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Biochem review USMLE > amino acid metabolism > Flashcards

amino acid metabolism Flashcards

1
Q

essential amino acids

A 
Phenylalanine
Valine
Threonine
Tryptophan
Isoleucine
Methionine
Histidine
Leucine
lysine
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2
Q

mnemonic for essential amino acids

A

PVT TIM HaLL

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3
Q

fate of excess nitrogen from amino acid catabolism

A

converted to urea that is then excreted by the kidneys

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4
Q

rate limiting enzyme in urea cycle

A

CPS I

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5
Q

2 enzymes in the urea cycle that work inside the mitochondria

A

CPS I

ornithine transcarbamoylase

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6
Q

site of urea cycle

A

liver

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7
Q

in what molecule is NH3 transported in the blood?

A

alanine

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8
Q

what occurs in muscle cells to produce alanine? (2 steps)

A

NH3+ a-ketoglutarate = glutamate(NH3)

glutamate(NH3)+pyruvate = alanine (NH3) (by ALT)

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9
Q

what happens to alanine after it reaches the liver?

A

alanine (NH3) + a-ketoglutarate = glutamate (NH3) –> enters urea cycle

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10
Q

acquired cause of hyperammonemia

genetic cause of hyperammonemia

A

genetic- urea cycle enzyme deficiencies

acquired- liver disease

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11
Q

why is hyper ammonia harmful?

A

excess NH4 leads to increased glutamate production (which depletes a-ketoglutarate, thereby stopping the TCA cycle)

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12
Q

treatments of hyperammonemia (4)

A

limit protein in diet
benzoate/phenylbutyrate- bind amino acid/excretion
lactulose- acidifies GI tract to trap NH4+ for excretion
biotin- stimulates OTC

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13
Q

inheritance of ornithine transcarbamoylase deficiency

A

X-linked recessive

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14
Q

consequences of ornithine transcarbamoylase deficiency

A

unable to convert carbamoyl phosphate + ornithine –> citrulline, leads to accumulation of orotic acid

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15
Q

symptoms of ornithine transcarbamoylase deficiency

A

increased orotic acid in blood
decreased BUN
increased ammonia

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16
Q

difference between presentation of ornithine transcarbamoylase deficiency and orotic aciduria

A

ornithine transcarbamoylase deficiency - decreased BUN, increased ammonia
orotic aciduria- no increased in ammonia

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17
Q

tryptophan derivatives (2)

A

Niacin –> NAD+/NADP+ using B6

serotonin –> melanin using BH4

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18
Q

histidine derivative (1)

A

histamine using B6

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19
Q

glycine derivative (1)

A

glycine + succinyl-CoA –> dALA by ALA synthase in heme synthesis (B6 cofactor)

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20
Q

arginine derivatives (3)

A

urea
NO
Creatine

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21
Q

glutamate derivatives (2)

A

GABA (with B6)

glutathione

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22
Q

starting amino acid in catecholamine synthesis

A

phenylalanine

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23
Q

enzyme/cofactor responsible for conversion of phenylalanine –> tyrosine

A

phenylalanine hydroxylase

BH4

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24
Q

enzyme/cofactor responsible for conversion of tyrosine –> dopa

A

tyrosine hydroxylase

BH4

25
enzyme/cofactor responsible for conversion of dopa --> dopamine
dopa decarboxylase | B6
26
inhibitor of dopa decarboxylase
carbidopa (decreases peripheral conversion)
27
what vitamin should be avoided in pts with PD on levodopa?
B6- will increase peripheral conversion of dopa to dopamine = decreased therapeutic benefit and increased SE
28
enzyme/cofactor responsible for conversion of dopamine --> norepinephrine
dopamine b-hydroxylase | vitamin c
29
enzyme/cofactor responsible for conversion of norepinephrine, site
PNMT SAM only in adrenal medulla
30
urine byproduct of dopamine
HVA
31
urine byproduct of NE
VMA
32
urine byproduct of epinephrine
metanephrine, HVA
33
urine byproduct of serotonin
5-HIAA
34
stimulates the conversion of norepinephrine to epinephrine
cortisol
35
2 deficiencies that can lead to phenylketonuria
1) phenylalanine hydroxylase | 2) BH4
36
amino acid that becomes essential in PKU
tyrosine
37
3 substances decreased in PKU
melanin catecholamines thyroxine
38
presentation of PKU (6)
musty body odor, mental retardation, growth retardation, fair skin, eczema, seizures
39
treatment
decrease Phe and increase tyrosine in diet
40
what does screening for PKU detect? when done?
detects presence of phenylketones, done 2-3 days after birth, once effects of maternal phenylalanine hydroxylase has been diminished
41
what is maternal PKU?
occurs when mothers with PKU do not follow appropriate diet during pregnancy, fetus = microcephaly, congenital heart defects, metal/growth retardation
42
cause of alkaptonuria
deficiency of homogentisic acid oxidase (involved in conversion of tyrosine --> fumarate)
43
symptoms of alkaptonuria
accumulation of homogentisic acid leads to black urine, brown pigmentation and arthralgias (homogentisic acid is toxic to cartilage)
44
3 causes of albanism
1) failure of neural crest cell migration 2) tyrosinase def (=decreased melanin synthesis) 3) defective tyrosine transporters
45
risk assoc with albanism
increased skin CA
46
albanism exhibits what inheritance phenomenon
locus heterogenity- different defects on different genes produce the same phenotype
47
what is ocular albanism?
X-linked recessive, only affects eyes
48
2 fates of homocysteine
cystathionine (cystathionine synthase, B6) | methionine (homocysteine methyltransferase, B12)
49
3 causes of homocysteinuria
- cystathionine synthase deficiency - decreased affinity of cystathionine synthase for B6 - homocysteine methyltransferase deficiency
50
symptoms of homocystinuria
increased homocysteine in urine marfanoid- tall, kyphosis, lens subluxation acclerated atherosclerosis (CVA, MI)
51
treatment of cystathionine synthase deficiency
increase cysteine in diet decrease methionine in diet increase B12 in diet
52
treatment of decreased affinity of cystathionine synthase for B6
increase B6
53
cause/effect of cysteinuria
defect in renal tubular amino acid transporter of the PCT= excess excretion of cysteine, ornithine, lysine, arginine
54
symptoms of cysteinuria
cystine stones (hexagonal)
55
treatment of cysteinuria
alkalinization of urine, acetazolamide
56
defect of maple syrup urine disease
decreased a-ketoacid dehydrogenase = block degradation of branched chain amino acids
57
amino acids affected in maple syrup urine disease
isoleucine leucine valine
58
symptoms of maple syrup urine disease
maple syrup odor to urine CNS defects death
59
what is the cause/effect of Hartnup disease?
defective absorption of neutral amino acids int he intestine leads to tryptophan deficiency = decreased Niacin synthesis = pellagra

Biochem review USMLE (11 decks)

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