urea cycle

Question 1

Trapping ammonia into urea (transamination): 3 steps

Answer 1

1. Transferring amino group from AA to alpha ketogluterate, producing alpha ketoacid and glutamate (containing the nh2 group)
2. glutamate transferring nh2 to nad+ producing
3. Nadh and NH4
4. NADH + NH4
5. NH4 enters urea cycle

Question 2

Where does the urea cycle occur?

Answer 2

in the liver?

Question 3

1st step in urea synthesis

____ + ____ —> _______

Answer 3

CO2 + NH4 —> carbamoyl phosphate

          C=O attached to a O3PO and NH2

Question 4

Where do the atoms in the carbamoyl phosphate come from?

Answer 4

CO2 metabolism, and NH4 from deamination

Question 5

What is the enzyme responsible for transferring CO2 to NH4?

Answer 5

carbomyl phosphate synthetase

Question 6

2nd step in urea cycle

Answer 6

combining carbomyl phosphate with ornithine to produce citrulline

Question 7

Where does the 2nd step occur?

Answer 7

mito

Question 8

Where does the 1st step occur?

Answer 8

mito

Question 9

T/F citrulline can be located in both the mito and the cytoplasm?

Answer 9

True

Question 10

3rd step in urea cycle

Answer 10

Citrulline is combined with aspartate to produce argininosuccinate

Question 11

Argininosuccinate is the product of

Answer 11

aspartate and citrulline

Question 12

What does aspartate contribute to the urea cycle

Answer 12

-NH2

Question 13

What catalyzes the formation of argininosuccinate?

Answer 13

argininosuccinate synthase

Question 14

argininosuccinate —->

Answer 14

Arginine and Fumarate

Question 15

What enzymes catalyze the 1st, 2nd, 3rd, 4th, 5th steps in the urea cycle?

Answer 15

1. Carbamoyl phosphate synthetase (CPS1)
2. Ornithine transcarbamolyase (OTC)
3. Argininosuccinate synthetase
4. Argininosuccinate lyase
5. Argininase (breaks arginine into ornithine and urea)

Question 16

Where does transamination occur?

Answer 16

muscle

Question 17

The nitrogen for the urea cycle comes from where?

Answer 17

funneled from transamination reactions

Question 18

What is the significance of aspartate and fumarate in the urea cycle? What happens to the two?

Answer 18

Fumarate —> malate–> oxaloacetate –> aspartate and glucose (if it wishes)

Question 19

What are the two “funneling” events of ammonias?

Answer 19

1. coming from glutamate in transamination reactions
2. coming from aspartate from TCA cycle

Transamination rxns = glutamate or aspartate

Question 20

Fumerate –>

Answer 20

aspartate

Question 21

transamination rxns =

Answer 21

amino acids funnel amino groups by transamination reactions generating aspartate or glutamate

glutamate releases free ammonia
aspartate releases it directly into urea cycle

Question 22

“Funneling” by transaminations come from

Answer 22

muscle: exercise causes high protein degradation producing alanine

alanine goes to the liver

Question 23

which amino acid is the most produced by muscle and brain, and transferred to the liver?

Answer 23

alanine