urea cycle

Question 1

what transports NH4 in the bloodstream

Answer 1

glutamine

Question 2

glutamine synthase

Answer 2

cataylyzes the combination of free ammn=onia with glutamate to yield glutamine
requires ATP
-is critical to transport toxic ammonia to the liver

Question 3

glutaminase

Answer 3

catalyzes the conversion of glutamine to glutamate and NH4

Question 4

glycose alanine cycle

Answer 4

skeletal muscles produce pyruvate, lactate, and ammonia

alanine carries ammonia and carbon skeleton from pyruvate to liver
-ammonia is excreted
-pyruvate is used to produce glucose which is returned to muscle

Question 5

alanine aminotransferase

Answer 5

intervonverts pyruvate and alanine via transamination with glutamate

Question 6

five enzymatic steps of urea production form ammonia

Answer 6

1. carbamoyl phosphate synthetase I
2. ornithine trascarbamoylase
3. agrininosuccinate synthase
4. argininosuccinase
5. arginase

Question 7

carbamoyl phsphate synthetase I

Answer 7

brings in ammonia from deamination reactions

Question 8

ornithine trascarbamoylase

Answer 8

brings carbamoyl phsophate into the urea cycle resulting in citrulline which can enter the cytosisol
also forms Pi from ornithine and carbamoyl phosphate

Question 9

argininosuccinate synthetase

Answer 9

brings in the second amino group from aspartate
catalyzes the condensation of the amino group of aspartate and the ureido group of citrulline
-requires ATP
-uses an intermediate

Question 10

argininosuccinase

Answer 10

removes length of carbon skeleton as fumarate
catalyzes reversible cleavage of argininosuccinate from arginine and fumarate
-fumarate is converted to malate and joins the pool of cirtic acid cycle intermedites

Question 11

arginase

Answer 11

cleavage of arginine to form urea and ornithine - back at begining of cycle
-ornithine formed is transported into mitochondrion to initiate another round

Question 12

rate limiting step of urea cycle

Answer 12

carbamoyl phsophate sythetase I reaction
-has two activation steps that require ATP
-second step of reaction uses ammonia from deamination reaction

Question 13

what happens during the formation of argininosuccinate

Answer 13

cirtrulline passes from mitochondrion to cytosol

Question 14

aspartate arginosuccinate shunt

Answer 14

pathways linking the citric acid cycle and urea cycle
-link the fates of the amino groups and the carbon skeletons of amino groups

Question 15

regulation of the activity of the urea cycle

Answer 15

occurs at two levels
1. level of enzyme synthesis for urea cycle enzymes and carbamoyl phosphate synthetase I
2. allosteric regulation of carbamoyl phosphate syntehtase I

Question 16

N acetylglutamate synthase

Answer 16

catalyzes formation of N acetylglytamate from acetyl CoA and glutamate

Question 17

what does N acetylglutamate do

Answer 17

allosterically activates carbamoyl phosphate synthetase I