Urea Cycle

Question 1

Function

Answer 1

too much nitrogen -> urea
detoxification
excretion

Question 2

1. CO2 + NH4 -> Carbamoyl Phosphate

Answer 2

2ATP - 2ADP + H2O
enzyme: CARBAMOYL PHOSPHATE SYNTHETASE 1
1st committed step

Question 3

2. Ornithine + Carbamoyl P -> Citrulline

Answer 3

• P

enzyme: ORNITHINE TRANSCARBAMOYLASE

Question 4

3. Citrulline -> Citrulline-AMP

Answer 4

ATP->PPi

enzyme: ARGINOSUCCINATE SYNTHETASE

Question 5

4. Citrulline-AMP -> Arginosuccinate

Answer 5

+Asp

• AMP
  enzyme: ARGINOSUCCINATE SYNTHETASE

Question 6

5. Arginosuccinate -> Arginine

Answer 6

• fumarate

enzyme: ARGINOSUCCINASE

Question 7

6. Arginine -> Orithine

Answer 7

+H2O

• urea (excreted)
  enzyme: ARGINASE

Question 8

Transporters

Answer 8

Ornithine transporter: ornithine from cytosol to mito matrix

Citrulline transporter: citrulline from mitomatrix to cytosol

Question 9

Long term regulation

Answer 9

high N flux -> increase enzyme synthesis - increase urea
low N flux -> decrease synthesis - decrease urea
high protein in diet - increase urea
low protein in diet - decrease urea
starvation -> increase urea

Question 10

Regulation of Carbamoyl Phosphate synthetase 1

Answer 10

+ N-acetylglutamate

+arginine (activated N-acetylglutamate synthase enzyme)

Question 11

Net reaction of urea cycle

Answer 11

Aspartate + NH3 + CO3 + 3ATP + H2O -> urea + fumarate + 2ADP + AMP + 2Pi + PPi