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Biochemistry Flashcards

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USMLE® Step 1 flashcards
1
Q

What 5 molecules are used to make purines?

A

Aspartate, glutamine, CO2, glycine, and THF

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2
Q

What 4 molecules are used to make pyrimidines?

A

Aspartate, glutamine, CO2, and ATP

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3
Q

In what order are the base, sugar-PRPP (ribose) assembled in:
Pyrimidines
Purines

A 
Pyrimidines = Base + sugar-PRPP
Purines = Sugar-PRPP + base
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4
Q

What is the rate-limiting step in pyrimidine and purine base synthesis?

A

Pyrimidine - CPS2

Purine - PRPP Synthetase

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5
Q

What is the mechanism of:
Hydroxyurea
5FU

A 
Hydroxyurea = inhibits ribonucleotide reductase
5FU = inhibits thymidylate synthase
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6
Q

Megaloblastic anemia that is not corrected with vitB12 and folate supplementation

A

Orotic aciduria

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7
Q

Increased orotic acid in urine + hyperammonemia

Increased orotic acid in urine without hyperammonemia

A

Ornithine transcarbamylase deficiency

Orotic aciduria

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8
Q

Treatment for orotic aciduria

A

Uridine supplementation (bypass UMP synthase)

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9
Q

What is the mechanism of mycophenylate?

A

Inhibits IMP DH

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10
Q

What is the inheritance pattern of Lesch-Nyhan syndrome?

A

X-linked recessive

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11
Q

What DNA polymerases are used in prokaryotes and what are their functions?

A 
DNApol1 = replaces primers
DNApol3 = leading and lagging strand
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12
Q

What DNA polymerases are used in eukaryotes and what are their functions?

A

a - lAgging strand (has it’s own primase)
B - Mismatch DNA repair
d - leaDing strand
gamma - mitochondrial DNA replication

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13
Q

When is mismatch repair needed?

What disease results from a defect?

A 
Wrong nucleotide is incorporated during replication
Lynch syndrome (hereditary non-polyposis colorectal cancer HNPCC)
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14
Q

When is nucleotide excision repair needed?

What disease results from a defect?

A

When DNA is damaged outside of replication and causes bulky kinks (UV radiation causes thymidine dimers)
Xeroderma pigmentosum

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15
Q

When is base excision repair needed?

What type of DNApol is used?

A

When DNA is damaged outside of replication where the composition of the base is change but the backbone remains intact (non-bulky damage)
DNApol B

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16
Q

What are the steps of:
Nucleotide excision repair
Base excision repair

A 
NER = endonuclease - DNApol - ligase
BER = glycosylase (removes base from the backbone) - endonuclease - DNApol - ligase
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17
Q

When is non homologous end joining repair needed?

What disease results from a defect?

A

dander breaks

Ataxia-telangectasia

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18
Q

What is Bloom syndrome?

How does it present?

A 
Defect in DNA helicase
Sunlight hypersensitivity (similar to XP)
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19
Q

IgA deficiency + poor smooth pursuit/ataxia + spider angiomas + elevated AFP

A

Ataxia-telangectasia

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20
Q

What RNA polymerases are used in eukaryotes and what are their functions?

A

RNApol 1 = rRNA
RNApol 2 = mRNA
RNA pol 3 = tRNA

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21
Q

How is the a-amanitin toxin from the Amanita phalloides mushroom toxic?

A

Inhibits RNApol2 which impairs mRNA synthesis

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22
Q

I cell disease

A

Phosphotransferase mutation - cannot put mannose-6 phosphate on lysosomal enzymes to direct them, so they are released into the interstitial by default

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23
Q

Prader-WIlli syndrome

A

Maternal gene normally silenced, but paternal gene is also deleted - over eating, intellectual disability, hypogonadism, short stature
“POP” - praderwilli, over eating, paternal deletion

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24
Q

Angelman syndrome

A

Paternal gene normally silenced, but maternal gene is also deleted - inappropriate laughter (happy puppet), ataxia, seizures, intellectual disability
“MAMA” - maternal deletion, angelman, mood (laughter), ataxia

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25
Q

How do epinephrine (muscles) and glucagon (liver) raise blood sugar?

A

Bind GCPR (Gs type) - increase intracellular cAMP - activate protein kinase A - activate phosphorylase kinase:

  1. Inhibits glycogen synthase
  2. Activates glycogen phosphorylase
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26
Q

Hypoglycemia/hyperlipidemia + gout + elevated lactic acid + hepatosplenomegaly + enlarged kidneys

A 
VonGierke disease (type 1) = glucose-6-phosphatase mutation
Muscle doesn't release glucose into the blood, so this only affects liver (glycogenolysis and gluconeogenesis)
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27
Q

Hypoglycemia with normal lactic acid and uric acid + normal kidneys + hepatosplenomegaly + muscle weakness

A

Cori disease (type 3) = a-1,6-glucosidase mutation

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28
Q

Muscle cramps and myoglobinuria with strenuous exercise

A

McArdle disease (type 5) = glycogen phosphorylase

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29
Q

Where does glycogen accumulate in Pompe disease?

What organs are affected by infantile and adult type Pompe?

A

Lysosomes
Infant - cardiomyopathy
Adult - respiratory failure

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30
Q

What are the required co-factors for pyruvate DH?

A

B1 (thiamine), B2 (FAD), B3 (NAD), B5 (CoA), and lipoic acid

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31
Q

What 2 metabolites are elevated in pyruvate DH deficiency?

A

Lactic acid (lactic acid DH, pyruvate to lactic acid) and alanine (ALT, pyruvate to Ala)

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32
Q

What is the inheritance pattern for pyruvate DH deficiency?

How is it acquired?

A 
X-linked
Arsenic exposure (depletes lipoid acid and thiamine)
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33
Q

Treatment for pyruvate DH deficiency

A

Purely ketogenic protein and fat diet - Lysine and Leucine

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34
Q 
What part of the electron transport chain is inhibited by:
Rotenone (fish poison), MPTP/MPP
Antimycin A (fish poison)
CN, azide (N3-), CO, H2S
Oligomycin (macrolide)
A

Complex 1
Complex 3
Complex 4
ATP synthase

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35
Q

What enzymes require Selenium?

A

Glutathione peroxidase and reductase

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36
Q

What enzyme is deficient in essential fructosuria?

A

Fructokinase

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37
Q

Hypoglycemia + hepatomegaly/jaundice

A

Fructose intolerance (fructose is trapped in the cells by phosphorylation, but cannot be utilized. Depleted PO4 shuts down gluconeogenesis and cannot correct hypoglycemia)

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38
Q

What enzyme is deficient in fructose intolerance?

What sugars must be avoided?

A

Aldolase B

Fructose or sucrose

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39
Q

Infantile cataracts and elevated galactose in urine/blood

A

Galactokinase deficiency - galactitol accumulates in the lens causing cataracts

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40
Q

Infantile cataracts + hepatomegaly/jaundice + intellectual disability

A

Classic galactosemia

41
Q

What enzyme is deficient in classic galactosemia?

What sugars must be avoided?

A

Galactose-1-phosphate uridyltransferase

Galactose and lactose

42
Q

How long is glycogenolysis used for fuel following a meal?

A

Only 2 hrs

43
Q

What is used as fuel in starvation?

A

Glucose (hepatic gluconeogenesis) and FAs - 24 hrs

Ketone bodies - 48 hrs

44
Q

What does the brain use as fuel in starvation? Muscles?

A

Brain - glucose then ketone bodies

Muscles - FAs

45
Q

Intellectual disability + fair skin + eczema + seizures + musty body odor

A

Phenylketonuria - Phe hydroxylase or tetrahydobriopterin deficiency

46
Q

Dark brown sclera + joint pain + urine turns black when exposed to air

A

Alkaptonuria = Homogentisate oxidase deficiency, homogentisic acid accumulation (toxic to cartilage)

47
Q

Tall/kyphosis + intellectual disability + osteoporosis + downward lens subluxation + thrombosis

A

Homocysteinuria

Homocysteine accumulation damages endothelial cells, predisposing to thrombosis

48
Q

What are 2 causes for homocysteinuria?

A

Cystathionine synthase dysfunction - deficiency or low affinity for vitB6
Homocysteine methyltransferase deficiency

49
Q

Megaloblastic anemia + neurologic dysfunction (spinal cord demyelination) + normal methylmalonyl CoA

A

Homocysteinuria - homocysteine methyltransferase deficiency

50
Q

Hexagonal cystine kidney stones

A

Cystinuria

51
Q

What causes Cysteinuria?

How is it treated?

A

Defective transporter for Cys, Ornithine, Lys, and Arg (COLA) in renal proximal tubule and intestines
Acetazolamide - alkalinizes the urine = basic AAs lose their protons and become charged = increased solubility in the filtrate

52
Q

Neutral aminoaciduria + pellagra

A

Hartnup disease

53
Q

What is the most immediate source of nitrogen for the urea cycle?

A

Aspartate

54
Q

What infection may require vitamin A supplementation?

A

Measles - prevents exfoliative rash

55
Q

Hemolytic anemia + ataxia/peripheral neuropathy + proximal muscle weakness with a poor diet

A

Vitamin E deficiency

56
Q

What 2 vitamins must be given to exclusively breast-fed babies?

A

Vitamin C and D

57
Q

Scaly skin + hepatomegaly + joint pain + headaches

A

Vitamin A toxicity (causes pseudotumor cerebri = headaches)

58
Q

What non-collagen enzyme requires vitamin C?

A

Dopamine B-hydroxylase (DA to NE)

59
Q

What vitamin facilitates Fe absorption?

A

Vitamin C (keeps Fe in the reduced 2+ state)

60
Q

Confusion + opthalmoplegia + ataxia + memory loss

A

Wernicke-korsakoff syndrome (thiamine deficiency)

61
Q

What 2 other conditions are caused by thiamine deficiency?

A

Wet Beriberi - high output heart failure

Dry Beriberi - polyneuropathy

62
Q

Angular chelitis + gossitis

A 
Vit B2 (flavin) or B6 (PLP) deficiency
vitB6 def will also have convulsions (required to make GABA)
63
Q

What are 3 causes of pellagra (vitB3 niacin deficiency)?

A

Hartnup disease, carcinoid syndrome, and isoniazid

64
Q

Indication for niacin therapy

A

Low HDL

65
Q

What vitamin deficiency can lead to adrenal insufficiency?

A

Vitamin B6 (pantothenate, CoA - acetylCoA used to make cholesterol)

66
Q

Which vitamin is a cofactor for the aminotransferases?

A

Vitamin B6 (pyridoxine, PLP)

67
Q

What two vitamins are depleted by isoniazid?

A

Vitamin B3 (niacin) and B6 (PLP)

68
Q

What 4 medications can cause folate deficiency?

A

Phenytoin, sulfonamides, MTX/TMP

69
Q

What type of reaction converts methylmalonyl-CoA to saucily-CoA requiring vitaminB12?

A

Isomerization reaction (methylmalonyl-CoA mutase)

70
Q

GI bleeding with late metabolic acidosis and GI obstruction (weeks later)

A

Fe poisoning (ROS generation causes the GI damage and scarring causes obstruction)

71
Q

What enzymes require Zn?

A

Carbonic anhydrase and LDH

72
Q

What type of patients should receive Zn supplementation?

A

Delayed wound healing

73
Q

Impaire night vision + infertility + delayed wound healing + anosmia + acrodermatitis enteropathica

A

Zn deficiency

74
Q

Wrist/foot drop + colicky abdominal pain + bright horizontal lines near long-bone metaphyses

A 
Lead poisoning (lead lines = deposition of lead in growing bone)
Also causes anemia and basophilic stippling
75
Q

Treatment for lead poisoning

A

Succimer or EDTA

Severe = succimer + dimercaperol

76
Q

What are 2 causes of acrodynia (peeling skin off the finger tips)?

A

Kawasaki disease and Hg poisoning

77
Q

CNS changes + enlarged kidneys + history of eating large fish like swordfish or shark

A

Hg poisoning

78
Q

What 4 conditions are associated with Down syndrome?

A

Duodenal atresia, endocardial cushion defects, ALL (“we ALL fall DOWN”), and alzheimer’s disease

79
Q

What hematologic pathology is seen in newborns with Down syndrome?

A

Polycythemia

80
Q

What are the 2 most common genetic causes for intellectual disability? What is the most common non-genetic cause?

A

Down syndrome then Fragile X syndrome

Fetal alcohol syndrome

81
Q

What does the Quad screen look like in Down syndrome?

AFP, B-hCG, estriol, and inhibin A

A

AFP low, B-hCG high, estriol low, and inhibit A high

put in alphabetical order then start with down and alternate

82
Q

What 3 congenital conditions will show nuchal translucency on 1st trimester ultrasound?

A

Down syndrome (trisomy 21), Patau syndrome (trisomy 13) and Turner syndrome

83
Q

Micrognathia + clenched hands

Quad screen? (AFP, B-hCG, estriol, and inhibin A)

A

Edwards syndrome - trisomy 18 (Election age is 18 - Edwards)

AFP low, B-hCG low, estriol low, and inhibin A normal

84
Q

Midline fascial defects/micropthalmia + polydactyly

What is used for prenatal detection?

A

Patau syndrome - trisomy 13 (Puberty at age 13 = Patau)

Decreased PAPP-A

85
Q

What does FSH and LH look like in Klinefelters?

A

Abnormal seminiferous tubules = decreased Sertoli cell inhibin production = low FSH
Abnormal Leydig cells = decreased testosterone = low FSH

86
Q

Tall + developmental delay + testicular atrophy

A

Klinefelter syndrome (47XXY)

87
Q

High pitched cry/mewing in newborn

A

Cri-Du-Chat = “cry of the cat” (chr5 short arm deletion)

88
Q

Elfin facies + extreme friendliness + hyperCa + intellectual disabiltiy

A

Williams Syndrome - increased sensitivity to vitD = hyperCa

“WILL ferrel in ELF movie”

89
Q

Advanced paternal age is associated with what condition of the child?
What is the inheritance pattern?

A

Achondroplasia

Autosomal dominant FGFR3 mutation

90
Q

Telangiectasia/AVMs throughout the body

A

Osler-Weber-Rendu (hereditary hemorrhagic telangiectasia)

91
Q

What anemia is autosomal dominant?

A

Hereditary spherocytosis

92
Q

What condition that predisposes to particular cancers is inherited in autosomal dominant pattern?

A

MEN

93
Q

Intellectual disability + macroorchidism + mitral valve prolapse

A

Fragile X syndrome

94
Q

What is the genetic cause of fragile X?

A

Trinucleotide repeat CGG

“Chromosome Girly-Girl = chr X”

95
Q

Ataxia + hammer toes/pes cavus + hypertrophic cardiomyopathy + DM

A

Friedreich ataxia

96
Q

What is the genetic cause of Friedreich ataxia?

A

Trinucleotide repeat GAA

“Gait Astoundingly Ataxic”

97
Q

What antibiotic is used in CF that is not typically used in kids?

A

Fluoroquinolones

98
Q

What condition is associated with gargoylism?

A

Hurler syndrome

99
Q

What disorders are X-linked recessive?

“Oblivious Female Will Give Her Boys Her x-Linked Disorders”

A

Ocular albinism, Fabry disease, Wiscott-aldrich, G6PD deficiency, Hunter syndrome, Bruton agammaglobulinemia, Hemophilia A and B, Lesch-nyhan syndrome, and DMD

USMLE (12 decks)

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