Lecture 21: Nitrogen Metabolism

Question 1

With Hartnup’s disease, what amino acids are not properly reabsorbed?

Answer 1

Nonpolar amino acids

-mostly tryptophan

Question 2

With cystinuria, what amino acids are not properly reabsorbed?

Answer 2

Dibasic amino acids (COAL)

• Cystine
• Ornithine
• Arginine
• Lysine

Question 3

In Hartnup’s disease and cystinuria, where do you find decreased reabsorption?

Answer 3

Intestinal Lumen

Kidneys

Question 4

What is tryptophan a precursor to?

Answer 4

Serotonin
Melatonin
Niacin

Question 5

Describe symptoms of Hartnup’s disease.

Answer 5

Pellagra-like skin lesions

Neurologic manifestations

Question 6

Which vitamin deficiency can produce symptoms similar to Hartnup’s disease?

Answer 6

Niacin

Question 7

Describe symptoms of cystinuria.

Answer 7

Precipitation of cystine –> renal, ureteral, and bladder stones
Hematuria
Flank pain
Renal colic

Question 8

Describe phenylketonuria.

Answer 8

Lack of phenylalanine hydroxylase to convert phenylalanine to tyrosine
-Impairment of brain function

Question 9

Describe non-classical PKU.

Answer 9

Defects in cofactor for phenylalanine hydroxylase (PAH)

Question 10

Describe alkaproteinuria.

Answer 10

Black urine disease

-lack of homogentisic acid

Question 11

Describe ammonia toxicity.

Answer 11

Excessive ammonia due to disorders in urea cycle or liver failure –> highly toxic to brain and CNS

• disrupt pH balance
• depletion of glutamate

Question 12

Describe gout.

Answer 12

High levels of uric acid in blood

• due to diet rich in purines (meat, seafood, lentils) and alcohol
• Acidemia stimulates reabsorption

Question 13

Describe hyperammonemia.

Answer 13

Defects in any of the enzymes associated with urea cycle

Question 14

What is the role of carbamoyl phosphate synthetase II?

Answer 14

First step of de novo pyrimidine synthesis