Urea cycle

Question 1

Step 1

Answer 1

enzyme: carbamoyl phosphate synthetase

purpose: to form carbamoyl phosphate from bicarbonate and ammonia

Question 2

Step 2

Answer 2

enzyme: ornithine trans-carbamoylase

purpose: to transfer carbamoyl group to orthinine to produce citrulline which is then transported to the cytoplasm

Question 3

Step 3

Answer 3

enzyme: argininosuccinate synthetase

purpose: to condence citrulline with aspartate to produce arignino-succinate

Question 4

Step 4

Answer 4

enzyme: argininosuccinase

purpose: to separate asp carbon skeleton by cleaving off fumarate and leaving argining

Question 5

Step 5

Answer 5

enzyme: arginase

purpose: to hydrolyze arg side chain to produce urea and regenerate ornithine

Question 6

Ala and gln produced during amino acid breakdown

Answer 6

act as transporters to move excess NH3 to the liver
both are converted to glutamate in the liver by glutaminase or transaminase

Question 7

NH3 is released as

Answer 7

ammonia

Question 8

How is the second NH3 group on urea produced

Answer 8

glu can transfer its NH3 to oxaloacetate through a transaminase reaction, producing asp which produces the second NH3 group

Question 9

How is the urea cycle regulated

Answer 9

1. carbamoyl phosphate synthetase is allosterically activated by N-acetylglutamate (NAG)
2. Glu buildup occurs during amino acid breakdown which stimulates NAG production. this activates CPSI to dispose of excess amino groups

Question 10

How is N-acetylglutamate produced

Answer 10

enzyme: N-acetylglutamate synthase

materials needed: acetyl-coa and glutamate

Question 11

What is the committed step of the urea cycle

Answer 11

step 1