Purines And Pyrimidines

Question 1

Purine Synthesis

Answer 1

Aspartate, CO2, Glycine, N10FTH (B9), glutamine

Built from a ribose base

PRPP adds to glutamine (via GPAT) to make 5’PRA… eventually IMP
IMP broken into AMP and GMP

Question 2

Vitamin B9

Answer 2

THF used for carbon transfer
Synthesis of nitorgenous bases

Formed from folic acid via DHFR

Methotrexate: prevents THF formation (cancer, arthritis)
- causes megaloblastic anemia long term

Question 3

Purine Degradation

Answer 3

Liver

AMP to IMP
IMP and GMP dephosphorylated
Hypoxanthine converted to Xanthine
Xanthine to uric acid

Question 4

ADA Deficiency

Answer 4

AR
Causes SCID: loss of immune function

low ADA: high dATP: inhibit RR: no deoxy nucleotides made: lymphocytes impacted

Question 5

Gout

Answer 5

Build up of uric acid, painful joints

Allopurinol inhibits xanthine oxidase to prevent uric acid formation
Cholchicine for acute cases, treats inflammation

Question 6

Purine Salvage

Answer 6

HGPRT converts hypoxanthine to AMP and GMP, back to IMP

Question 7

Lesch-Nyhan syndrome

Answer 7

Deficiency if HGPRT, build up purines and uric acid

Mental retardation, self mutilation

Question 8

Pyrimidine Synthesis

Answer 8

CPSII helps build ring from scratch
(+) PRPP
(-) UTP

Glutamine: CPSII: Orotate: PRPP: UMP to UTP, CTP

Question 9

UMP synthetase Deficiency

Answer 9

Orotic Aciduria

Orotate builds upm causes crystals in urine, megaloblastic anemia

(OTC deficiency in the Urea cycle builds up carbamoyl phosphate and leads to orotic aciduria as well)