Lecturio - Urea Cycle Flashcards by Aurora H

Q

Nitrogen is needed for synthesis of ___

A

1/ Nucleotides (ATP, GTP, CTP, UTP, dATP, dCTP, dGTP, dTTP)
2/ Non protein AAs (Ornithine, Citrulline, Sarcosine)
3/ Other nitrogen-containing compounds (choline, carnitine, and vitamins)

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Q

Solubility of ammonia. Why?

A

1 nitrogen, water soluble and toxic

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Q

Solubility of urea. Why?

A

2 nitrogens, very water soluble

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Q

Solubility of uric acid. Why?

A

4 nitrogens, not very water soluble

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Q

Uric acid is produced by ____

A

purine catabolism

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Q

Urea is produced by ____

A

urea cycle

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Q

The Central Role of Glutamate
-> Identify

A

Glutamic acid

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Q

The Central Role of Glutamate
-> Identify

A

α-ketoglutaric acid

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Q

The Central Role of Glutamate
-> Identify

A

1/ Glutamine synthetase
2/ Glutamine transaminase

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Q

The Central Role of Glutamate
-> Identify

A

Glucose-alanine cycle

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Q

Location of urea cycle?

A

Primarily occurs in liver; also in kidney

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Q

What does urea cycle contain?

A

Consists of 4 cycle reactions and 1 feeder reaction

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Q

What does urea cycle contain?

A

Consists of 4 cycle reactions and 1 feeder reaction

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Q

The role of Feeder reaction in Urea Cycle?

A

It incorporates 1 molecule of ammonia and 1 CO2 per turn.

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Q

The role of Cycle reaction in Urea Cycle?

A

It provides 1 amine from an amino acid.

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Q

Output of Urea cycle is ____ per turn

A

1 molecule of urea

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Q

The net reaction per turn of the UREA cycle is:

A

2NH3 +CO2 +3ATP+H2O -> urea + 2ADP + 4Pi +AMP

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Q

urea cycle
-> Identify

A

NH4+ + HCO3-

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Q

Urea Cycle
-> Identify

A

Urea

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Q

Urea Cycle
-> Identify

A

1/ Carbamoyl phosphate synthetase
2/ Ornithine Transcarbamoylase
3/ Argininosuccinate Synthetase
4/ Argininosuccinate Lyase
5/ Arginase

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Q

What is the source of ammonium ion in urea cycle?

A

The source of ammonium ion is glutamine or glutamate

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Q

The source of ammonium ion is glutamine or glutamate.
=> The reaction require which enzyme(s)?

A

The reaction requires action of glutaminase (glutamine) or glutamate dehydrogenase (glutamate).

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Q

Carbamoyl Phosphate Synthetase Reaction
-> What is the net reaction?

A

2 ATP + HCO3 + NH4+ <=> 2 ADP + carbamoyl phosphate + P

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Q

Carbamoyl Phosphate Synthetase Reaction
-> Identify

A

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Identify these molecules

Identify the enzyme for this reaction

Ornithine transcarbamoylase

Ornithine Transcarbamoylase Reaction -> Ornithine Transcarbamoylase is expressed only in ___

liver

Ornithine Transcarbamoylase Reaction -> What is the inheritance pattern of this enzyme?

X-linked

Ornithine Transcarbamoylase Reaction -> What are the most common treatments for the deficiency of Ornithine Transcarbamoylase?

1/ Low protein diet 2/ Liver transplant

In urea cycle, which enzyme is the most commonly deficient enzyme?

Ornithine transcarbamoylase

What is the alternative way to produce Citrulline? (except using Ornithine transcarbamoylase)

By using Nitric oxide synthase

How is nitric oxide synthetase used to produce citrulline

Alternate means of producing citrulline nitric oxide synthase -> What is the substrate for reaction?

Arginine

Citrulline movement to cytoplasm requires ____

ornithine-citrulline translocase

Citrulline movement to cytoplasm requires ornithine-citrulline translocase -> Characteristics of this transporter

Antiport moves citrulline out, ornithine in -> Needed for both parts of urea cycle (mitochondrial and cytosol)

Citrulline movement to cytoplasm requires ____

ornithine-citrulline translocase

Identify

1/ Citrulline 2/ Ornithine

What are the 2 step reaction of Argininosuccinate Synthetase?

* First, AMP attaches to amine-rich end of citrulline * Next, aspartate displaces the AMP

Argininosuccinate Synthetase -> What is happening at 1?

First, AMP attaches to amine-rich end of citrulline

Argininosuccinate Synthetase -> What is happening at 2?

aspartate displaces the AMP (Two step reaction * First, AMP attaches to amine-rich end of citrulline * Next, aspartate displaces the AMP)

What is the product of Argininosuccinate Synthetase?

The product is L-argininosuccinate.

Which reaction in urea cycle is the rate-limiting step?

Reaction catalyzed by Argininosuccinate Synthetase

Argininosuccinate Synthetase -> Gene expression of enzyme reduced by (1)____, increased by (2)____

1/ arginine 2/ citrulline

Argininosuccinate Synthetase defects lead to ____

citrullinemia - accumulation of ammonia

Argininosuccinate Synthetase defects lead to citrullinemia - accumulation of ammonia -> What are the most common treatments?

Treated with low protein diet, arginine supplementation

Argininosuccinate Lyase important for production of ____

arginine

Argininosuccinate Lyase reaction -> Identify

1/ Argininosuccinic acid 2/ Arginine 3/ Fumaric acid

Identify the enzyme catalyzed this reaction

Arginosuccinate lyase

In Urea Cycle, which reaction is the source of fumarate?

Reaction catalyzed by Argininosuccinate Lyase

UREA CYCLE In Argininosuccinate Lyase reaction, what is the fate of arginine?

To proteins or remainder of urea cycle

UREA CYCLE In Argininosuccinate Lyase reaction, what is the fate of fumarate?

To citric acid cycle

Identify these molecules

1/ Arginine 2/ Urea 3/ Ornithine

Identify the enzyme

Arginase

Arginase is co-expressed with ____

nitric oxide synthase in smooth muscle

Arginase -> Increased arginase activity reduces____

nitric oxide production.

Arginase -> The role of Nitric oxide

Nitric oxide relaxes smooth muscle and facilitates erection of penis.

In urea cycle, what is the fate of urea?

Excretion

In urea cycle, what is the fate of Ornithine?

To mitochondria to complete cycle through Ornithine citrulline translocase

Carbamoyl phosphate synthetase I deficiency -> Accumulating molecules?

Ammonia

Ornithine transcarbamylase deficiency -> Accumulating molecules?

Ornithine, uracil, orotic acid

Citrullinemia -> Enzyme deficiency? Accumulating molecules?

Enzyme - Argininosuccinate synthetase Accumulating molecules - Citrulline

Argininosuccinic aciduria -> Enzyme deficiency? Accumulating molecules?

Enzyme - Argininosuccinate lyase Accumulating molecules - Citrulline, arginiosuccinic acid

Argininemia -> Enzyme deficiency? Accumulating molecules?

Enzyme - Arginase Accumulating molecules - Arginine