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MCP > Amino Acid Metab and Urea Cycle > Flashcards

Amino Acid Metab and Urea Cycle Flashcards

1
Q

** concentration of free amino acids** is higher in the cell or out of the cell?

A

intracellular concentration is ocnsiderably higher

this gradient is maintained by active transport of amino acids into cells

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2
Q

the intracellular/extracellular free AA gradient varies with different AA, the greatest with

A

glutamate and glutamine.

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3
Q

** what are the most abundant amino acids in serum.

A

Glutamine and alanine

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4
Q

In the body there is about 100g of free amino acids.

how much is glutamate and glutamine?

how much is essential AA?

A

50% – glutamate, gluatmine

10% – essential AA

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5
Q

*********

What are the essenital AA?

A

“Pvt. Tim Hall”

Phenylalnine
Valine
Trptophan

Threonine
Isoleucine
Methionine

Histidine
Arginine
Leucine
Lysine

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6
Q

____ becomes essential if **methionine is low **

A

Cysteine

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7
Q

_____ becomes essential if phenylalanine is low.

A

tyrosine

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8
Q

essential AA for growth?

A

arginine

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9
Q

inputs into the AA pool are from

A

dietary protein and proteolysis of cellular protein

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10
Q

Approximately half the endogenous protein (6-7kg) is associated with

A

the skeleton and other supporting tissues

(Of which the major protein component is collagen)

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11
Q

Gastrointestinal inputs

70-100g of dietary protein and 35-200g of endogenous protein from sloshed off____ absorbed daily.

A

intestinal cells

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12
Q

Disorders associated with defects in amino acid transport lead to

A

increased levels of these amino acids in the urine,

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13
Q

Disorders associated with defects in amino acid transport

prognosis?

A

these disorders are benign or cause only minor health problems, since amino acids are also absorbed from the intestines as small peptides

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14
Q

___ separate transporters of AA from the gut into intestinal epithelial cells

A

FIVE

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15
Q

transport of amino acids from the gut into intestinal epithelial cell all are ___ symporters

A

NA or PROTON SYMPORTERS

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16
Q

High degree of redundancy with ___ since they overlap considerably in their specifity

A

AA transporters from gut to intestinal epithelial cells

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17
Q

what is the defect involved in Hartnup’s Disease??

A

A defect in the transport system for neutral and aromatic amino acids from the gut and the renal tubules

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18
Q

Hartnup’s Disease sx?

A

4D’s: Diarrhea, Dermatitis, Dementia, Death)

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19
Q

Hartnup’s Disease tx?

A

administration of niacin

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20
Q

how is Hartnup’s Disease dx?

A

diarrhea, dermatitis, dementia, death with HIGH LEVELS OF NEUTRAL OR AROMATIC AA IN URINE

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21
Q

what is the defect in Cysinuria?

A

A defect in the transport system for basic amino acids and cystine (a disulfide- linked dimer of cysteine) from the gut and the renal tubules.

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22
Q

Cystinuria sx?

A

crystals formed by cystine can lead to UTI AND KIDNEY STONES

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23
Q

Cystinuria tx?

A

fluids, and administration of the drug penicillamine (reacts with cystine to form a significantly more soluble compound)


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24
Q

where is trancytosis along the brush border most pronounced?

A

in infants where it enables them to acquire antibodies from breast milk.

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25
Q

Cystic Fibrosis Because of a defect in the chloride channels in the pancreatic secretory ducts, what do these pts need to be given?

A

secretory ducts harden, so need pancreatic enzymes

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26
Q

when is body protein being broken down to free AA?

A

continuously

The rate of this proteolysis varies widely between proteins from half lives of a few minutes to years.

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27
Q

The urinary levels of ____ can provide a measure of muscle protein breakdown.

A

3-methyl histidine

it is liberated when actomyosin is broken down. histidine residues of muscle are methylated posttranslationally

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28
Q

Metabolic breakdown of amino acids to urea and CO2 is a continuous drain. This is reduced during

A

starvation, but is never turned off.

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29
Q

___ and ___ provide complementing essential amino acids.

A

Grains and beans

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30
Q

Normal nitrogen balance (in a healthy person)

A

total daily N intake = totai daily N loss (in urine, skin feces)

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31
Q

If nitrogen losses are less than intake, the subject is in ____ nitrogen balance

A

positive

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32
Q

examples of ppl in positive N balance?

A

children and convalescing adults

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33
Q

If nitrogen losses are more than intake, the subject is in ____ nitrogen balance

A

negative

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34
Q

examples of people in negative N balance?

A

wasting or starvation

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35
Q

Prolonged negative balance can be fatal if loss of body protein reaches about ____of total body protein.

A

one-third

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36
Q

Insufficient quantities of how many essential amino acids is adequate to turn an otherwise nml individual into one with a negative nitrogen balance.

A

just one

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37
Q

In general, ___ proteins are deficient in lysine, methionine, and tryptophan

A

plant

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38
Q

the absence of lysine in low-grade cereal proteins, used as a dietary mainstay in many underdeveloped countries can lead to

A

kwashiorkor syndrome

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39
Q

Free ammonia ion is highly poisonous so the body can move remove free NH + in three ways.

A
  1. Glutamate Dehydrogenase
  2. Glutamine Synthase
  3. Carbamoyl Phosphate Synthase I and II
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40
Q

how Glutamate Dehydrogenase can remove NH4?

A

combine NH4 with a-ketoglutarate —> puts NH4 in glutamate

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41
Q

how Glutamine Synthase removes NH4?

A

NH4 + glutamate —> glutamine

42
Q

how Carbamoyl Phosphate Synthase I and II removes NH4?

A
43
Q

difference between Carbamoyl Phosphate Synthase I and II

A

I. Located in mitochondria for urea cycle
II. Located in the cytoplasm for pyrimidine nucleotide biosynthesis

II does not use NH4

44
Q

what is Transamination?

A

The transfer of an amino group from an AA to an α-keto acid to form a new AA and a new keto acid

45
Q

what is formed with transamination?

A
  1. a new AA
  2. a new keto acid
46
Q

____ an essential cofactor for all transaminations.

A

Pyridoxal phosphate (vitamin b6):

47
Q

_____ functions as a cofactor in a number of reactions including: a) transaminations

b) decarboxylations
c) dehydration of ß-hydroxyamino acids
d) racemizations of α-amino acids e) removal of H2S from cysteine

A

Pyridoxine

48
Q

All ____ appear to have a common enzyme mechanism utilizing pyridoxal phosphate

A

transaminases

49
Q

The α-amino groups of at least 12 amino acids are removed by pyridoxal phosphate transaminase

A

alanine, arginine, asparagine, aspartate, cysteine, isoleucine, leucine, lysine, phenylalanine, tryptophan, tyrosine and valine.

50
Q

____ is an efficient way for cells to send 3 carbon groups back to the liver to be easily converted into glucose while disposing of an NH4 group.

A

alanine, which can be turned into pyruvate

51
Q

Most transaminases converge on the amino acid ___.

A

glutamate

52
Q

why is glutamate one of the most abundant AA inside cells

A

Most transaminases converge on the amino acid glutamate.

53
Q

where does Oxidative Deamination by Glutamate Dehydrogenase?

A

in the mitocondria

54
Q

Glutamate dehydrogenase can use what are a cofactor

A

either oxidized NAD or NADP

55
Q

Under normal conditions in the liver the ratio of NADPH to NADP is ___

A

high

the ratio of NADH to NAD is low,

so that there is always cofactor available to participate in the Oxidative Deamination by Glutamate Dehydrogenase in either the forward or reverse direction.

56
Q

Glutamate dehydrogenase is activated by? inhibited by?

A

activated – adp and gdp

inhibited by – atp and gtp

57
Q

Glutamate is deaminated mainly in the___

A

liver.

58
Q

difference in when liver genederates NADH?

A

If the liver needs energy it will generate NADH for electron transport.

If it is energy rich, it will generate NADPH for biosynthetic reaction.

59
Q

where are Amino acid oxidases found? what are they found to?

A

found in the kidneys and liver

tightly bound to flavins

60
Q

what do Amino acid oxidases convert?

A

an amino acid and a water molecule into its corresponding α-keto acid and ammonia.

61
Q

direct deamination by dehydratases is facilitated in the aa ____ bc of the chemistry of the hydroxyl side

A

serine and threonine,

62
Q

what is The cofactor for both serine and threonine dehydratase is

A

pyridoxal phosphate

63
Q

Homocysteine desulfhydrase is also a pyridoxal phosphate containing enzyme that removes both ___ and ____ from homocysteine.

A

ammonia and sulfur

64
Q

3 alternate mechanisms for AA deamination

A
  1. AA oxidases
  2. Direct deamination by dehydratases
  3. Desulfhydrases
65
Q

how is α-ketobutyrate disposed of?

A
66
Q

what fatty aci dpathway does vit. b12 catalyze?

A

b12 catalyzes the last step of the α-ketobutyrate –> succinyl CoA pathway

67
Q

___release during catabolism of amino acids is toxic and must be constantly removed from the body.

A

Ammonia

68
Q

why does the body converts the free ammonia to urea

A
  • the constant excretion of ammonia in the urine would lead to drastic changes in blood pH
  • urea, a readily soluble and easily excreted compound
69
Q

ammonia and CO2 —>

A

Carbamoylphosphate

70
Q

ammonia and CO2 —> Carbamoylphosphate

Enzyme-

A

carbamoylphosphate synthetase

71
Q

ammonia and CO2 —> Carbamoylphosphate

Energy requirement-

A

Two molecules of ATP

72
Q

carbamoylphosphate and ornithine —> Citrulline

enzyme?

A

ornithine transcarbamoylase (OTC)

73
Q

ornithine transcarbamoylase is an X-linked gene

what rxn is affected with a defect in this pathway

A

carbamoylphosphate and ornithine —> Citrulline

via this enzyme

74
Q

citrulline and aspartate —>

A

Argininosuccinate

75
Q

citrulline and aspartate —> Argininosuccinate

Enzyme-

A

argininosuccinate synthetase.

76
Q

citrulline and aspartate —> Argininosuccinate

Energy requirement?

A

Energy requirement- one molecule of ATP goes to AMP

77
Q

citrulline and aspartate —> Argininosuccinate

what is formed?

A

PPi is generated

it is degraded by pyrophosphatase

78
Q

citrulline and aspartate —> Argininosuccinate

where does asparate come from?

A

transamination of oxaloacetate by glutamate.

79
Q

cleavage of argininosuccinate—>

A

Arginine and Fumarate

80
Q

cleavage of argininosuccinate—> Arginine and Fumarate

Enzyme-

A

Enzyme- argininosuccinate lyase (argininosuccinase)

81
Q

cleavage of arginine.—>

A

Urea and Ornithine

82
Q

cleavage of arginine.—> Urea and Ornithine

Enzyme-

A

arginase

83
Q

Urea acid cycle

____ <——> Urea + 2ADP + 1 AMP + PPi + Fumarate + 2Pi

A

CO + NH + + 3ATP + Aspartate + 2H O

84
Q

CO + NH + + 3ATP + Aspartate + 2H O <——> ____

A

Urea + 2ADP + 1 AMP + PPi + Fumarate + 2Pi

85
Q

what urea cycle enzymes are in the Mitchondria?

A

carbamoylphosphate synthetase
ornithine transcarbamoylase

86
Q

what urea cycle enzymes are in the Cytosol?

A

argininosuccinate synthetase argininosuccinate lyase arginase

87
Q

Urea carries ___ammonia groups

A

two ammnoia

88
Q

Urea Soluble to ___10M (640g/l)

A

>

89
Q

Why Urea? (4)

A
  • Carries two ammonia groups
  • Soluble to >10M (640g/l)
  • Non protonatable-10% solution pH 7.2
  • Low reactivity (inert)
90
Q

KEY STEPS OF THE UREA CYCLE ARE CARRIED OUT IN THE MITOCHONDRIA?

A
  1. NH4+ + CO2 + 2 A TP —> CARBAMOYL PHOSPHA TE
  2. ORNITHINE —> CITRULLINE
91
Q

Protein free diet- urea excretion accounts for only ___% of the total urinary nitrogen as
compared to 80% in a normal diet.

A

60

92
Q

with a ___ diet, levels of urea cycle enzymes decline

A

protein free diet

93
Q

High Protein diet- or in starvation, urea cycle enzymes

A

increase several fold.

since gluconeogenesis from amino acids is high

94
Q

symptom of most of the diseases caused by defective urea cycle enzymes?

A

An accumulation of ammonia in the blood

95
Q

___ deficiency is the most common urea cycle disorder

A

OTC

* due to its presence on the X chromosome

96
Q

Mental Retardation is seen with what urea acid disorder?

A

Citrullinemia

defect in Argininosuccinate Synthetase

97
Q

Argininosuccinic aciduria

defect is in what enzyme?

what is seen in the blood?

A

defect – Argininosuccinase

blood – NH4 and Argininosuccinic Acid

urine – Arginosuccinic Acid

98
Q

Hyper- ammoniemia

defect is in what enzyme?

what is seen in the blood?

A

enzyme – Carbamoyl Phosphate Synthase

blood – High NH4

99
Q

Arginiemia

defect is in what enzyme?

what is seen in the blood?

defect?

A

defect – Arginase

blood – High NH4 and Arginine

urine – Arg, L ys, Orn

100
Q

Hyper- ornithinemia

defect is in what enzyme?

what is seen in the blood?

urine?

A

defect –Ornithine Transcarbamylase

blood – High NH4, orotate and Ornithine

urine – Ornithine

101
Q

Treatment of urea cycle disorders usually includes

A

low protein diet that is supplemented with arginine or citrulline since arginine usually becomes essential in these patients.

administration of sodium benzoate and sodium phenylacetate

102
Q
A

MCP (16 decks)

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