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Medical Biochemistry > Exam 4 purines, pyrimidines and porphyrins section: things to know > Flashcards

Exam 4 purines, pyrimidines and porphyrins section: things to know Flashcards

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USMLE® Step 1 flashcards
1
Q

Lesch-Nyhan Syndrom

A

self-mutilating behavior;hyperuricemia; uric acid in urine; low HGPRT activity.

Hyperuricemia caused by decreased purine reutilization.
HGPRT is used to recycle purines

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2
Q

methotrexate

A

folic acid analog; can cause folic acid deficiency; symptoms of weakeness, fatigability, nausea and diarrhea

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3
Q

what do you make from inosine

A

purines, pyrimydines, GMP from XMP

you need inosine to make pyrimidines to make CTP from UTP

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4
Q

what inhibits PRPP in purine synthesis?

A

AMP, IMP, GMP

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5
Q

what inhibits phosphoribosylamine? in purine synth.

A

AMP, IMP, GMP

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6
Q

purine synt: what inhibits IMP dehydrogenase

A

GMP

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7
Q

purine synt: what inhibits adenylosuccinate synthetase?

A

AMP

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8
Q

what activates ribonucleotide reductase? what inhibits it ?

A

ATP; inhibited by dATP

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9
Q

crigler-najjar syndrome, type I

A

jaundice; increased unconjugated bilirubin level in serum, low fecal urobilinogen level; liver biopsy result low activity of enzyme UDP-glucoronyl transferase.

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10
Q

gilbert syndrome

A

jaundice, decreased UDPGT activity. no history of dark colored urine, clay colored stools, abdominal, blood transfusion, illegal drug use. no alcohol compsumption.
high unconjugated bilirubin without other symptoms

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11
Q

porphyria cutanea tarda

A

chronic blistering and scarring of skin when exposed to sunlight; smoker, drinker, worsen his condition. urine and plasma havehigh level of uroporphyrin.
uroporphyrinogen decarboxylase deficiency.

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12
Q

acute intermittent porphyria

A

treat with glucose; intravenous hemin injection to decrease synthesis of hepatic ALAS1.
NOT photosensitive. PBG deaminase defect. PBG and ALA accumulate in urine.
abdominal pain, motor system neuropathies, induced by drugs, alcohol and sun exphsure.

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13
Q

regulation of heme synthesis

A

ALA synthase is rate-limiting. regulated by loevels of heme. inhibit expression of ALAS1, transfer of ALAS1 to mito, catalytic activity of ALAS1.

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14
Q

erythropoeitic protoporphyria

A

deficiency in ferrochetalase

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15
Q

role of ferrochelatase

A

needs ascorbic acid and cysteine. converts protoporphyrin IX into protoheme IX

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16
Q

neonatal jaundice

A

low level lingandin in liver at birth
low hepatic glucuronyl-transferase activity
treat with phototherapy or exchange transfusion
light from fluorescent lamp

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17
Q

Gout

A

pain in big toe, joint pain, alcohol and beef consumption. sodium urate has reduced solubility at lower temperature.

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18
Q

primary renal and primary metabolic gout

A

renal: hyperuricemia caused by underexcretion of uric acid
metabolic: over production of purines and uric acid

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19
Q

committed step in biosynthesis of adenine and guanine nucleoside monophosphates is catalyzed by

A

glutamine-PRPP amidotransferase; inhibited by AMP, GMP and IMP; activated by PRPP

20
Q

allopurinol

A

inhibits xanthine oxidase

21
Q

pyrimidine nucleotide biosynthesis regulated by allosteric binding of UTP to

A

ribose 5 phosphate as a substrate

22
Q

folate deficiency leads to decreased rate of synthesis of

A

amino acids, thymidylate and AMP

23
Q

lead intoxication mechanism

A

inhibition of enzymes in her RBCs that are present in the mito and in the cytosol. affects ALA dehydratase and ferrochelatase

24
Q

in porphyria cutanea tarda, phlebotomy is used form

A

reducing iron stores since can be influenced by hepatic iron overload

25
Q

crigler-Najjar syndrome type II

A

presence of bilirubin monoglucuronide conjugates in urine. UDPGT deficiency is benign. partial deficiency of gene.

26
Q

ALA synthase reaction

A

glycine to delta-aminolevulinate with pyridoxal phosphate

27
Q

bilirubin formation

A

hemoglobin to heme, heme to biliverdin, beliverdin to bilirubin

28
Q

what does biliary obstruction cause?

A

elevated direct/conjugated bilirubin in blood: if blilirubin is conjugated, UDPGT works, so there no deficit, which causes CN I and II and Gilbert syndrom

29
Q

mechanism of methotrexate

A

inhibits dihydrofolate reductase to suppress synthesis of dTMP and purine nucleotides. antiinflammatory used for RA.

30
Q

why is folate important in treating pernicious anemia?

A

tetrahydrofolate derivatives are essential for the synthesis of IMP and dTMP in humans.

31
Q

febuxostat mechanism

A

xanthine oxidase inhibitor

32
Q

colchicine

A

inhibit microtubule formation and prevents phagocytic cells from engulfing urate crystals. used for gout to alleviate inflammation.

33
Q

uricosuric agents

A

promote renal clearance of uric acid by inhibiting a urate-anion exchanges that mediates urate re-absorption.

34
Q

how does 5-flurouracil (5-FU) treatment work?

A

suppresses cell prolieration by inhibiting dTMP (thymidylate) synthesis

35
Q

Adenosine deaminase deficiency

A

causes immune dysfunction due to accumulation of dATP in body, which is a potent inhibitor of ribonucleotide reductase. treat with bone marryow transplant.

36
Q

chronic hepatitis symptoms

A

jaundice, mildly protruberant abdomen, high serum levels of indirect bilirubim. disease impairs bilirubin conjugation and thus increases level of unconjugated bilirubin in blood

37
Q

excess unconjugated bilirubin

A

increased bilirubin formation
defective liver uptake
defective conjugation

38
Q

excess conjugated bilirubin

A

defective transport to bile

bile duct blockage

39
Q

what is secreted along with urobilinogens that are not absorbed

A

stercobilin, orange browned colored pigments

40
Q

ALA dehydratase reaction

A

ALA to PBG; needs zinc; inhibited by lead, can cause anemia and lead poisoning

41
Q

hemolytic anemia

A

anemia, enlarged spleen, jaundice, blood problem; bizarre looking RBCs, pyruvate kinase deficiency.
disease involved excess bilirubin load because can’t metabolize bilirubin or because of hemolytic process.
breakdown of RBCs causes hemolytic jaundice. increased indirect plasma biliruben. increased urobilonogen level in plasma and urine.

42
Q

how does body compensate in pyruvate kinase deficiency?

A

increase 2,3BPG

43
Q

three types of hyperbilirubinemia

A

hemolytic anemia: high un/con bili (bile)
hepatitis: high un/con blood)
biliary duct stone: hih unco blood/high con blood

44
Q

why use phenobarbital to treat Crigler-Najjar syndrome type II?

A

phenobarbital can induce synthesis of hepatic UDP glucuronyl transferase (UDPGT) so that bilirubin conjugation can be stimulated in the patient. won’t work for type I.

45
Q

Dubin Johnson syndrome

A

jaundice no enlarged liver or spleen, no liver failure; abnormally elevated levels of conjugated bilirubin and several liver enzyumes. high coproporphyrin I and III in urine. liver was dark green.
caused by defective transporter for conjugated bilirubin.

46
Q

what causes porphyria cutanea tarda

A

deficiency in urophorpyrinogen decarboxylase. uroporphyrin accumulates in urine and patients are photosensitive.

Medical Biochemistry (3 decks)

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