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USMLE > Biochemistry > Flashcards

Biochemistry Flashcards

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USMLE® Step 1 flashcards
1
Q

Neurofibromatosis I

A

AD disorder. Cafe au lait spots, neurofibromas, Lisch nodules (iris hamartomas), skeletal abnormalities. NF1 on chromosome 17.

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2
Q

Pompe’s disease

A

Glycogen storage disease. Deficiency in lysosomal alpha-1,4-glucosidase. Cardiomegaly, weakness, hypotonia. Early death due to cardiorespiratory failure.

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3
Q

Alkaptonuria

A

Congenital deficiency of homogentisic acid oxidase in tyrosine degradation pathway. Homogentisic acid builds up and polymerizes to form alkapton bodies which deposit to cause dark urine and dark cartilage. May have arthralgias and decreased joint mobility.

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4
Q

Angiotensin effect on efferent arteriole of kidney

A

Binds to Gq, activating phospholipase C and cause constriction of the efferent.

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5
Q

Cyanide poisoning

A

Causes HA, confusion, seizures, vomiting, cherry red lips, cyanosis. Binds with high affinity to mitochondrial cytochrome oxidase, inhibiting the electron transport chain.

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6
Q

Maple syrup urine disease

A

Causes hypoglycemia during fasting due to inability to metabolize leucine, isoleucine, and valine.

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7
Q

Neurofibromatosis type II

A

Audosomal dominant mutation on chromosome 22. Acoustic schwannomas, meningiomas, gliomas, neurofibromas, juvenile cataracts.

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8
Q

Homocystinuria

A

Inborn error of methionine metabolism. Diagnosed by elevated homocysteine in blood and urine. AR mutation. Normal at birth. Clinically manifests as failure to thrive and developmental delay. Can present with subluxation of ocular lens. Usually marfanoid habitus with scoliosis, fair complexion, blue eyes, flushing of cheeks. Increased risk of osteoporosis and thromboembolism, May respond to pyridoxine (vitamin B6) which is a cofactor for the deficient enzyme.

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9
Q

Benign fructosuria

A

Deficiency of fructokinase which converts fructose to fructose-1-phosphate. Asympomatic because hexokinase takes over.

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10
Q

Metachromatic leukodystrophy

A

AR disease caused by deficiency of lysosomal arylsulfatase A. Demyelination in central and peripheral nerves. Accumulation of cerebroside sulfate, which appears brown when stained with toluidine blue.

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11
Q

Heterochromatin vs euchromatin

A

Heterochromatin is condensed and transcriptionally inactive. Euchromatin is transcriptionally active.

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12
Q

Histone methylation vs acetylation

A

Methylation represses transcription; histone relaxes coiling and allows for transcription. (Methylation - mute, acetylation - active)

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13
Q

Purines vs pyrimidines

A

Purines: two rings, A and G
Pyrimidines: one ring, C, T, and U

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14
Q

Purine synthesis

A

Sugar + phosphate –> PRPP –> IMP –> AMP and GMP

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15
Q

Pyrimidine synthesis

A

Glutamine + CO2 –> carbamoyl phosphate –> orotic acid –> UMP

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16
Q

Molecular basis of SCID

A

AR adenosine deaminase deficiency. Excess ATP imbalances nucleotide pool –> feedback inhibition of ribonucleotide reductase –> inhibition of DNA synthesis

17
Q

DNA topoisomerase

A

Creates single or double stranded breaks in helix to add or remove supercoils. Drug target of fluoroquinolones.

18
Q

DNA polymerase I

A

Degrades RNA primer and replaces it with DNA. 5’ to 3’ synthesis. 3’ to 5’ and 5’ to 3’ exonuclease activity.

19
Q

Transition vs transversion mutation

A

Transition: purine to purein or pyrimidine to pyrimidine
Transversion: purine to pyrimidine or vice versa

20
Q

Lac operon

A

Activated in e coli when glucose is absent but lactose is available. Low glucose activates activator protein and high lactose unbinds repressor allowing for transcription.

21
Q

When different mechanisms of DNA repair are used

A

Nucleotide excision repair: bulky distoring lesions, G1 phase, defective in xeroderma pigmentosum
Base excision repair: repair of spontaneous/toxic deamination; throughout cell cycle
Mismatch repair: G2 phase, defective in Lynch syndrome (hereditary nonpolyposis colorectal cancer)

22
Q

Nonhomologous end joining

A

Some DNA lost; mutated in ataxia telangiectasia and Fanconi anemia

23
Q

Protein synthesis direction

A

N to C

24
Q

Promotor

A

Site where RNA polymerase II and other TFs bind to DNA in trnascription

25
Q

Eukaryotic RNA polymerases: what they make

A

RNA poly I: rRNA
RNA poly II: mRNA, inhibited by alpha-aminitin in mushrooms
RNA poly III: tRNA
inhibited by actinomycin D
Rifampin inhibits RNA poly in prokaryotes

26
Q

Process of pre-mRNA splicing

A

Primary transcript combines with snRNPs to form spliceosome.
Lariat shaped intermediate formed.
Lariat released to remove intron and join two ends

27
Q

anti-smith antibodies

A

antibodies against the spliceosomal snRNPs. Specific for SLE.

28
Q

Thiamine functions

A

Cofactor for:

  • pyruvate dehydrogenase
  • alpha-ketoglutarate dehydrogenase in TCA cycle
  • transketolase in HMP shunt
29
Q

Thiamine deficiency

A

Triad of opthalmoplegia, ataxia, confusion. Focal hemorrhage and necrosis in mammilart bodies and PAG.

30
Q

Cyanide poisoning

A

Presents with breathing difficulty, palpitations/tachycardia, headache, flushing, N/V, confusion, weakness. Antidote is nitrites.

31
Q

Antibodies present in rheumatoid arthritis

A

Rheumatoid factor: low specificity

Anti-citrullinated peptides (anti-CCP): highly specific

32
Q

Niemann-Pick disease

A

AR disease. Ashkenazi Jeish descent. Deficiency of sphingomyelinase causes sphingomyelin to accumulate in phagocytes. Foamy histiocytes accumulate in liver, spleen, skin. Neurologic degeneration due to sphingomyelin deposition in CNS. Progresses to hypotonia and blindness. May see cherry red spot in eye and hepatosplenomegaly on exam. Death by age 3.

33
Q

Hereditary fructose intolerance

A

Caused by aldolase B deficiency. Present when fructose-containing foods introduced with vomiting, hypoglycemia 20-30mins after eating fructose. Can also present with failure to thrive, jaundice, hepatomegaly

34
Q

Impaired beta-oxidation

A

Causes hypoglycemia after prolonged fasting with inappropriately low ketone bodies. Most commonly due to deficiency of acyl-coA dehydrogenase.

USMLE (17 decks)

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