Purine and Pyrimidine Metabolism Flashcards Preview

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Flashcards in Purine and Pyrimidine Metabolism Deck (37)
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1

What are nucleosides?

They are bases with the sugar group attached

2

What are nucleotides?

They are bases with the sugar group AND phosphate group(s)

3

What are the purines?

Adenine and guanine (2 rings)

4

What are the pyrimidines?

Cytosine, uracil and thymine (1 ring)

5

What is the order of purine biosynthesis?

The purine ring is built atom by atom onto the ribose group

6

What are the constituents that make up the purine ring?

-Aspartate
-Glycine
-Glutamine
-CO2
-N^10-Formyl-FH4

7

What is the first step of purine ring synthesis?

Ribose-5-Phosphate -> PRPP

R-5-Pi is activated

8

What is the second step of purine ring synthesis?

PRPP -> 5-phosphoribosylamine

9

Which is the regulated step of purine ring synthesis?

The second step:

PRPP -> 5-phosphoribosylamine

10

What is the enzyme catalyzing this reaction:

PRPP -> 5-phosphoribosylamine

Glutamine PRPP Amidotransferase

11

Where does ribose-5-phosphate in purine synthesis come from?

Pentose Phosphate Pathway

12

What nucleotide can branch into GMP or AMP?

IMP (inosinic acid)

13

How does allosteric inhibition of Glutamine PRPP Amidotransferase occur?

AMP and GMP are allosteric inhibitors of Glutamine PRPP Amidotransferase -> so it is negative feedback from the products

14

What is the function of 6-mercaptopurine?

It is an anti tumor agent that functions because it is converted into a nucleotide that will inhibit various steps of the purine synthesis, including Step 2, the rate limiting step

15

What are the constituents that make up the pyrimidine ring?

-Aspartate
-Glutamine
-CO2

16

What is the synthesis order of the pyrimidine ring?

Pyrimidine ring is synthesized FIRST separately from the ribose-5-phosphate and then it is attached to it

17

What is the regulated step of pyrimidine synthesis?

Glutamine + CO2 + ATP -> Carbamoyl Phosphate

18

What is the enzyme catalyzing the rate limiting step of pyrimidine synthesis?

Carbamoyl phosphate synthetase II

19

What is the pyrimidine precursor?

UMP

20

How does leflunomide treat arthritis?

Blocks pyrimidine synthesis by blocking dihydroorotate dehydrogenase

21

What enzyme converts dUMP to dTMP?

Thymidylate Synthase

22

What is the source of the methyl group for the conversion of dUMP to dTMP?

N^5/N^10-methylene THF

23

How does the anti tumor drug 5-fluorouracil work?

It is converted to f-dUMP which covalently binds to thymidylate synthase and inhibits the conversion of dUMP to dTMP.

24

What is the advantage of 5-fluorouracil in its side effects on normal cells?

As it only affects the conversion of dUMP, DNA synthesis is inhibited while RNA synthesis remains in tact.

25

How does the anti tumor agent methotrexate function?

It functions by inhibiting the function of dihydrofolate reductase which prevents the conversion of dihydrofolate to THF. This results in an accumulation of DHF which is toxic to the cell.

26

What is the function of ribonucleotide reductase?

It acts on the ribonucleotide-5'-diphosphate to form deoxyribonucleotide-5'-diphosphate

27

What is the cofactor necessary for the reaction catalyzed by ribonucleotide reductase?

Thioredoxin

28

Which hydroxyl group of ribose is converted to hydrogen?

2' group

29

What is a drug that acts as an inhibitor of ribonucleotide reductase?

Hydroxyurea

30

What is the function of HGPRTase?

There are 2 reactions:

Hypoxanthine + PRPP -> IMP + PPi
Guanine + PRPP -> GMP + PPi

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