Purine, Pyrimidine, Nucleotide Metabolism

Question 1

Purine vs Pyrimidine Synth

Answer 1

Purine: made on ribose, first makes IMP, I–> G &A as monophosphate
Pyrimidine: Base ring synth then attached to ribose, first makes UMP, U –> C as triphosphate

Question 2

Purine Initiator Step

Answer 2

o Ribose-5-P (from HMP shunt) + ATP to 5-Phosphoribosyl-1-pyrophosphate (PRPP) catalyzed by PRPP synthetase

Question 3

Purine Key Step

Answer 3

PRPP + glutamine to 5-Phosphoribosylamine (PRPP + N) by glutamine phosphoribosyl pyrophosphate amidotransferase

Question 4

Pyrimidine Key Step

Answer 4

2ATP + CO2 + Glutamine -> 2 ADP + Pi + Glutamate + Carbamoyl P by carbamoyl P synthetase II.
Activator: PRPP and ATP
Inhibitor: UTP

Question 5

SCID

Answer 5

lack adenosine deaminase = deoxyadenosine builds up = inhibits ribonucleotide reductase. Rapidly proliferating cells most affected (lymphocytes in children most affected)

Question 6

Lesch-Nylan

Answer 6

deficiency HGPRT in purine salvage = more de novo purine synth. Gout symptoms, self-mutilating behavior, mental disorders.