Pyrimidine Metabolism

Step 1 of Pyrimidine Synthesis / Role of CPS2

HCO₃^- + Glutamine + Water + 2 ATP → Carbamoyl Phosphate + Glutamate + 2 ADP + P_i

Activators of CPS2

PRPP and IMP

Inhibitors of CPS2

UMP, UDP, UTP, and CTP

Rate Limiting Step/Enzyme of Pyrimidine Synthesis

CPS2

Step 2 of Pyrimidine Synthesis / Role of Aspartate Transcarbamoylase (ATCase)

Carbamoyl Phosphate + Aspartate → Carbamoyl Aspartate + P_i

Activators of ATCase

ATP and GTP

Inhibitors of ATCase

UTP and CTP

Step 3 of Pyrimidine Synthesis

A lot of things but know that PRPP gets added to Orotate → OMP

Step 4 of Pyrimidine Synthesis / Role of UMP Synthase

OMP + Water → UMP + HCO₃^-

Note: In prokaryotes, the enzyme is different, OMP Decarboxylase

Step 5 of Pyrimidine Synthesis

a) UMP + ATP → UDP + ADP

b) UMP + 2 ATP → UTP + 2 ADP

Step if UTP was formed / Role of CTP Synthetase

UTP + Water + ATP + Glutamine → CTP + ADP + P_i + Glutamate

Activators of CTP Synthetase

GTP

Inhibitors of CTP Synthetase

CTP

Activators of CTP Synthetase

GTP

Inhibitor of RNR

dATP

Circumstances when CDP or UDP are turned into dCDP and dUDP

ATP binds to activity site and ATP or dATP bind to specificity site

Circumstance when GDP is turned into dGDP

ATP binds to activity site and dTTP binds to specificity site

Circumstance when ADP is turned into dADP

ATP binds to activity site and dGDP binds to specificity site

Function of dUMP

To get turned into dTMP

Role of Thymidylate Synthase

Formation of dTMP

dUMP + N-5,10-Methylenetetrahydrofolate → dTMP + 7,8-DHF

Turning Cytosine to Uracil

Cytosine → Uracil + NH₃ using Cytosine Deaminase

End products of Uracil Degradation

Acetyl CoA, NADP⁺, NH₃, and HCO₃^-

End Products of Thymine Degradation

Succinyl CoA, NADP⁺, NH₃, and HCO₃^-

Role of RNR

Turn ribose containing bases to deoxyribose containing bases (Ribose → Deoxyribose)

C2 on Pyrimidine Ring

From HCO₃^-

N3 on Pyrimidine Ring

From Glutamine

N1, C4, C5, C6 on Pyrimidine Ring

From Aspartate