origins of the atoms in the purine and pyrimidine rings • Buchanan and Greenberg revealed this by feeding a variety of isotopically labeled compounds to pigeons (1940s). • The atoms of the purine rings were found to be derived from formate, CO2 , Gly, Asp, and Gln. • The atoms of the pyrimidine rings were found to be derived from Asp, Gln and HCO3 -