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USMLE Step 1 > Biochemistry-Molecular/Genetics > Flashcards

Biochemistry-Molecular/Genetics Flashcards

1
Q

What is rate limiting step of de novo purine nucleotide synthesis?

A

glutamine PRPP (5-phosphoribosyl-1-pyrophosphate) amidotransferase; inhibited by downstream products: IMP, GMP, AMP; cofactors: THF, glutamine, glycine, aspartate

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2
Q

Lesch-Nyhan Syndrome

A

HGPRT (converts hypoxanthine to IMP and guanine to GMP); tx w/ allopurinol (inhibits xanthine oxidase); X linked recessive

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3
Q

Severe combined T and B immunodeficiency

A

Adenosine deaminase deficiency; causes excess ATP/dATP and inhibits ribonucleotide reductase creating imbalance in nucleotide pool; autosomal recessive

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4
Q

Hereditary orotic aciduria

A

orotate phosphoribosyl transferase and/or OMP decarboxylase deficiency

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5
Q

Amino acids required for purine synthesis

A

glycine, aspartate, glutamate (used by glutamine PRPP amidotransferase)

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6
Q

converts ribonucleotides to deoxyribonucleotides

A

ribonucleotide reductase (inhibited by dATP, feedback)

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7
Q

inhibits dihydroorotate dehydrogenase

A

leflunomide

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8
Q

inhibit IMP dehydrogenase

A

mycophenolate, ribavirin

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9
Q

inhibits ribonucleotide reductase

A

hydroxyurea

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10
Q

inhibits de novo purine synthesis

A

6-MP and azathioprine (6MP prodrug)

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11
Q

thymidylate synthase

A

5-FU

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12
Q

inhibits dihydrofolate reductase in humans, bacteria, or protozoa

A

methotrexate (humans), trimethoprim (bacteria), pyrimethamine (protozoa)

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13
Q

DNA polymerase III

A

5’-3’ DNA synthesis; 3’-5’ exonuclease activity

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14
Q

DNA polymerase I

A

5’-3’ exonuclease activity, excises RNA primer (put down by primase)

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15
Q

endonuclease

A

nucleotide excision repair, base excision repair (glycosylase-AP site)

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16
Q

defective nucleotide excision repair

A

xeroderma pigmentosum–UV induced pryimidine dimers

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17
Q

defective mismatch repair

A

HNPCC

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18
Q

defective NHEJ

A

ataxia telengectasia

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19
Q

drugs that block DNA replication often have what modification?

A

3’-OH group to prevent addition of next nucleotide (DNA/RNA is synthesized 5’-3’

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20
Q

mRNA start codon

A

AUG (rarely GUG)

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21
Q

mRNA stop codons

A

UGA, UAA, UAG

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22
Q

inhibits RNA polymerase II

A

alpha-amantin (from death cap mushrooms); causes severe hepatotoxicity

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23
Q

cytoplasmic P bodies

A

mRNA quality control, contains exonucleases, decapping enzymes, microRNAs

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24
Q

anti smith antibodies

A

antibodies to spliceosomal snRNPs (highly specific for SLE)

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25
Q

anti U1 RNP

A

antibody to snRNP70–highly associated with mixed connective tissue disease

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26
Q

which end of tRNA carries amino acid? what sequence?

A

ALL tRNAs have a CCA on 3’ end that carries AAs

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27
Q

T-ARM of tRNA

A

contains thymidine/pseudourine/cytosine sequence necessary for tRNA ribosomal binding

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28
Q

D-ARM of tRNA

A

contains dihydrouracil residues necessary for tRNA recognition by the correct aminoacle-tRNA synthetase

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29
Q

Anticodon loop of tRNA

A

binds mRNA and is opposite the ACC/amino acid end

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30
Q

charging tRNA

A

aminoacyl-tRNA synthetase, requires ATP, 1 per amino acid matchmaker; requires D-arm of ATP for correct binding

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31
Q

tRNA translocation/activation

A

requires GTP/ATP respectively

32
Q

course facial features, clouded corneas, restricted joint movement, high plasma levels of lysosomal enzymes

A

I-cell disease: inherited lysosomal storage disorder, defect in phosphotransferase, failure of golgi to phosphorylate mannose residues–>proteins delivered extracellularly instead of to lysosomes

33
Q

What specifics does the Golgi modify?

A

modifies N-oligosaccharides on asparagine, adds O-oligosaccharides on serine/threonine, adds mannose-6-phosphate to proteins for lysosomal trafficking

34
Q

traffics protein from ribosome to RER

A

signal recognition particle (SRP); ribonucleoprotein; when deficient–>proteins accumulate in cytosol

35
Q

retrograde trafficking

A

COP1

36
Q

anterograde trafficking

A

COP2

37
Q

trans-golgi trafficking

A

clathrin

38
Q

vimentin

A

connective tissue

39
Q

desmin

A

muscle

40
Q

cytokeratin

A

epithelial cells

41
Q

GFAP

A

neuroglial cells

42
Q

neurofilaments

A

neurons

43
Q

Type 1 Collagen; disease?

A

Bone, skin, tendon, dentin, fascia, cornea, late wound repair; osteogenesis imperfecta type I

44
Q

Type 2 collagen

A

cartilage (including hyaline); vitreous body, nucleus puplosus

45
Q

Type 3 collagen, disease?

A

reticulin–skin, blood vessels, uterus, fetal tissue, granulation tissue–Ehler Danlos vascular type

46
Q

Type 4 collagen; diseases?

A

basement membrane, basal lamina, lens; alport syndrome, goodpasture syndrome

47
Q

which step of collagen synthesis is defective in osteogenesis imperfect?

A

Glycosylation step; formation of procollagen via hydrogen and disulfide bonds to form triple helix of procollagen

48
Q

which step of collagen synthesis is defective in Ehler Danlos?

A

Cross linking step; Cu2+ containing lysyl oxidase; final step to make collagen fibrils

49
Q

multiple fractures with minimal trauma occurring during birth process

A

Osteogenesis imperfecta–autosomal dominant with decreased production of otherwise normal type I collagen; blue sclerae, hearing loss, dental imperfections

50
Q

brittle/kinky hair, growth retardation, low muscle tone as child

A

Menkes disease–impaired copper absorption and transport–decreased activity of lysyl oxidase; problems crosslinking

51
Q

hyperphagia, obesity, intellectual disability, hypogonadism, hypotonia

A

Prader Willi syndrome; maternal imprinting (paternal gene is deleted); chromosome 15

52
Q

inappropriate laughter, seizures, ataxia, severe intellectual disability

A

Angelman Syndrome; paternal imprinting (materal gene deleted); chromosome 15

53
Q

Example of x-linked dominant disorder

A

hypophosphatemic rickets (increased phosphate wasting at PCT)

54
Q

myopathy, lactic acidosis and CNS disease

A

mitochondrial myopathy; failure in oxidative phosphorylation; muscle biopsy shows ragged red fibers; mitochondrial inheritance

55
Q

ADPKD

A

autsomal dominant; PKD1 (chromosome 16); PKD2 (chromosome 4)

56
Q

FAP

A

autosomal dominant; APC (chromosome 5; polyp has 5 letters)

57
Q

telangectasia, recurrent nosebleeds, skin discoloration, AVMs, gi bleeding, hematuria

A

Hereditary hemorrhagic telangectasia, autosomal dominant, aka Osler Weber Rendu syndrome

58
Q

Huntington disease

A

AD; chromosome 4; CAG repeats

59
Q

cystic medial necrosis of aorta; floppy mitral valve, lens subluxation typically upward and temporally

A

Marfan syndrome–fibrillin 1 defect (sheath for elastin)

60
Q

MEN syndromes inheritance pattern

A

autosomal dominant

61
Q

cafe au lait spots and cutaneous neurofibromas

A

NF1, AD, chromosome 17

62
Q

bilateral acoustic schwannomas, juvenile cataacts, meningiomas, ependymomas

A

NF2, AD, chromosome 22

63
Q

numerous benign hamartomas

A

tuberous sclerosis–AD, incomplete penetrance, variable expression

64
Q

retinal, medullary, cerebellar angiomas, bilateral renal cell carcinoma

A

von hippel lindau disease; AD, chromosome 3

65
Q

cystic fibrosis

A

CFTR gene on chromosome 7; AR

66
Q

Some autosomal recessive diseases:

A

albinism, ARPKD, CF, glycogen storage diseases, hemochromatosis and Wilsons, Kartagener, mucopolysaccharidoses (except Hunter syndrome X linked R); PKU, sickle cell, sphingolipidoses (except Fabry XLR w/ incomplete penetrance), thalassemias

67
Q

X-linked Recessive disorders

A

Be Wise Fools GOLD Heeds Silly HOpe: bruton, wiskott-aldrich, fabry, G6PD, ocular albinism, Lesch Nyhan, Duchenne (and becker), hemophilia A/B, Hunter syndrome, OTC deficiency

68
Q

myotonia, muscle wasting, frontal balding, cataracts, testicular atrophy, arrhythmia

A

Myotonic type 1 dystrophy–CTG repeats in CMPK gene

69
Q

post-pubertal macroorchidism, long face with large jaw, large everted ears, autism, mitral valve prolapse

A

Fragile X syndrome–X-linked CGG repeats in FMR1 gene

70
Q

What are the trinucleotide repeats in common repeat disorders:

A

X-Girlfriends First Aid Helped Ace My Test: Fragile X–CGG; Friedrich’s ataxia–GAA; Huntington–CAG; Myotonic dystrophy–CTG

71
Q

Imaging and lab findings in Down Syndrome

A

First trimester US: increased nuchal translucency, hypoplastic nasal bone; serum PAPP-A is decreased, free bHCG is elevated; Quad screen: decreased AFP and estriol; increased bHCG and inhibinA

72
Q

Lab findings in Edwards syndrome

A

everything is down

73
Q

US and Lab findings in Patau syndrome

A

everything is down, but increased nuchal translucency

74
Q

microcephaly, moderate to severe intellectual disability, crying/mewing, epicanthal folds, cardiac abnormalities (VSD)

A

Cri du chat–microdeletion of short arm of chromosome 5 46XX/XY, 5p-)

75
Q

elfin facies, intellectual disability, hypercalcemia, conversant, extremely friendly, cardiovascular problems

A

Williams Syndrome–microdeletion of long arm of chromosome 7

76
Q

22qll deletion

A

Cleft palate, abnormal facies, thymic aplasia, cardiac defects, hypocalcemia (parathyroid aplasia)–defects in 3/4th branchial pouch formation–DiGeorge, velocardiofacial syndrome

USMLE Step 1 (36 decks)

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