synthesis of purines and pyrimidines

Question 1

what is the common precursor needed for purine ribonucleotides synthesis?

Answer 1

inosine monophosphate. It is produced by adding a purine base on a R5P

Question 2

purine ribonucleotide biosynthesis is regulated by?

Answer 2

feedback inhibition, feedforward activation

Question 3

what converts purines to its nucleotide form?

Answer 3

salvage reaction

Question 4

IMP is a precursor for?

Answer 4

AMP and GMP. NOTE that purines are initially formed as ribonucleotides and not free bases

Question 5

what is the first step of purine ribonucleotide biosynthesis?

Answer 5

activation of R5P, by ribose phosphate pyrophosphokinase, to form phosphoribosyl- pyrophosphate PRPP

Question 6

what is PRPP a precursor of?

Answer 6

of pyrimidine biosynthesis, and histadine and tryptophane synthesis

Question 7

step 2 of purine ribonucleotide formation? RATE CONTROLLING STEP

Answer 7

Is acquisition of N9, from glutamine (results in glutamate), by amidophosphoribosyl transferase, to produce phosphoribosylamine PRA

Question 8

kinases convert AMP and GMP into?

Answer 8

ATP and GTP

Question 9

the imidazole ring is formed by which enzyme

Answer 9

AIR synthetase

Question 10

In the urea cycle, citrulline is aminated to form

Answer 10

arginine

Question 11

THF is made up of what subunits

Answer 11

glutamates, pteroic acid

Question 12

what 2 drugs inhibit THF synthesis in bacteria

Answer 12

sulfonamides, p-aminobenzoic acid

Question 13

cyclization to form IMP is done by what enzyme

Answer 13

cyclohydrolase

Question 14

IMP dehydrogenase is inhibited by

Answer 14

immunosuppressant’s like mycophenolic acid, therefore the cell does not have enough guanosine for B and T cell proliferation

Question 15

How is adenine converted back to its nucleotide? AMP

Answer 15

by Adenine phosphoribosyltransferase APRT

Question 16

how is hypoxanthine and guanine converted back to their nucleotides? IMP/GMP

Answer 16

by hypoxanthine-guanine phosphoribosyl transferase

Question 17

what is pyrimidine synthesis?

Answer 17

UMP is synthesized as a pyrimidine base to which R5P is added

Question 18

CTP and UTP derive from?

Answer 18

UMP

Question 19

step 1 of pyrimidine synthesis is?

Answer 19

synthesis of carbamoyl phosphate by carbamoyl phosphate synthetase II, acting on glutamine+ATP+HCO3

Question 20

how is carbamoyl phosphate synthesized in the urea cycle

Answer 20

catalyzed by the mitochondrial enzyme carbamoyl phosphate synthetase I. AMMONIA is the nitrogen source

Question 21

ring closure in pyrimidine synthesis is done by?

Answer 21

dihydroorotase, resulting in dihydroorotate. This enzyme has FMN and nonheme, is on the outer surface of inner mitochondria membrane

Question 22

the last step of the formation of UMP is?

Answer 22

decarboxylation by OMP decarboxylase

Question 23

CTP from UTP is done by

Answer 23

CTP synthetase, using ATP and glutamine