Purine Nucleotides

Question 1

how are most purine bases obtained?

Answer 1

via de novo synthesis. can also be taken from salvage pathways

Question 2

how does folic acid affect purine synthesis?

Answer 2

2 steps require N-formyl-THF-transferases, so folic acid deficiency inhibits de novo synthesis

Question 3

what are the building blocks needed for de novo purine biosynthesis?

Answer 3

glutamine, glycine, 10-formyl-THF, CO2, and aspartate

Question 4

PRPP synthetase

Answer 4

highly regulated step in the process of both purine and pyrimidine synthesis.

inhibited by: IMP, AMP, GMP
activated by: Pi

Question 5

PRPP amidotransferase

Answer 5

first step in purine biosynthesis, also highly regulated

activated by: PRPP levels
inhibited by: IMP, AMP, GMP

Question 6

what is the end product of purine biosynthesis

Answer 6

IMP, which is then converted to either AMP (adenylosuccinate synthetase) or GMP (IMP dehydrogenase)

Question 7

how is AMP/GMP synthesis regulated

Answer 7

negative feedback loop back on their respective enzymes from IMP (adenylosuccinate synthetase and IMP dehydrogenase)

Question 8

describe purine salvage pathways

Answer 8

free purine bases that are the result of normal cellular turnover are converted to nucleoside triphosphates by HGPRT and APRT

HGPRT converts hypoxanthine and guanine to IMP and GMP respectively

APRT converts adenine to AMP

Question 9

Lesch-Nyhan syndrome

Answer 9

deficiency in HGPRT leads to neurological deficits and overproductive gout

Question 10

describe purine degradation

Answer 10

degraded to uric acid mediated by xanthine oxidase. elevated levels of uric acid lead to gout, which is the precipitation of uric acid