Lecture 23 - Detoxification of Ammonia: Urea and Glutamine Synthesis

Question 1

Glutamine is a nontoxic transporter of the __________ ion from extrahepatic tissue to the liver.

Answer 1

ammonium

Question 2

Excess glutamine is degraded in the liver to a-KG and NH4+, where the ammonia is converted to:

Answer 2

urea

Question 3

Glutamate is converted to glutamine by the _____________ enzyme using ATP.

Answer 3

glutamine synthetase

Question 4

Glutamate is converted to glutamine in the cytosol of all tissues, but especially ______.

Answer 4

the brain (!)

Question 5

Which type of hepatocytes are found near the portal vein of the liver?

Answer 5

periportal hepatocytes

Question 6

Which type of hepatocytes are found near the central vein of the liver?

Answer 6

perivenous hepatocytes

Question 7

Which is found in the mitochondria of periportal hepatocytes?

A. CPS-I
B. CPS-II
C. Glutamine synthetase

Answer 7

A

Question 8

Which is found in the cytosol of perivenous hepatocytes?

A. CPS-I
B. CPS-II
C. Glutamine synthetase

Answer 8

C

Question 9

__________ is allosterically activated by ammonium ions.

A. CPS-I
B. CPS-II
C. Glutamine synthetase
D. Glutaminase

Answer 9

D

Question 10

What are the two precursors of the nitrogen atoms in the urea?

Answer 10

1. aspartate

2. ammonium ion

Question 11

The carbon and oxygen atoms (in the form of a carbonyl group) in urea come from a _______ ion.

Answer 11

bicarbonate

Question 12

What are 3 properties of urea that make it a good physiologic choice as a molecule for disposal of waste nitrogen?

Answer 12

1. Nontoxic product
2. Dissolves easily in water - polar
3. Easy to synthesize (low energy cost)

Question 13

Both ureagenesis and gluconeogenesis happen in the _____.

Answer 13

liver

Question 14

The energy cost for synthesizing each molecule of urea is:

Answer 14

4 high energy phosphate bonds

Question 15

_________ from skeletal muscle is used to transport ammonia for ureagenesis to the liver, and then is used to regenerate pyruvate in the liver.

Answer 15

Alanine

Question 16

Hyperammonemia Type I is a defect in:

A. CPS-I
B. OTCase
C. Argininosuccinate synthase
D. Argininosuccinate lyase

Answer 16

A - Hyperammonemia Type I is low plasma citrulline, LOW urinary orotate.

Question 17

Hyperammonemia Type II is a defect in:

A. CPS-I
B. OTCase
C. Argininosuccinate synthase
D. Argininosuccinate lyase

Answer 17

B - Hyperammonemia Type II is low plasma citrulline, HIGH urinary orotate.

Question 18

Citrullinemia is a defect in:

A. CPS-I
B. OTCase
C. Argininosuccinate synthase
D. Argininosuccinate lyase
E. Arginase

Answer 18

C - citrullinemia is high plasma citrulline.

Question 19

Argininosuccinic aciduris is a defect in:

A. CPS-I
B. OTCase
C. Argininosuccinate synthase
D. Argininosuccinate lyase
E. Arginase

Answer 19

D - Argininosuccinic aciduris is medium plasma citrulline, argininosuccinate, and anhydrides in plasma.

Question 20

_______ is low plasma citrulline and high urinary orotate.

A. Hyperammonemia Type I
B. Hyperammonemia Type II
C. Citrullinemia

Answer 20

B

Question 21

Short term regulation of the urea cycle is exerted at the level of what enzyme?

Answer 21

carbamoyl phosphate synthetase I (CPS-I)

Question 22

Long term regulation of the urea cycle depends on changes in the levels of ____________.

Answer 22

urea cycle enzymes

Question 23

Both benzoate and phenylacetate promote alternative pathways of ______.

Answer 23

nitrogen elimination