Nitrogen Metabolism

Question 1

What is the first step of nitrogen removal? What enzyme?

Answer 1

Oxidative deamination via glutamate dehyrogenase

Question 2

What are three ways to get ammonia in the mitochondria?

Answer 2

Glutamate, Glutamine and Alanine

Question 3

What is the enzyme that converts ammonia to carbamoyl phosphate (the rate limiting step)

Answer 3

carbamoyl phosphate synthetase

Question 4

Who is the star of nitrogen flow?

Answer 4

glutamate (liver) and supporting is glutamine (other tissue)

Question 5

What is the general cause of hartnup disease and cystinuria?

Answer 5

inborn error of metabolism of amino acid resorption; deficiency in membrane transporters (intestinal and renal)

Question 6

Where in the kidneys does the reabsorption of AAs and glucose occur?

Answer 6

the proximal convoluted tubule

Question 7

What causes hartnup disease? How would you detect it?

Answer 7

defective transport of neutral/nonpolar amino acids (mostly tryptophan) for reabsorption; lab findings of elevated alanine, serine, threonine, valine, leucine, isoleucine, phenylalanine, tyrosine, tryptophan, glutamine, asparagine, and histidine in urine

Question 8

What causes Cystinuria? How would you detect it?

Answer 8

defective transport of dibasic amino acids (cystine, onithine, arginine, lysine) for reabsorption; cystine crystals in the kidneys identified by a positive nitroprusside test and patients present with abdominal pain (renal colic)

Question 9

What three things is tryptophan a precursor for?

Answer 9

serotonin, melatonin, and niacin (NAD)

Question 10

What is the treatment for hartnup disease?

Answer 10

niacin repletion and nicotinamide supplementation

Question 11

What is phenylketonuria caused by?

Answer 11

defective phenylalanine hydroxylase (PAH) which converts Phe to Tyr

Question 12

What is secondary PKU caused by?

Answer 12

tetrahydrobiopterin (TBH) deficiency (a cofactor of PAH)

Question 13

What is tyrosinemia?

Answer 13

elevated blood levels of tyrosine

Question 14

What is tyrosinemia type 1 and what is it caused by?

Answer 14

defect in fumarylacetoacetate hydrolase, which converts tryosine to fumarate; infants with this develop liver failure

Question 15

What is tyrosinemia type II caused by?

Answer 15

defective tyrosine aminotransferase which converts tyrosine to p-hydroxyphenylpyruvate

Question 16

What is tyrosinemia type III caused by?

Answer 16

defective p-hydroxyphenylpyruvate oxidase which converts p-hydroxyphenylpyruvate to homogentisate

Question 17

What is alkaptonuria? What is it caused by?

Answer 17

black urine disease; due to defective homogentisate oxidase

Question 18

What is ammonia toxicity?

Answer 18

excessive ammonia due to disorders in the urea cycle or liver failure can cause highly toxic effects on the brain and CNS

Question 19

What is gout caused by?

Answer 19

overproduction of uric acid (primary) or underexcretion of uric acid (secondary)

Question 20

What is hyperammonemia caused by?

Answer 20

defects in any of the six enzymes associated with the urea cycle (carbamoyl phosphate synthetase, ornithine transcarboxylase, arginosuccinate synthetase, arginosuccinate lyase, NAG synthase)

Question 21

What is the role of carbamoyl phosphate synthetase II in pyrimidine metabolism?

Answer 21

Carbamoyl phosphate synthetase II is involved in the first step of de novo pyrimidine synthesis and converts glutamine to carbamoyl phosphate

Question 22

What is the role of UDP glucuronyl transferase?

Answer 22

it conjugates bilirubin to become more soluble

Question 23

What is the difference between direct and indirect bilirubin?

Answer 23

direct bilirubin is conjugated while indirect is unconjugated

Question 24

Why does juandice occur in newborns?

Answer 24

during gestation, the placenta removes bilirubin and so after birth, the baby’s liver must take over. premature babies are more likely to have jaundice because of underdeveloped kidneys; pathologic jaundice due to SC anemia, hemolysis, etc.

Question 25

What error in heme catabolism can cause jaundice?

Answer 25

glucuronyl-bilirubin transferase