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USMLE Step 1 > Biochem, Molecular > Flashcards

Biochem, Molecular Flashcards

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USMLE® Step 1 flashcards
1
Q

What vitamin should be supplemented with neonatal phototherapy?

A

riboflavin (B2) bc the light degrades it

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2
Q

Name a genetic disorder that is assoc w abnormal splicing variants.

A

Beta-thalassemia

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3
Q

What are the effects of medium/long-chain acyl-CoA dehydrogenase deficiency? Tx?

A 
Inability to beta-oxidize fatty acids = accumulation of carnitines + less ATP
-hypoketotic hypoglycemia
-hypotonia (frog leg)
-seizures
-hyperammonia
Tx: avoid fasting
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4
Q

Which base pairs indicate splice acceptor site? Splice donor site?

A

acceptor: 3’ invariant AG
donor: 5’ GT/GU

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5
Q

What are the symptoms and treatment for Galastosemia?

A

Absent galatose-1-P UT = cataracts, fail thrive, jaundice

Tx: remove galactose + lactose/glucose from diet

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6
Q

What is primase?

A

Complex that synthesizes a short strand of RNA that’s needed before DNA can be synthesized

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7
Q

What is Beriberi in adults?

A

Profound thiamine def

  • dry = peripheral neuropathy
  • wet = cardiac involvement
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8
Q

What are the symptoms of UMP synthase def?

A

blockage of pyrimidine synthesis –> megaloblastic anemia w orotic crystals in urine

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9
Q

Which 2 enzymes does citrate allosterically affect?

A

negative regulator: phosphofructokinase I (PFK I) (glycolysis)
positive regulator: acetyl CoA carboxylase (fatty acid syn)

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10
Q

What are the risk factors for severe hyperbilirubemia in neonates?

A
  • male
  • premature
  • jaundice within 24hrs
  • maternal use of TMP-SMX (binds albumin which cant bind bili = kernicterus)
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11
Q

How does cortisol stimulate glucose production?

A

Cortisol induces gluconeogenic enzymes by increasing gene expression (not via cascades)

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12
Q

How does delta F508 mutation affect the CFTR gene?

A

Prevents proper folding = unstable and ubiquinated and digested

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13
Q

Lipoprotein lipase catalyzes what process?

A 
Breakdown of triglycerides in chylomicrons into free fatty acids and glycerol
def = accumulation of chylos --> milky plasma
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14
Q

What is Lesch-Nyhan Syndrome and its symps?

A 
HGPRT def = excess purine synthesis (hyperuricemia)
-spastic cerebral palsy
-self-mutilation*(hand/lips)
-gout/arthritis
TX: allopurinol
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15
Q

lead poisoning inhibits which 2 enzymes?

A
  1. aminolevulinate dehydratase (ALA)
  2. ferrochelatase
    = microcytic, hypochromic anemia
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16
Q

What is familial hypocalciuric hypercalcemia (FHH) and its symps?

A

mutation in Ca-sensing receptor gene (CaSR) = no feedback inhibition of PTH –> hyperCa, hypoCa in urine, Hyper/norm PTH

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17
Q

How does phenylalanine affect a fetus (mom w PKU)?

A

Phenylalanine crosses the placenta; if elevated can act as a teratogen to fetus

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18
Q

What is Acute Intermittent Porphyria and its symps?

A 
Porphobilinogen deaminase def = inc urinary delta-ALA and PBG; 5 Ps:
Painful abdomen
ƒ Port wine–colored urine
ƒ Polyneuropathy (tachy, HTN)
ƒ Psychological disturbances
ƒ Precipitated by drugs
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19
Q

What enzyme is mutated in Ehlers-Danlos Syndrome and what does it do?

A

Lysyl hydroxylase; hydroxylation of lysine residues for cross-linking collagen

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20
Q

What is Pompe disease (II)?

A

alpha-1,4-glucosidase def = skeletal and cardiac muscle symps (cardiomegaly, hepatomegaly, heart fail); NO hypoglycemia

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21
Q

What is the molecular mechanism for a trinucleotide repeat expansion mutation?

A

DNA replication error during S-phase; caused by slippage of polymerase during replication of repeat regions

22
Q

What is the biochemical mechanism behind hemorrhagic disease of the newborn?

A

Vit K def –> defective gamma-carboxylation of glutamate residues
-antibiotics can interfere w Vit K production in breast milk

23
Q

What is I-cell Disease?

A

defect in N-acetylglucosaminyl-1-phosphoTRANSFERASE
= golgi fails to phosphorylate mannose –> proteins secreted extracellularly not delivered to lysosomes
-coarse facial features
-immobile joints
-high plasma lyso enzymes
-cell inclusions

24
Q

What is Glucose-6-phosphate Dehydrogenase def?

A

= less NADPH –> RBCs vulnerable to oxidative damage

  • hemolytic anemia w Heinz bodies + Bite cells
  • anemia precipitated by antimalarials, fava beans, sulfas
25
Q

What are the hallmarks of Vit C def?

A

Scurvy: swollen gums, bruising/petechiae, perifollicular hemorrhages, corkscrew hair

26
Q

How are cocaine and PFK-1 related?

A

Cocaine blocks norepi –> tachy + vasoconstrict
= cardiac ischemia and switch to anaerobic metabolism
–> Inc PFK-1 to switch from aerobic to anaerobic

27
Q

What is Maple Syrup Urine Disease?

A

def of branched-chain ketoacid dehydrogenase = no breakdown Iso,Leu,Val

  • lethargy, poor feeding, vomiting
  • CNS: convulsions, coma
  • Mennonites in PA
28
Q

When an obese person diets, where does the majority of glucose come from?

A

glycerol from fat breakdown

29
Q

What is the composition of gallstones from in ppl w hemolytic anemia (sickle cell)?

A

calcium bilirubinate

30
Q

A diet containing milled rice is associated with what vitamin def?

A

Thiamine –> Beriberi (dry:polyneuritis, muscle waste) (wet: cardiomyopathy, edema)

31
Q

Describe a fructose-1-phosphate aldolase (aldolase B) def.

A

= accumulation of fructose-1-phosphate which inhibits glycogenolysis and gluconeogenesis –> severe hypoglycemia when eating fruit

32
Q

Describe a pyruvate carboxylase def.

A

PyrCarb converts Pyruvate –> oxaloacetate; enzyme def = build up of precursors alanine, pyruvate, lactate

  • seizures
  • hypotonia
  • developmental delay
33
Q

Where are chylomicrons produced?

A

enterocytes (intestinal epi cells) using dietary lipids

34
Q

Where are chylomicrons metabolized?

A

vascular endothelium of adipose tissue via lipoprotein lipase

35
Q

Describe Pyruvate kinase def.

A

= dec ATP = rigid RBCs (hemolytic anemia), inc 2,3-BPG

  • hemolytic anemia of newborn
  • mild for adults
  • autosomal recessive (G6PD def is x-linked)
36
Q

What are hallmarks associated with Hereditary Nonpolyposis colon cancer?

A
  • microsatellite instability (dinucleotide)

- loss of function in mismatch repair genes MLH1/MSH2

37
Q

What is Niemann-Pick Disease?

A

Sphingomyelinase def = neurodegen, hepatosplenomegaly, foam cells (fat macros)

Note: No hepato in Tay-Sachs

38
Q

What is ataxia telangiectasia?

A 
defect in ATM gene = no DNA ds break repair
Triad: 
-ataxia (wheelchair)
-angiomas (telangiestasias)
-IgA def
39
Q

NO activates which enzyme to cause vasodilation?

A

Guanylate cyclase

40
Q

Von Gerke (I) is def in what enzyme?

A

glucose-6-phosphate

41
Q

Pompe (II) is def in what enzyme?

A

alpha-1,4-glucosidase
aka
acid maltase

42
Q

Cori (III) is def in what enzyme?

A

debranching enzyme
aka
alpha-1,6-glocosidase

43
Q

McArdle (V) is def in what enzyme?

A

glycogen phosphorylase
aka
myophosphorylase

44
Q

What are the essential amino acids?

A 
PVT TIM HALL
Phen
Val
Tryp
Thre
Iso
Met
His
Arg
Lys
Leu
45
Q

What is homocystinuria?

A

Cystathionine synthase def = marfanoid, kyphosis, lens dislocation, intellect disability

46
Q

What does AATAAA code for?

A

Cleavage and polyadenylation

47
Q

Cancer/tumor antigen to produce the highest antibody titer?

A

HPV 16 E6 (p53) bc its a mutant tumor suppressor, so body attacks w abs

48
Q

What do tyrosine kinases do?

A

act as downstream effectors of various growth factors, they function through phosphorylating tyrosine residues on different proteins

49
Q

What needs to be inhibited in methanol (paint thinner) poisoning?

A

alcohol dehydrogenase bc it forms formaldehyde

50
Q

What does ribosome peptidyl transferase do?

A

Establish covalent bonds between amino acids

51
Q

Impaired voltage-gated Na channels would cause what?

A

slowed conduction (of myelin sheath)

USMLE Step 1 (13 decks)

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