Urea cycle

Question 1

RLE of urea cycle

Answer 1

CPS-1

Question 2

Required by CPS-1

Answer 2

ATP (adds phosphate to make carbamoyl PHOSPHATE)

N-acetylglutatmate (cofactor)

Question 3

Nitrogen source for UREA

Answer 3

NH3 provides one amino group
Aspartate provides the other amino group

C=O provided by CO2

Question 4

Enzyme that converts ornithine and carbamoyl phosphate into citrulline

Answer 4

ornithine transcarbamoylase

Question 5

Why does orotic acid increase in ornithine transcarbamylase deficiency?

Answer 5

OTC catalyzes reaction between carbamoyl phosphate and ornithine to make citrulline.

OTC deficiency results in ACCUMULATION of carbamoyl phosphate

carbamoyl phosphate is metabolized to OROTIC ACID

Question 6

Lab findings of OTC deficiency

Answer 6

Orotic acid increased in blood and urine
BUN decreased (urea cycle is defective)
Hyperammonemia

Question 7

Symptoms of hyperammonemia

Answer 7

Hepatoencephalopathy:
slurring of speech
somnolence
vomiting
cerebral edema
blurring of vision

Question 8

Hyperammonemia causes:

Answer 8

hepatocyte damage
urea cycle enzyme deficiencies (N-acetylglutamate synthase,
UMP synthase deficiency (pyrimidine synthesis)

Question 9

Treat hyperammonemia:

Answer 9

low protein diet

If urea cycle defect:
phenylbutryate (binds certain amino acids)
benzoate
biotin (stimulate ornithine transcarbamylase)