Purine Metabolism

Question 1

What are the two subtypes of nucleotides?

Answer 1

Pyrimidines and purines

Question 2

How many rings do purines have in their nitrogenous base?

Answer 2

Two rings

Question 3

What is the major cellular source of energy?

Answer 3

ATP (adenosine triphosphate)

Question 4

What does cyclic AMP stand for?

Answer 4

Cyclic adenosine monophosphate

Question 5

True or False: Cyclic GMP serves as a second messenger.

Answer 5

True

Question 6

What are exogenous nucleotides?

Answer 6

Nucleotides obtained from the diet

Question 7

What are endogenous nucleotides?

Answer 7

Nucleotides synthesized by the body

Question 8

What is the first step in purine synthesis?

Answer 8

Creation of PRPP (5 phosphoribosyl 1 pyrophosphate)

Question 9

What does IMP stand for?

Answer 9

Inosine Monophosphate

Question 10

What are the basic components of nucleotides?

Answer 10

Phosphate group, ribose sugar, base

Question 11

What is the role of folate in purine synthesis?

Answer 11

Contributes single carbon groups

Question 12

List the amino acids that provide nitrogen for purine synthesis.

Answer 12

• Glutamine
• Aspartate
• Glycine

Question 13

What is the structure of purine bases?

Answer 13

Two rings with two nitrogen groups in each ring

Question 14

What is the rate limiting enzyme in purine synthesis?

Answer 14

Glutamine PRPP amidotransferase

Question 15

What distinguishes deoxyribonucleotides from ribonucleotides?

Answer 15

Deoxyribonucleotides lack a hydroxyl group

Question 16

How does ribavirin affect purine synthesis?

Answer 16

Inhibits IMP dehydrogenase, reducing GMP synthesis

Question 17

What is the function of mycophenolate?

Answer 17

Immunosuppressant that inhibits IMP dehydrogenase

Question 18

What are the potential fates of free floating purine bases?

Answer 18

• Converted to uric acid
• Remade into nucleotides (purine salvage)

Question 19

What enzyme is responsible for converting hypoxanthine or guanine to nucleotides?

Answer 19

HGPRT (hypoxanthine guanine phosphoribosyltransferase)

Question 20

What does APRT stand for?

Answer 20

Adenine phosphoribosyltransferase

Question 21

What chemotherapy drug mimics hypoxanthine and guanine?

Answer 21

6 mercaptopurine

Question 22

What is Azathioprine converted to in the body?

Answer 22

6 mercaptopurine

Question 23

What is the significance of PRPP in purine salvage?

Answer 23

Combines with free bases to regenerate nucleotides

Question 24

What is the structure of Azathioprine similar to?

Answer 24

6MP

Azathioprine has an extra molecule that is removed in the body, resulting in 6MP.

Question 25

What two purines are broken down into uric acid?

Answer 25

Hypoxanthine and guanine ## Footnote These purines are converted to xanthine and then to uric acid for excretion.

Question 26

What enzyme breaks down hypoxanthine into xanthine?

Answer 26

Xanthine oxidase

Question 27

What enzyme converts guanine into xanthine?

Answer 27

Guanase

Question 28

What is the role of adenosine deaminase?

Answer 28

Removes the amine group from adenosine and converts it into inosine

Question 29

What condition is associated with deficiency in adenosine deaminase?

Answer 29

Severe combined immunodeficiency syndrome

Question 30

What is gout?

Answer 30

A condition caused by excess uric acid in the plasma

Question 31

What are common symptoms of gout?

Answer 31

Pain, swelling, and redness in joints

Question 32

What is a classic location for gout symptoms?

Answer 32

Base of the big toe

Question 33

What can trigger a gout attack?

Answer 33

Under excretion or overproduction of uric acid

Question 34

What dietary factors can contribute to gout?

Answer 34

Consumption of purine-rich foods like meats and seafood

Question 35

What medication is used to treat gout?

Answer 35

Allopurinol

Question 36

What does allopurinol inhibit?

Answer 36

Xanthine oxidase

Question 37

What are the potential effects of co-administering allopurinol with azathioprine or 6MP?

Answer 37

Increased effects and toxicity of 6MP ## Footnote This occurs because allopurinol inhibits the metabolism of these drugs.

Question 38

What is Lesch Nyhan syndrome?

Answer 38

A rare disorder caused by absence of the HGPRT enzyme

Question 39

What results from the absence of the HGPRT enzyme?

Answer 39

Inability to salvage purines, leading to excess uric acid

Question 40

What are the neurological symptoms associated with Lesch Nyhan syndrome?

Answer 40

Hypotonia and choreo

Question 41

What behavior is commonly observed in children with Lesch Nyhan syndrome?

Answer 41

Self-mutilating behavior

Question 42

What is a classic presentation of Lesch Nyhan syndrome?

Answer 42

A male child with motor symptoms, self-mutilation, and gout

Question 43

Fill in the blank: Adenine is first converted back into the nucleotide _______.

Answer 43

Adenosine monophosphate

Question 44

What happens to inosine in the purine breakdown pathway?

Answer 44

It is converted into hypoxanthine

Question 45

What is the metabolic pathway that ramps up in Lesch Nyhan syndrome?

Answer 45

De novo purine synthesis pathway