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CMBM exam 4 > Urea Cycle > Flashcards

Urea Cycle Flashcards

1
Q

What does glutamate synthase transfer to a-ketoglutarate?

A

Nitrogen

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2
Q

Glutamine is the ____ carrier.

A

Nitrogen

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3
Q

What are the three fates of ammonium?

A

Glutamate dehydrogenase
Glutamine synthase
Carbamoyl-phosphate synthase I

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4
Q

What happens in the reactions containing glutamate dehydrogenase and glutamate synthase?

A

Reductive amination of a-ketoglutarate to form glutamate

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5
Q

What happens in the reaction containing glutamine synthetase?

A

ATP-dependent amidation of gamma-carboxyl of glutamate

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6
Q

What happens in the reactions containing carbamoyl-phosphate synthase I?

A

2 ATP are required

1 activates bicarbonatem which the other phosphorylates carbamate

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7
Q

Why would the body want to have NH3 when it could be the more relevant NH4+?

A

NH3 is the form that can cross cell membranes

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8
Q

What is the breakdown of animo acids from food called and how does it work?

A

Transamination

Swap NH3 group for a different keto-acid

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9
Q

What is transamination?

A

Transfer of an amino group from an a-amino acid to an a-keto-acid

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10
Q

In amino acid biosynthesis, the amino acid glutamate is transferred to various _____ which generates _____.

A

a-keto acids, a-amino acids

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11
Q

What two amino acids are generated in mino acid catabolism?

A

Glutamate or aspartate

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12
Q

What are the essential amino acids?

A

Histidine, Isoleucine, Leucine, Methionine, Phenylalanine, Threonina, Tryptophan, Valine, Lysine

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13
Q

What is nitric oxide?

A

NO is a gas hormone which can diffuse into cells and is a messenger that activates guanylyl cyclase (cGMP synth)

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14
Q

What is NO synthesized from?

A

Arginine

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15
Q

What are the actions of NO?

A

Relaxes blood vessels, lowers blood pressure and is a neurotransmitter in the brain

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16
Q

What is converted into NO to dilate coronary arteries?

A

Nitroglycerin

17
Q

When the body is in starvation, what are degraded to amino acids for glucose?

A

Proteins

18
Q

What are the glucogenic animo acids?

A

Ala, Ser, Cys, Thr, Trp, Asp, Arg, Phe, Ile, Met, Val

19
Q

What are the ketogenic amino acids?

A

Ile, Leu, Thr, Trp, Leu, Lys, Phe, Tyr

20
Q

What process does the muscle eliminate nitrogen to replenish energy?

A

Indirectly due to the exchange of glucose and alanine

21
Q

Which types of animo acids are the first to be catalyzed for these pathways?

A

Branched-chain (Leucine, Valine and Isoleucine)

22
Q

Which intermediate of amino acid breakdown also is used in the formation of ketone bodies?

A

HMG-CoA

23
Q

In the study of branched-chain amino acids, what is the key to understanding the relationship between dietary protein and carbohydrates?

A

Understnading the relationship between branched-amino acids, insulin and glucose metabolism

24
Q

What is a major gluconeogenic amino acid and what happens to it when it enters the liver?

A

Alanine and it becomes urea

25
Q

When a transamination reactions happen what is used as the enzyme and cofactor in the reverse reactions?

A

Transaminases/ aminotransferases and pyridoxal phospahte (PLP)

26
Q

Which is the only reversible step of the urea cycle?

A

Glutamate dehydrogenase (GDH)

27
Q

What is the link between the TCA and Urea cycle?

A

Fumarate

28
Q

What is the role of glutamate in urea production?

A

Collects nitrogen from other amino acids by transamination reactions and is released as NH4+ by glutamate dehydrogenase

29
Q

What is the first step of the urea cycle?

A

NH4+, bicarbonate and ATP react to form carbamoyl phosphate catalyzed by carbamoyl phosphate synthase I (CPSI)

30
Q

Where would you find carbamoyl phosphate synthase II and what does it do?

A

In the cytosol and produced carbamoyl phosphate for pyrimidine biosynthesis, using nitrogen from glutamine

31
Q

When you combine citrulline and aspartate via arginosuccinate synthase what do you get?

A

Arginosuccinate

32
Q

What gets release by arginosuccinate lyase to make arginine?

A

Fumarate

33
Q

The higher the rate of ammonia production, the _____ the rate of urea formation.

A

Higher

34
Q

What type of regulation is the urea cycle?

A

Feed forward

35
Q

What are the other two types of regulation that can control the urea cycle?

A

Allosteric activation of CPSI by N-acetylglutamate (NAG)

Induction/repression of the synthesis of urea cycle enzyme

36
Q

During fasting is urea excretion high or low?

A

High

37
Q

When the something happen to the urea cycle and it stop working correctly, what is the key factor in ammonia build up?

A

a-ketoglutarate cannot be regenerated ledaing to an inc in glutamine and thus cannot fix free ammonia

38
Q

Which drugs can be used to form conjugates with amino acids in the case of urea cycle deficits?

A

Benzoic acid and phenylbutyrate

39
Q

Which enzyme deficiency of the urea cycle is thought to be genetically linked?

A

Ornithine transcarbamoylase

CMBM exam 4 (27 decks)

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