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Biochemistry > Urea Cycle > Flashcards

Urea Cycle Flashcards

1
Q

________ is a chemical reaction between two molecules. One is an amino acid, which contains an amine (NH2) group. The other is a keto acid, which contains a keto (=O) group.

A

Transamination

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2
Q

______ is the removal of an amine group from a molecule. Enzymes that catalyse this reaction are called deaminases

A

deamination

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3
Q

____ is deaminated in the kidneys, but the majority of things are deaminated in the ______

A

glutamate, liver

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4
Q

over 90% of nitrogen excretion is in the form of ______

A

urea

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5
Q

________ is the degradation product of purine bases

A

uric acid

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6
Q

list four purine bases

A

adenine, guanine, hypoxanthine and xanthine

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7
Q

______ is released from glutamate, especially by the _____

A

ammonia, kidneys

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8
Q

NH3

A

ammonia

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9
Q

____ is a very important ion for pH control and buffering of urine

A

ammoium ions (NH4+)

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10
Q

transamination rxns are catalyzed by transaminsases, aka ______

A

aminotransferases

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11
Q

_____ is an enzyme that catalyzes a type of reaction between an amino acid and an α-keto acid.

A

transaminases/aminotransferases

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12
Q

what is the major cofactor for transamination rxns?

A

pyridoxal phosphate

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13
Q

what are the 3 transamination pairs?

A

asparate & oxaloacetate,
glutamate & alpha-ketoglutarate,
alanine & pyruvate

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14
Q

pyridoxal phosphate (PLP) is derived from _______

A

Pyridoxine (vit B6)

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15
Q

all AA except what 3 can undergo transamination?

A

lysine, threonine, proline

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16
Q

for almost all reactions the ____________ pair serves as one of the alpha-keto AA pairs

A

alpha-keotglutarate - glutamate

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17
Q

is transamination reversible?

A

yes

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18
Q

____ is the transaminase that present in the cytoplasm of liver cells

A

alanin transaminase (ALT) aka as glutamic pyruvic transaminase - GPT

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19
Q

____ is the transaminase that present in liver, heart, and skeletal muscle

A

aspartate transaminase (AST) aka as glutamic oxalacetic transaminase-GOT

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20
Q

damage to specific organs will result in an increase of serum levels of what?

A

ALT and AST (corresponding to the organ)

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21
Q

describe the first rxn of the urea cycle

A

ammonium ions (NH4+) are rapidly converted to carbomoyl phosphate, this occurs in the mitochondria

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22
Q

what are the allosteric inhibitor of glutamate dehydrogenase (GDH) for oxidative deamination

A

high ATP, GTP, and NADH

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23
Q

what is glutamate dehydrogenase?

A

it is an enzyme that catalyzes oxidate deamination between glutamate and alpha-ketoglutarate, which releases ammonium

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24
Q

which amino acid is known as the “gate-way” amino acid and why?

A

glutamate, it always serves as one of the amino acids in transaminations

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25
Q

where does oxidative deaminatio by L-amino acid oxidase mainly occur?

A

in the liver and kidneys

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26
Q

what cofactor is needed for oxidative deaminatio by L-amino acid oxidase?

A

FMN (flavin mononucleotide)

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27
Q

ammonium ions produced by non-oxidative deamination in non-hepatic tissues are transported to the liver in the form of what 3 possible things?

A

glutamate, glutamine, or alanine

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28
Q

name the non-oxidative dehydration enzymes

A

Serine dehydratase,
Threonine dehydratase,
D-cysteine desulfhydrase

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29
Q

name the non-oxidative hydrolytic enzymes

A

Glutaminase & Asparaginase

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30
Q

Free ammonium ions in nonhepatic tissue are primarily detoxified by what enzyme?

A

glutamine synthetase

31
Q

glutamine synthetase make glutamine which then carries free ammonium ions to the liver for final conversion to what?

A

urea

32
Q

what enzyme is especially important in the kidney whose main function is the production of ammonia for acid-base regulation

A

glutaminase

33
Q

______ is a major amino acid of circulation; its role is to ferry ammonia to and from various tissues

A

glutamine

34
Q

In kidney, glutamine is hydrolyzed by ______ releasing the ammonia to the urine

A

glutaminase

35
Q

when does the liver divert ammonia to glutamine, then the kidney converts to a-ketoglutarate yields 2 NH4+ which reduces the H+ concentration.

A

under acidotic conditions

36
Q

(T/F) Humans are totally dependent on other organisms for converting atmospheric nitrogen into forms available to the body

A

true

37
Q

what is the primary source of nitrogen metabolized by the body?

A

dietary proteins

38
Q

is ATP required for the urea cycle?

A

yes

39
Q

where does the formation of carbamoyl phosphate occur?

A

the mitochondria

40
Q

how many nitrogens does aspartate provide?

A

one

41
Q

____ is released from arginine in a reaction catalyzed by _____

A

urea, arginase

42
Q

In the liver, the ammonia produced from what 3 things is converted to urea through urea cycle?

A

Glutamate, from AMP, or by direct deamination

43
Q

Carbon dioxide and ammonium ion react with two molecules of ATP to form _____

A

carbamoyl phosphate

44
Q

what 3 things react to form carbomoyl phosphate?

A

Carbon dioxide and ammonium ion react with two molecules of ATP

45
Q

____ or _____ can serve as the cofactor for glutamate dehydrogenase (GDH)

A

NAD+ or NADP+

46
Q

CPS1

A

Carbamoyl phosphate synthetase

47
Q

in the 2nd rxn of the urea cycle, Carbamoyl phosphate reacts with ______ to form ______, which moves out of the mitochondrion into the cytoplasm.

A

ornithine, citrulline

48
Q

what are 2 major promoters of the urea cycle?

A

NH4+ and glutamate

49
Q

the ctivation of carbamoyl phosphate synthetase I (CPSI) requires what precursors?

A

glutamate and acetyl CoA react with arginine to for N-acetyl glutamate

50
Q

describe the second rxn in the urea cycle

A

carbamoyl phosphate and ornithine are catalyzed by ornithine transcarbamoylase to form citrulline

51
Q

describe the 3rd rxn of the urea cycle

A

citrulline and aspartic acid are catalyzed by arginosuccinate synthetase to form arginosuccinate

52
Q

where do the rxns 3-5 of the urea cycle take place?

A

in the cytoplasm

53
Q

describe the 4th rxn of the urea cycle

A

arginosuccinate is catalyzed by arginosuccinate lyase to form arginine and fumurate

54
Q

describe the 5th and last rxn of the urea cycle

A

arginine is gatalyzed by arginase to form ornithine and urea

55
Q

Carbamoyl phosphate synthetase (CPS) is dependent on ________ for activity

A

N-acetylglutamate

56
Q

Synthesis of N-acetylglutamate is catalyzed by _________

A

N-acetylglutamate synthetase

57
Q

_____ is an allosteric activator of N-acetylglutamate synthetase

A

Arginine

58
Q

Defects in urea cycle result in what?

A

accumulation of ammonia in the blood

59
Q

All of the deficiencies of components needed for the urea cycle may present with _______

A

hyperammonemia

60
Q

define hyperammonemia

A

a metabolic disturbance characterised by an excess of ammonia in the blood

61
Q

brain damage, coma, and death due to lack of ATP, neural defects, and the depletion of glutamate stores needed to make GABA (the neurotransmitter) are all results of what?

A

ammonia intoxification

62
Q

(T/F) glutumate can readily cross the BBB

A

False, it cannot cross the BBB

63
Q

what are the 3 possible Tx’s for defects in the urea cycle enzymes?

A

limit protein intake, remove excess ammonia, and replace missing intermediates from the cycle

64
Q

what two things can be used to remove excess ammonia from the blood stream?

A

sodium benzoate and sodium phenylacetate to bind up glycine and glutamine

65
Q

To Tx defects in the urea cycle enzymes you can replace the missing intermediate with ______ or_______

A

arginine or citrulline

66
Q

in the kidneys and more acidic condition _____ breakdown of glutamine and a less acidic condition ____ the breakdown

A

increase, decrease

67
Q

Kidneys and intestines jointly produce _______

A

arginine

68
Q

Massive resection of the small intestine can cause patients to become ______ deficient

A

arginine

69
Q

intestinal CPS1 and OTC form ______ which is exported into the blood and taken up by the kidneys to for arginine

A

citrulline

70
Q

____________ is the major process for removing nitrogen from amino acids

A

transaminase rxn

71
Q

deamination or serine, glutamate dehydrogenase reactions, bacteria in the instestinallumen, and glutaminase reactions are all sources of_____

A

ammonium (NH4+)

72
Q

what are the 4 main products of nitrogen metabolism?

A

urea, ammonia, creatinine, and uric aicd

73
Q

______ is the mechanism for continuously supplying tissues that use glucose as primary energy source during fasting, exercise etc.

A

the alanine cycle

74
Q

in the alanine cycle the generation of amino nitrogen requires how many ATP’s for the disposal as urea?

A

4

Biochemistry (7 decks)

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