Metabolism of Pyrimidine nucleotides

Question 1

1.CO2 -> Carbamoyl Phosphate

Answer 1

Gln -> Glu
ATP -> ADP
enzyme: CARBAMOYL P SYNTHETASE
uses CAD Py1-3

Question 2

2.Carbomoyl P -> Carbamoyl Asp

Answer 2

+Asp
enzyme: ASP TRANSCARBAMOYLASE
uses CAD Py1-3

Question 3

3.Carbamoyl Asp -> Dihydro-orotate

Answer 3

-H20
enzyme: DIHYDRO OROTASE
uses CAD Py1-3

Question 4

4.Dihydro orotate -> Orotate

Answer 4

NAD+ -> NADH
enzyme: H2OA DEH
uses mito Py4

Question 5

5. Orotate -> Orotidylate OMP

Answer 5

PRPP -> PPi
enzyme: OA PRT
uses UMP-S Py5

Question 6

6. Orotidylate -> UMP

Answer 6

-CO2
enzyme: OMP DECARBOXYLASE
uses UMP-S Py6

Question 7

7. UMP -> UDP

Answer 7

ATP -> ADP

enzyme: PYRIMIDINE MONOPHOSPHATE KINASE

Question 8

8. UDP -> UTP

Answer 8

ATP -> ADP

enzyme: PYRIMIDINE DIPHOSPHATE KINASE

Question 9

9.UTP -> CTP

Answer 9

Gln -> Glu
ATP -> ADP +Pi
enzyme: CTP SYNTHETASE

Question 10

Regulation of de novo synthesis

Answer 10

CAD complex:single polypeptide, 3 active centers

inhibit: UTP
activate: PRPP

UMP-S
inhibit: UMP

Question 11

Orotic aciduria

Answer 11

1. UMP-S deficiency
2. Inhibition of UMP-S
3. Ornithine transcarbamoylase deficiency
   - hyperammonemia, carbamoylP accumulation
   - OA overproduction

Question 12

Catabolism of UMP/TMP

Answer 12

UMP - 5 NUCLEOTIDASE - uridine (CYTIDINE DEAMINASE) - CO2,NH3, B alanine

Question 13

Catabolism of CPM

Answer 13

CMP - 5 NUCLEOTIDASE - cytidine - CO2,NH3,B alanine

Question 14

Salvage reactions

Answer 14

uridine - URIDINE KINASE - UMP

cytidine - CYTIDINE KINASE - CMP - CYTIDYLATE DEAMINASE - UMP

Question 15

Difference in CPS1 and CPS2

Answer 15

CPS1:

• mitochondria
• urea cycle
• ammonia
• activator: N-acetyl-glutamate

CPS2:

• cytosol
• pyrimidine synthesis
• gamma amide group of glutamine
• activator: PRPP, inhibitor: UTP