7. Nitrogen Metabolism

Question 1

What is the main nitrogen shuffling molecule for the liver?

Answer 1

Glutamate

Question 2

What is the main nitrogen shuffling molecule for the rest of the body (other than the liver)?

Answer 2

Glutamine

Question 3

What enzyme catalyzes the rate limiting step of the urea cycle?

Answer 3

Carbamoyl phosphate synthetase 1

Question 4

What sort of amino acids have a defective reabsorption in Hartnup disease?

Answer 4

Nonpolar amino acids

Question 5

What sort of amino acids fail to reabsorb in cystinuria?

Answer 5

Dibasic amino acids

Question 6

Tryptophan is a precursor for what 3 important molecules?

Answer 6

Serotonin, Melatonin, and Niacin

Question 7

Four of the diseases we studied in this lecture are associated with the phenylalanine to fumarate pathway. What are those diseases, and in what order do they appear in the pathway?

Answer 7

Phenylketonuria

Tyrosinemia II & Albinism

Tyrosinemia III

Alkaptonuria

Tyrosinemia I

Question 8

What is the cause of secondary phenylketonuria?

Answer 8

Defects in the biosynthesis or regeneration of tetrahydrobiopterin

Question 9

What enzyme is defective in alkaptonuria?

Answer 9

Homogentisate oxidase

Question 10

What are the two effects of ammonia toxicity discussed in class?

Answer 10

Ammonia buildup pushes the glutamate to alpha ketoglutarate reaction away from alpha ketoglutarate, which prevents it from going into the TCA cycle.

Also, excess ammonia favors glutamine formation from glutamate, which reduces the amount of glutamate overall, decreasing the amount available to make GABA.

Question 11

The majority of urea cycle enzyme diseases have what sort of heredity?

Answer 11

Autosomal recessive

(The noted exception is ornithine transcarbamoylase)

Question 12

What is the function, location, and activator for CPSase II?

Answer 12

Pyrimidine synthesis

Cytosolic

PRPP

Question 13

What is the function, location, and activator for CPSase I?

Answer 13

Urea cycle

Mitochondrial

NAG

Question 14

What is the function of UDP glucuronyl transferase?

Answer 14

It conjugates bilirubin

Question 15

In a newborn, what sort of condition (generally speaking) could cause physiological jaundice to transfer to pathological jaundice?

Answer 15

Anything that causes heme turnover. Blood loss, bruising, anemia, (including sickle-cell), or even infection, because antibiotics decrease/diminish UDP glucuronyl transferase