Nitrogen Metabolism Flashcards

1
Q

first step of nitrogen removal and enzyme involved

A

oxidative deamination via glutamate dehydrogenase

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2
Q

key player in AA metabolism

A

glutamate

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3
Q

source of carbon skeletons for urea cycle generated from transamination reactions

A

aspartate

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4
Q

nitrogen sources for the urea cycle

A

Glu/Gln

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5
Q

inborn errors of AA resorption (2)

A

hartnup - nonpolar AA

Cystinuria - dibasic AA

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6
Q

AA are resorbed in which portion of the nephron

A

proximal convoluted tubule

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7
Q

cystinuria is characterized by defective ________ enzyme in what tissue

A

shared dibasic-cystine transporter in the proximal renal tubule and JEJUNAL MUCOSA

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8
Q

what picks up the slack for the shared dibasic-cystine transporter in the small intestines?

A

a peptide transporter

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9
Q

hartnup is characterized by a defective ________ enzyme in what tissue

A

neutral AA transporter in the proximal renal tubule and jejunal mucosa

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10
Q

most important AA that is ineffectively resorbed in the PCT in patients with hartnup is

A

tryptophan, precursor for neurotransmitters

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11
Q

dibasic AA

A
COAL
Cystine 
Ornithine 
Argnine 
Lysine
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12
Q

neutral AA transporter deficiency

Ala, Ser, Thr, Val, Leu, Ile, Phe, Tyr, Trp, Gln, Asn

A

hartnup disease

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13
Q

Trp is the precursor for what molecules

A

serotonin
melatonin
niacin (which is a precursor for NAD) - note niacin deficiency

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14
Q

manifestations of Hartnup disease

A

failure to thrive, nystagmus, intermittent ataxia, tremor and photosensitivity
pellagra like dermatosis
attacks triggered by sunlight, drugs, physical stress

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15
Q

treatment for hartnup

A

nicotinic acid

niacin repletion and high protein diet, daily nicotinamide supplementation

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16
Q

nitroprusside test indicates

A

cystinuria

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17
Q

cystinuria can dissolve kidney stones by changing their diet to be more

A

alkalinic

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18
Q

phenylketonuria is caused by deficient

A
Phenylalanine hydroxylase (PAH) 
most common IEM
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19
Q

PKU symptoms can be limited by

A

dietary limitation of Phe and supplementation of Tyr

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20
Q

secondary PKU is characterized by

A

Tetrahydrobiopterin deficiency
THB is a key coenzyme in phenylalanine hydroxylase
defect in synthesis/regeneration of B4

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21
Q

PKU babies must be treated before _____ of age
Dietary restrictions begin if blood Phe levels are greater than _____
some patients with milder forms can increase their metabolic control with supplementation with _______

A

2 weeks of age
6mg/dL
improved metabolic control when treated with THB

22
Q

Tetrahydriobiopterin is a cofactor for what enzyme

A

phenylalanine hydroxylase

23
Q

synthetic THB treats what IEM

A

secondary PKU

24
Q

tyrosinemias are characterized by

A

elevated blood levels of tyrosine

25
deficient fumarylacetoacetate hydrolase results in what form of tyrosinemia and what does the enzyme do
Type I | converts tyrosime to fumarate
26
type I tyrosinemia is characterized by deficient
fumarylacetoacetate hydrolase
27
Type I tyrosinemia babies have a _____ like smell and excrete ______, which is toxic to liver and kidneys, interferes with the TCA cycle, causes renal tubule dysfunction and inhibits biosynthesis of heme
cabbage | secrete succinylacetone
28
type II tyrosinemia is characterized by
defective tyrosine aminotransferase | results in photophobia/skin lesions
29
type III tyrosinemia is characterized by
defective p-hydroxyphenylpyruvate oxidase and results in intermittent ataxia
30
what type of tyrosinemia is most common and used to require a liver transplant?
type I deficient fumarylacetoacetate hydrolase buildup of succinylacetone
31
defective homogentisate oxidase, an enzyme in tyrosine degradation pathway, results in black urine and bones is termed
alkaptonuria
32
a buildup of homogentistic acid is due to what enzyme in alkaptonuria
homogentisate oxidase
33
NH3 toxicity MoA
permeates membranes | pH imbalance, swelling of astrocytes in the brain --> cerebral edema/intracranial hypertension
34
enzyme that catalyzes the oxidative deamination of glutamate to alpha-ketoglutarate
glutamate dehydrogenase
35
ammonia depletes what NT
glutamate
36
gout is a buildup of
uric acid in the blood and deposition of sodium urate crystals primary hyperuricemia --> overproduction of uric acid Secondary hyperuricemia --> underexcretion of uric acid
37
diets rich in ________ along with what other foods/drinks trigger gout
purines | alcohol, meat, seafood
38
treatments of gout
colchicine decreases the movement of granulocytes to the affected areas use of allopurinol inhibits xanthine oxidase
39
hyperammonemia is caused by defects in what enzymes
six enzymes of the urea cycle or 3 specific transporters | mitochondrial ornithine carriers, mitochondrial Asp/Glu carrier, dibasic AA transporter
40
more severe cases of hyperammonemia are due to defects in what enzymes
3 specific transporters | mitochondrial ornithine carriers, mitochondrial Asp/Glu carrier, dibasic AA transporter
41
ornithine transcarbamoylase deficiency results in what condition
hyperammonemia defects cause excess carbamoyl phosphate which can spill out into cytoplasm metabolized by pyrimidine synthesis pathway to orotic acid then accumulates/excreted in the urine (orotic aciduria) --> decreases BUN
42
first step of de novo pyrimidine synthesis is mediated by what enzyme
carbamoyl phosphate synthetase II - cytosol | unique from mitochondrial isoform
43
carbamoyl phosphate synthetase I
urea cycle mitochondrial NAG activated
44
Carbomyl phosphate synthetase II
pyrimidine synthesis cytosolic PRPP activated
45
Carbamoyl phosphate synthetase I is the rate limiting step for what process
urea cycle deficiency == hyperammonemia creates carbamoyl phosphate which is used added to ornithine to make citrulline (allows urea to exit the mitochondria)
46
bilirubin is conjugated with
glucuronic acid | by UDP glucuronyl transferase
47
unconjugated bilirubin is trasnported to the liver from the spleen using
albumin?
48
heme is broken down to bilirubin in the
macrophage
49
unconjugated bilirubin is water ______ while conjugated bilirubin is water _______
insoluble | soluble
50
jaundice is common in newborns because
placenta handles removal of bilirubin, after birth babies liver must take over the job