20. Nitrogen Metabolism

Question 1

Reabsorption of what is defective in Hartnup disease?

Answer 1

Defective transport of neutral AA, particularly tryptophan

Question 2

Reabsorption of what is defective in cystinuria?

Answer 2

Defective transport of dibasic amino acids, particularly cystine

COAL

Question 3

What causes PKU? What are the main symptoms of it?

Answer 3

Defects in phenylalanine hydroxylase activity (used to process Phe). Leads to musty odor in urine. Also leads to impaired brain function due to byproducts. Patient cannot eat Phe, tyrosine cannot be made.

Question 4

What causes alkaptonuria? What are the main symptoms of it?

Answer 4

Defective homogentisate oxidase, used in Tyr degradation. Black urine, dark sclera.

Question 5

How does ammonia toxicity effect brain performance?

Answer 5

It is neurotoxic because it shifts glutamine to be made instead of glutamate, so there are less neurotransmitters in the brain.

Question 6

What causes gout? What can it be treated with?

Answer 6

High levels of uric acid due to underexcretion that deposit in extremity joints due to their lower temperature. High risk for heavy drinkers.

Treated with allopurinol.

Question 7

What is hyperammonemia?

Answer 7

Occurs with defects in any of the enzymes/transporters in the urea cycle.`

Question 8

Defect in carbamoyl phosphate synthetase II leads to what pathway being defective?

Answer 8

PPPP