Purine And Pyrimidine

Question 1

source of ribose

Answer 1

HMP shunt

Question 2

carbamoyl synthease role

Answer 2

there are 2
1. CS1-urea cycle(NH3+HCO3+atp)
liver mito
2.CS2-pyrimidine synthesis(CO2+glutamate+Atp)
cytoplasm ex rbc

Question 3

orotic aciduria cause

Answer 3

1. ornithine transcabamoylase def in urea cycle

2. enz defect in pyrimidine synthesis(from orotic acid to UMP)

Question 4

how is OTC defeciency diff. from orotic aciduria

Answer 4

in OTC def . there is decrease in urea/BUN and incrase in NH3 levels in blood

Question 5

5 FU targets

Answer 5

thymidylate synthatase(dUMP-dTMP)

Question 6

where is folic acid req in pyrimidine synthsis

Answer 6

during conversion of dUMP to dTMP which req methly group.(THF act as one C carrier)

Question 7

dihydrofolate reductase inhibited by which drugs

Answer 7

methotrexate eu
trimethoprim pro
pyrimithamine protozoal

Question 8

hydroxyurea inh which enz in pyr syn

Answer 8

ribonucleotide reductase(UDP-dUDP)

Question 9

diff bw pryimidine and purine pathway

Answer 9

pyrimidine: starts with synthsis of pyrimidine and then ribose
purine: starts with the ribose and then synthesis of purine

Question 10

what is inosine

Answer 10

nucleoside: hypoxanthine(base) + sugar

Question 11

allopurinol and 6mercaptopurine inhibit which enzyme in purine synthesis…used in cancer conditions

Answer 11

AMIDOTRANSFERASE

converts PRPP into 5phosphoribosylamine

Question 12

what is the level (enz)of regulation of purine synthesis

Answer 12

amidotransferase

inh by its products IMP ,GMP, AMP

Question 13

purine salvage pathway

Answer 13

amp-adenosine-(ADENOSINE DEAMINASE)-inosine-hypoxanthine
gmp-guanosine-guanine

hypoxanthine and guanine

1. xanthine and uric acid by xanthine oxidase
2. HGPRT to salvage pathway

Question 14

lesch nyhan

Answer 14

HGPRT defeciency
purines not salvaged
excess uric acid production
also decrease in feedback inhibition of amidotransferase(purine syn) which fuether increase uric acid production