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Basic Biochemistry > 30. Amino acid disorders + Urea cycle > Flashcards

30. Amino acid disorders + Urea cycle Flashcards

1
Q

Phenylketonuria results from

A

dec phenylalanine hydroxylase or

dec tetrahydrobiopterin

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2
Q

tyrosine becomes essential

and phenyalanine accumulates

A

phenylketonuria

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3
Q

tx of phenylketonuria

A

dietary control to dec phenylalanine and

inc tyrosine

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4
Q

congenital deficiency of homogentisate oxidase in the degradative pathway of tyrosine, leading to build up of homogentisic acid

A

alkaptonuria

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5
Q

defective melanin synthesis from tyrosine which may be from
•defective tyrosine transporters
•absence of copper requiring enzyme tyrosinase

A

albinism

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6
Q

defect in methionine degradation

A

homocystinuria

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7
Q
  • high plasma and rinary levels of homocysteine and methionine
  • low levels of cysteine
A

homocystinuria

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8
Q

tx of homocystinuria

A

restriction of methionine

supplementation with vit B6,B12 and folate

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9
Q

methionine synthase co-enzyme

A

methylcobalamin

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10
Q

cystathionine ß-synthase co-enzyme

A

pyridoxal phosphate

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11
Q

Homoysteine –> methionine requires

A

methionine synthase

co-enzyme: methylcobalamin

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12
Q

Homocysteine –> cystathionine

A

cystathionine ß-synthase

coenzyme:pyridoxal phosphate

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13
Q

caised by
•deficiency of cystathione ß–synthase enzyme
•defective methylcobalamin synthesis
•or abnormality in methylene tetrahydrofolate reductase

A

Homocystinuria

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14
Q

inherited defect of the renal tubular amino acid transporter for cystine, ornithine, lysine, arginine in the PCT of kidneys

A

cystinuria -CORK

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15
Q

tx of cystinuria

A

acetazolamide to alkalinize the urine

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16
Q

defect in the conversion of methylmalonyl coa to succinyl coa
•involves metabolism of isoleucine, valine, threonine and methionine

A

methylmalonyl coa mutase deficiency

IVTM

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17
Q

blocked degradation of branched amino acids (Isoleucine, valine and leucine) due to alpha ketoacid dehydrogenase complex

A

maple syrup urine disease

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18
Q

tx of MSUD

A

dietary restriction of valine, isoleucine and leucin to the minimum

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19
Q
  • severe mental retardation
  • fair skin and eczema
  • musty body odor
A

phenylketonuria

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20
Q

black urine on standing

A

alkaptonuria

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21
Q

accumulation of phenylketones
•phenylpyruvate
•phenyllactate
•phenylacetate - characteristic odor to urine

A

phenylketonuria

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22
Q
  • dark connective tissue (ochronosis)

* may have debilitating arthralgias

A

alkaptonuria

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23
Q

absence of pigment from hair, eyes skin

inc risk of skin cancer

A

albinism

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24
Q 
ectopia lentis 
faulty bone development
mental retardation
tendency to form thrombi
MI 
stoke in children and young adults
A

homocystinuria

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25
Q

this amino acid disorder can cause staghorn calculi

A

cystinuria-cystine kidney stones

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26
Q

seizure, encephalopathy,

and stroke at age of 1 month to 1 year

A

methylmalonyl coa mutase deficiency

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27
Q

sweet odor in urine
vomiting
seizures
mental retardation

A

maple syrup urine disease

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28
Q

conversion of the body’s nitrogenous waste to urea

A

urea cycle

29
Q

where does urea cycle occur

A
  • in the liver only

* mitochondria and cytosol of hepatocytes

30
Q

what are the substrates of urea cycle

A
  • NH3 (derived from oxidative deamination of glutamate)
  • aspartate
  • CO2
  • 3 ATP
31
Q

what is the product of urea cycle

A

urea; fumarate; H2O

32
Q

what is rate limiting step of urea cycle

A

NH3 + CO2 –> carbamoyl phosphate
enz: carbamoyl phosphate synthetase I
Allosteric activator: N-acetylglutamate

33
Q

Enzymes of the urea cycle and location of the reaction

A
  1. carbamoyl phosphate synthetase I (mitochondria)
  2. Ornithine transcarbomylase (mitochondria)
  3. arginosuccinate synthetase (cytosol)
  4. arginosuccinate lyase (cytosol)
  5. arginase (cytosol)
34
Q

synthesis of 1 mol of urea requires
___ ATP
___ high energy bonds

A
  • 3 ATP

* 4 high energy bonds

35
Q

urease positive bacteria convert urea to

A

CO2 and NH3

36
Q

Fates of urea

A
  1. urea-> kidney-> excretion in the urine

2. some urea -> intestine -> urease positive bacteria –> CO2 + NH3

37
Q

amount of urea excreted each day by a healthy adult

A

30 g

38
Q

urea accounts for ___% of nitrogenous excretory products

A

90%

39
Q

ammonia travels to the liver mainly in the form of

A

alanine and glutamine

40
Q

provide nitrogen that is used to produce urea

A

NH4+

and aspartate

41
Q

serves as a carrier that is generated by urea cycle

A

ornithine

42
Q

carbamoyl phosphate synthase I is located in this organelle

A

mitochondria

43
Q

carbamoyl phosphate synthase I

activated by

A

N-acetylglutamate

44
Q

location of ornithine transcarbamoylase

A

mitochondria

45
Q

this is transported in the cytosol in exchange for cytoplasmic ornithine

A

citrulline

46
Q

formation of arginosuccinate

A

citrulline + aspartate –> arginosuccinate
ATP -> AMP + iP
enz: arginosuccinate synthetase

47
Q

formation of arginine

A

argininosuccinate –> arginine + fumarate

Enz: argininosuccinate lyase

48
Q

fumarate from reaction 4 of urea cycle can be converted to ___

A

fumarate –> malate –> glucose (fasting state)

fumarate –> oxaloacetate –> oxaloacetate –> (via transamination) aspartate

49
Q

arginine is cleaved for form

A

Arginine –> Urea + Ornithine

Enz. arginase

50
Q

inhibitor of arginase

A

ornithine

51
Q

when the cell requires additional ornithine, it is sythesized from

A

glucose via glutamate

52
Q

arginine can be synthesized from

A

a. first 4 rxns of urea cycle

b. glucose via ornithine

53
Q

Converts ammonium and bicarbonate into carbamoyl phosphate. This is the rate-limiting step in the urea cycle. This reaction requires two ATP and occurs in the mitochondria.

A

Carbamoyl phosphate synthetase I

54
Q

Combines ornithine and carbamoyl phosphate to form citrulline. Located in mitochondria.

A

Ornithine transcarbamoylase

55
Q

Condenses citrulline with aspartate to form arginosuccinate. This reaction occurs in the cytosol and requires one ATP.

A

Argininosuccinate synthetase

56
Q

Splits argininosuccinate into arginine and fumarate. Occurs in the cytosol.

A

Argininosuccinate lyase

57
Q

Cleaves arginine into one molecule of urea and ornithine in the cytosol. The ornithine is then transported back into the mitochondria for entry back into the cycle.

A

Arginase

58
Q

Although the liver normally has a great capacity for urea synthesis, the enzymes of the urea cycle are induced if a high-protein diet is consumed for ______

A

4 days or more

59
Q

Purpose of urea cycle

A

allows for the excretion of NH4+ by transforming ammonia into urea, which is then excreted by the kidneys.

60
Q

occurs when there is a deficiency in one of more of the urea cycle enzymes, causing insufficient removal of NH4+.

A

Hyperammonemia

61
Q

Neurotoxic effects - Hyperammonemia

A 
Tremors
slurring of speech
vomiting 
blurring of vision
cerebral edema
somnolence 
coma 
death
62
Q

most common cause of hereditary hyperammonemia

A

ornithine transcarbomylase deficiency

63
Q

most severe cause of hereditary hyperammonemia

A

carbamoyl phosphate synthase-1 deficiency

64
Q

Hereditary hyperammonemia is characterized by

A

hyperammonemia
elevated glutamine
dec BUN
respiratory alkalosis

65
Q

tx of hereditary hyperammonemia

A
  1. restriction of dietary protein

2. phenylbutyrate –> phenylacetate, which binds to glutamine and is excreted as phenylglutamine

66
Q

Acquired hyperammonemia is seen in

A

adults with compromised liver fx

cirrhosis : portal blood is shunted directly to systemic circulation without passing through the liver

67
Q

purely ketogenic aa

can be converted to form acetyl coa or acetoacetyl coa

A

Lysine , Leucine

KL-keto

68
Q

Glucogenic and ketogenic amino acds

can be converted to form acetyl coa or acetoacetyl coa, pyruvate or intermediates of krebs cycle

A

phenylalanine
tyrosine
Isoleucine
Tryptophan

FYIW -both

Basic Biochemistry (50 decks)

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