CR III - Urea Cycle

Question 1

What is the only way to rid ammonia from the blood?

Answer 1

Alpha-ketoglutarate -> Glutamate -> Glutamine

Question 2

What does increased NH4+ in astrocytes lead to in regards to K?

Answer 2

Elevated excellular K
Na-Cl-K transporter brings K in
Excess Cl alters response to GABA leading to seizures

Question 3

How do plants, aquatic species, terrestrial vertebrates, and birds handle nitrogen excretion?

Answer 3

Plants - conserve
Aquatic species - release into water
Terrestrial - urea
Birds - uric acid

Question 4

What does carbomoyl phosphate synthase I do? Where?

Answer 4

Converts ammonia to carbamoyl phosphate

In mitochondria

Question 5

Which product in the urea cycle can leave the mitochondria? What enzyme creates it?

Answer 5

Citrulline

Ornithine trans-carbamoylase

Question 6

After citrulline enters the cytosol, what are the next 3 products in the cycle?

Answer 6

Arginosuccinate
Arginine
Ornithine

Question 7

What enzyme converts citrulline to argininosuccinate? How many moles of this enzyme is used? What contributes the 2nd amino group at this step?

Answer 7

Argininosuccinate synthase
2 mols
Aspartate

Question 8

What enzyme converts arginosuccinate to arginine? What is a byproduct at this step?

Answer 8

Arginoinosuccinase

Fumarate

Question 9

What converts arginine to orthinine? What is the major byproduct at this step?

Answer 9

Arginase

Urea

Question 10

How many ATP are used in the urea cycle? How are 2.5 regained?

Answer 10

4

By malate transporter, generating an NADH

Question 11

With all cycles considered, what two things come into matrix? What two things leave the mitochondrial matrix?

Answer 11

In - malate and glutamate

Out - Aspartate and alpha-ketoglutarate

Question 12

What is malate converted to in the mitochondrial matrix to produce an NADH?

Answer 12

Oxaloacetate

Question 13

What enhances carbomoyl phosphate synthase I? How? What enhances the enhancer formation from acetyl-CoA and glutamate?

Answer 13

N-acetylglutamate
Allosterically
Arginine - enhances the synthesis of the enhancer

Question 14

What is hyperammonemia?

Answer 14

Absence of enzyme in urea cycle, causing build up

Question 15

What two things can be administered to reduce ammonia levels in the blood?

Answer 15

Aromatic acids benoate or phenylbutyrate

Question 16

If someone is deficient in the enzymes in the urea cycle, what dietary supplement could be given?

Answer 16

Arginine

Question 17

Deficiency of N-acetylglutamate synthase resulting in absent carbamoyl phosphate synthetase I can be treated by administering what?

Answer 17

Carbamoyl glutamate

Question 18

The urea cycle results in net conversion of _____ to _____, both of which are itnermediates in the citric acid cycle?

Answer 18

Oxaloactate

Fumarate