Purine Metabolism

Question 1

What is the difference between a nucleoside and nucleotide?

Answer 1

Nucleoside is a sugar and base with no phosphates - nucleotide has phosphates.

Question 2

Is folate required for inosinate production?

Answer 2

Yup, in two steps.

Question 3

What is the energy source for AMP production? What is the energy source for GMP production?

Answer 3

AMP requires GTP, GMP requires ATP

Question 4

Name three possible causes of Gout.

Answer 4

1. Defective HGPRT (converts PRPP to GMP or IMP)
2. Defective feedback inhibition on PRPP synthetase
3. GRPase deficiency

In all cases, PRPP builds up with activates the de novo purine synthesis pathway. All these purines must be metabolized, leading to increased uric acid levels.

Question 5

How is Gout treated?

Answer 5

Allopurinol competes for the active site of xanthine oxidase to lower uric acid production.

Question 6

What is the defect in Lesch-Nyhan Syndrome? What are the symptoms?

Answer 6

HGPRT. Self-mutilation, mental illness, Gout-like symptoms due to elevated uric acid.

Question 7

What is the major symptom of adenosine deaminase deficiency (SCID)?

Answer 7

No immune system

Question 8

How do sulfonamides inhibit bacterial growth?

Answer 8

They stop folic acid synthesis.

Question 9

How does 6-Mercaptopurine treat leukemia?

Answer 9

Is is an analogue of hypoxanthine, which prevents production of AMP and GMP, leading to inhibited nucleotide synthesis in cancer cells.