Purine, Pyrimidine, and Nucleotide Metabolism - Parts 1 & 2

Question 1

___________ have two rings.

Answer 1

Purines (Two-rines)

Question 2

Compare and contrast the starting points for the synthesis of purines and pyrimidines.

Answer 2

Purines: starts with ribose

Pyrimidines: starts with base and adds sugar at the end

Question 3

The form of __________ in the mitochondria takes part in the urea cycle, while the cytosolic form participates in pyrimidine synthesis.

Answer 3

carbamoyl phosphate synthase

Question 4

In purine synthesis, ___________ is converted to AMP and GMP.

Answer 4

IMP

Question 5

__________ is converted to CTP.

Answer 5

UTP

Question 6

What is the first step in purine synthesis?

Answer 6

Ribose 5-phosphate
(PRPP synthetase) Regulated step
5-phosphoribosyl-1-pyrophosphate

Question 7

After PRPP synthetase, what is the next regulated step in the synthesis of IMP?

Answer 7

5-PRPP
(Glutamine phosphoribosyl pyrophosphate amidotransferase) Inhibited by GMP, AMP, and IMP; activated by PRPP
5-phosphoribosylamine

Question 8

These two enzymes are both allosterically inhibited by IMP, GMP, and AMP: _______________.

Answer 8

PRPP synthetase and glutamine PRPP amidotransferase

Question 9

The key regulated enzyme in pyrimidine synthesis is _________________.

Answer 9

2x ATP + CO2 + glutamate
(Carbamoyl phosphate synthetase II [in the cytosol])
Carbamoyl phosphate

Question 10

Ribonucleosides are converted to deoxyribonucleosides by the enzyme _________________.

Answer 10

ribonucleotide reductase

Question 11

ATP _____________ ribonucleotide reductase, while dATP _____________ it.

Answer 11

activates; deactivates

Question 12

Allopurinol inhibits ______________.

Answer 12

xanthine oxidase

Question 13

What enzyme converts adenosine to inosine?

Answer 13

Adenosine deaminase

Question 14

The two key enzymes in purine degradation are ________________.

Answer 14

(1) adenosine deaminase and (2) xanthine oxidase

Question 15

Those with Lesch-Nyhan cannot convert ________ to __________ or __________ to __________.

Answer 15

guanine; GMP

hypoxanthine; IMP

Question 16

Nucleoside is ______________, while nucleotide is _______________.

Answer 16

base and sugar; base, sugar, and phosphate

Question 17

In general, the body relies on ______________ when it needs nucleotides.

Answer 17

the salvage pathway

Question 18

True or false: methotrexate inhibits the production of pyrimidines.

Answer 18

False. Purines.

Question 19

What is created first in the pyrimidine synthesis pathway?

Answer 19

UMP; it must be converted to UTP before being converted to CTP

Question 20

The enzyme ribonucleotide reductase is inhibited by ____________.

Answer 20

dNTP

Question 21

Ribonucleotide reductase does not recognize _______.

Answer 21

TMP, so to get dTMP you need to make dUDP first

Question 22

Describe the overall process of purine breakdown.

Answer 22

First, the base is separated from the sugar, then the base is broken down to uric acid and excreted in the urine.

Question 23

After pyrimidines are separated from their sugars, what happens?

Answer 23

The ring is broken open.

Question 24

PRPP synthase is activated by high amounts of ______________.

Answer 24

inorganic phospate

Question 25

5-flurouracil inhibits the synthesis of _____________.

Answer 25

dTMP (because 5FU enters the enzyme thymidylate synthase and inhibits it)

Question 26

Without adenosine deaminase, dATP builds up in the blood. Why is this a problem?

Answer 26

Because dATP is a potent inhibitor of DNA synthesis

Question 27

Degradation of _____________ can lead to increased production of substrates for the TCA cycle.

Answer 27

pyrimidines