Nitrogen Metabolism

Question 1

what do aa get broken down into?

Answer 1

NH3 (toxic, tx to liver, converted to urea, excreted) + alpha-ketoacid

Question 2

Essential AA

Answer 2

PVT TIM HALL

phenylalanine
valine
threonine

tryptophan
isoleucine
methionine

histidine
arginine
leucine
lysine

Question 3

positive N balance

Answer 3

Net synthesis of protein

Growth (body builder, children)
Pregnancy
Convalescence (recovering from injury)

Question 4

Negative N balance

Answer 4

Net breakdown protein

protein deficiency
essentail aa deficiency
low carb diet
low cal diet/undernutrition
wasting disease (Cancer/ infection)

Question 5

How is Ammonia Made?

Answer 5

aa+alpha-ketoglutarate –>[transamination (b6)] –> alpha ketoacid + glutamate

glutamate –> [glutamate DH//oxidative deamination] –> ammonia

Question 6

Detoxification of Ammonia

Answer 6

Liver Cells, mitochondria

NH4+ + HCO3- –> [carbamyl phosphate synthestase//N-acetylglutamate allosteric activator] –> carbomyl phosphate (enters urea cycle)

Question 7

What enters urea cycle?// sources of N

Answer 7

Carbamoyl phsphate & ASPARTATE

Question 8

Urea cycle

Answer 8

makes urea and arginine ultimately. Liver

ORNITHINE [Carbamoyl Phosphate]–> [ornithine transcarbamoylase]

–> CITRULLINE [aspartate] –> [arginosuccinate synthetase]

–> ARGINOSUCCINATE –> [argininosuccinate lyase]

–> ARGININE –> urea & [arginase]

–> ORNITHINE

Question 9

Urea Cycle Enzyme deficiency

Answer 9

Hyperammonemia with CNS toxicity:
ANY disruption of urea cycle causes INCREASE in ammonia.

substrate of missing enzyme accumulates
x carbamyl phosphate synthetase (NH4)
x ornithine transcarbamoylase (Ornithine)
x argininosuccinate synthetase (citrulline)
x argininosuccinate lyase (arginosuccinate)
x arginase (arginine)

Question 10

Hyperammonemia (urea cycle enzyme deficiency) treatment

Answer 10

restrict dietary protein
replace essential aa w/ alpha-ketoacids
sterilization of GI tract with antibiotics or mannose
BENZOIC ACID AND PHENYLACETIC ACID
(these make hippuric acid which is an alternative path of nitrogen excretion)