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EOM Test 4 > Urea Cycle > Flashcards

Urea Cycle Flashcards

1
Q

What is responsible for generating over half of the total body pool of free amino acids?

A

Skeletal muscle

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2
Q

What structures take up free glutamine from circulation and excrete alanine?

A

Gut and Kidney

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3
Q

Describe the glucose-alanine cycle.

A

Alanine is synthesized in the muscle via transamination of pyruvate

Alanine is transported to the liver via circulation

Alanine is reconverted into glucose in the liver via gluconeogenesis

Glucose is transported back to the muscle

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4
Q

What are the four stages of Urea biosynthesis?

A

1) Transamination
2) Oxidative deamination of glutamate
3) Ammonia Transport
4) Reactions of the urea cycle

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5
Q

What is the function of transamination reactions?

A

Introconvert pairs of a-amino acids and a-keto acids

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6
Q

What is the cofactor for transaminases and what is its role?

A

Pyridoxal phosphate (Vit. B6)

Serves as a carrier of amino groups during transamination

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7
Q

What four amino acids don’t participate in transamination?

A

Lysine

Threonine

Proline

Hydroxyproline

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8
Q

The a-amino nitrogen from all amino acids that undergo transamination can be concentrated into what amino acid and why is this important?

A

Glutamate

Glutamate is the only amino acid that undergoes oxidative deamination at an appreciable rate in mammalian tissues

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9
Q

What is the function of glutamate dehydrogenase?

A

Catalyzes the deamination of glutamate to a-ketoglutarate, releasing NH3

NAD+ or NADP+ Can serve as the oxidoreductant

This reaction is reversible strongly favors glutamate formation

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10
Q

How is glutamate dehydrogenase regulated?

A

Stimulated: ADP

Inhibited: ATP, GTP, and NADH

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11
Q

What is the function of glutamine synthase?

A

Formation of glutamine in the mitochondria from glutamate and free Ammonia

ATP-dependent

Plays a major role in ammonia detoxification

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12
Q

What is the function of glutaminase and Asparaginase?

A

Deamidate Glutamine and Asparagine

Liver and Renal isoforms

Renal isoforms upregulated and downregulated during metabolic acidosis and alkalosis respectively

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13
Q

What is the function of Carbamoyl Phosphate Synthase I?

A

Condensation of CO2, Ammonia, and ATP to form carbamoyl phosphate

Rate-limiting step of the urea cycle

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14
Q

What is the function of N-acetylglutamate?

A

Allosteric activator of CPS I that enhances its affinity for ATP

CPS I is only active when this is present

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15
Q

Why does synthesis of 1 mol of carbamoyl phosphate need 2 mol of ATP?

A

One ATP serves as the phosphoryl donor

One ATP serves as the driving force for amide bond formation

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16
Q

What is the function of Ornithine transcarbamoylase?

A

Catalyzes the transfer of the carbamoyl group of carbamoyl phosphate to ornithine

Forms Citrulline and orthophosphate

17
Q

What is the function of Argininoscuccinate Synthase?

A

Links aspartate and citrulline, forming argininosucinate

ATP-dependent

18
Q

What is the function of Argininosuccinate lyase?

A

Cleave of argininosuccinate to form arginine and fumarate

19
Q

What is the function of Arginase?

A

Cleaves Arginine to release ornithine and urea

Inhibited by ornithine and lysine

20
Q

What two reactions of the urea cycle occur in the mitochondrial matrix?

A

CPS I

Ornithine carbamoyl transferase

21
Q

What amino acid is transported into the mitochondria for use in the urea cycle?

A

Ornithine

22
Q

What amino acid is transported out of the mitochondria during the urea cycle?

A

Citrulline

23
Q

How is N-acetylglutamate synthesized?

A

Acetyl-CoA and glutamate

24
Q

Where does the nitrogen come from that is released in urea?

A

Ammonia and Aspartate

25
Q

How do Aspartate and Fumarate link the TCA cycle and the urea cycle?

A

Fumarate produced by argininosuccinate lyase is a TCA cycle intermediate

Transamination of oxaloacetate produces aspartate

26
Q

How do you treat urea cycle defects?

A

Bypassing blocked steps by providing intermediates

EOM Test 4 (19 decks)

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