Purine and Pyrimidine Formation

Question 1

What are the sources of pyrimidine?

Answer 1

HCO3, Gln, Asp, N-10 form of THF

Question 2

What are dietary pyrimidines converted into?

Answer 2

malonyl CoA, methyl malonyl CoA and succinyl CoA.

Question 3

What is the committed step in the synthesis of purines?

Answer 3

The formation of phosphoribosyl amine (PRA). It is the second step of the cycle.

Question 4

What enzyme converts PPRP to PRA (e.g. the committed step)?

Answer 4

glutamine:phosphororibosyl pyrophosphate.

Question 5

What inhibits and activates glutamine:phosphorylribosyl pyrophosphate?

Answer 5

PRPP activates, purines inhibit

Question 6

What amino acid is used in the committed step (PRPP to PRA)?

Answer 6

Glutamine. It is converted into glycine.

Question 7

What is ionisine monophosphate (IMP) converted into?

Answer 7

Adenylosuccinate monophosphate or xanthine mp

Question 8

What is de novo synthesis?

Answer 8

The synthesis of purines and pyrimidines from other compounds.

Question 9

After pyrimidines are asssembled, what are they attached to?

Answer 9

ribose

Question 10

What are purines attached to during synthesis?

Answer 10

ribose

Question 11

What is the first molecule in the purine de novo synthesis pathway?

Answer 11

alpha D ribose-5-phosphate.

Question 12

What enzyme converts alpha-D-ribose phosphate into PRPP?

Answer 12

PRPP synthetase

Question 13

What inhibits and activtes PRPP synthetase?

Answer 13

phosphate activates and purine nucleotides inhibit.

Question 14

What compound inhibits the PRA from forming IMP?

Answer 14

methotrexate

Question 15

What molecules are used in the nine step conversion of PRA to IMP?

Answer 15

CO2, Gln, Asp, Gly, and N10 THF

Question 16

What enzyme converts IMP into AMP?

Answer 16

Adenylosuccinate synthetase

Question 17

What is adenylosuccinate synthetase inhibited by?

Answer 17

AMP

Question 18

What enzyme converts adenylosuccinate monophosphate into adenosine monophosphate (AMP)?

Answer 18

adenylosuccinase

Question 19

What enzyme converts ADP/GDP into dADP/dGDP?

Answer 19

adenylosuccinase

Question 20

What is PRPP synthesized from?

Answer 20

Ribose and ATP.

Question 21

What enzyme converts IMP into XMP?

Answer 21

IMP dehydrogenase

Question 22

What does THF do in the nine stemp reaction of PRA to IMP?

Answer 22

Closes the purine ring that is synthesized.

Question 23

What is methotrexate used for?

Answer 23

Kidney cancer; it prevents cells from replicating DNA.

Question 24

The reaction of adenylosuccinate monophosphate to AMP results in the formation of what molecule that enters TCA?

Answer 24

fumarate

Question 25

What do AMP and GMP inhibit?

Answer 25

The enzymes (adenylosuccinate monophosphate synthetase and IMP dehydrogenase) that covert IMP into AMP & GMP.

Question 26

What is AMP/GMP synthesis stimulated by?

Answer 26

ATP and GTP

Question 27

UMP and UDP kinases allow for the conversion of UMP/UDP into what molecules?

Answer 27

UDP and UTP

Question 28

What is pyrimidine synthesized from?

Answer 28

carbamoyl phosphate and aspartate; aspartate carbamoylase facilitates the reaction.

Question 29

What is the first molecule in the pyrimidine synthesis pathway?

Answer 29

glutamine

Question 30

In pyrimidine synthesis, what is glutamine converted into?

Answer 30

carbamoyl phosphate

Question 31

In pyrimidine synthesis, what enzyme converts glutamine into carbamoyl phosphate?

Answer 31

carbamoyl phosphate synthetase II

Question 32

What amino acid is created upon the synthesis of glutamine to carbamoyl phosphate?

Answer 32

Glutamate; a molecule of ATP is also used.

Question 33

The conversion of carbamoyl phosphate to carbamoyl aspartate occurs when what enzyme is present?

Answer 33

aspartate transcarbamoylase

Question 34

What molecule is carbamoyl phosphate converted into?

Answer 34

carbamoyl aspartate

Question 35

Carbamoyl aspartate is converted into what molecule?

Answer 35

dihydro-orotate

Question 36

What enzyme converts carbamoyl aspartate into dihydro ortate?

Answer 36

dihydro orotase

Question 37

What is dihydro orotate converted into?

Answer 37

orotate

Question 38

Where do the first three steps of pyrimidine synthesis occur?

Answer 38

in the mitochondria

Question 39

What enzyme converts dihydro orotate into orotate?

Answer 39

dihydro orotate dehydrogenase

Question 40

What is orotate converted into?

Answer 40

OMP

Question 41

What enzyme converts orotate into OMP?

Answer 41

UMP synthase

Question 42

What enzyme converts OMP into UMP?

Answer 42

UMP synthase

Question 43

UMP is converted into what molecule?

Answer 43

UDP

Question 44

UDP can be converted into what two molecules?

Answer 44

UTP or dUTP

Question 45

UDP is converted into dUDP by what enzyme?

Answer 45

ribonucleotide reductase

Question 46

UTP is converted into CTP by what enzyme?

Answer 46

CTP synthase

Question 47

CTP is converted into dCTP by what enzyme?

Answer 47

ribonucleotide reductase

Question 48

dUMP is converted into dUTP by what enzyme?

Answer 48

thymidliate synthase

Question 49

Thymidiliate synthase is inhibited by what molecule?

Answer 49

5-fluorouracil

Question 50

What is the committed step of pyridine synthesis?

Answer 50

The conversion of carbamoyl phosphate into carbamoyl aspartate.

Question 51

What is orotic aciduria, and what enzyme in the pyrimidine synthesis pathway is it associated with?

Answer 51

The inability to synthesize pyrimidines, and hence DNA. It is associated with UMP synthase.

Question 52

What are deoxyribonucleotides formed from?

Answer 52

ribonucleotides

Question 53

What enzyme reduces ribonucleotides (and makes deoxyribonucleotides)?

Answer 53

ribonucleotide reductase

Question 54

What enzyme is inhibited by CTP and activated by AMP?

Answer 54

ATCase

Question 55

DNA is synthesized from what four molecules?

Answer 55

dATP, dGTP, dCTP and dTTP

Question 56

What is the salvage pathway?

Answer 56

A pathway that builds nucleotides from free bases.

Question 57

What enzyme in the purine salvage pathway converts an adenine base into AMP?

Answer 57

adenosine phosphoribyl transferase (APRT)

Question 58

What enzyme in the purine salvage pathway converts a guanine base into GMP?

Answer 58

HGPRT

Question 59

What are the sources of purine?

Answer 59

CO2, Gln, Gly, Asp, N-10 form of THF

Question 60

Which nucleotide is the limiting factor in DNA synthesis?

Answer 60

dTTP