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USMLE Step 1 > FA Biochemistry > Flashcards

FA Biochemistry Flashcards

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USMLE® Step 1 flashcards
1
Q

Orotic Aciduria

A
  • inability to convert orotic acid to UMP
  • increased orotic acid in urine; megaloblastic anemia (does not improve with B12 or folate); failure to thrive
    Treatment: oral uridine administration
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2
Q

Leflunomide

A

Inhibits dihydroorotate dehydrogenase

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3
Q

Hydroxyurea

A

Inhibits ribonucleotide reductase

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4
Q

Mycophenolate and Ribavirin

A

inhibit IMP hydrogenase

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5
Q

6-Mercaptopurine (6-MP)

A

inhibits de novo purine synthesis

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6
Q

5-fluorouracil

A

inhibits thymidylate synthase (decrease deoxythymidine monophosphate)

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7
Q

Methotrexate

A

inhibits dihydrofolate reductase in humans

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8
Q

Trimethoprim

A

inhibits dihydrofolate reductase in bacteria

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9
Q

Pyrimethamine

A

inhibits dihydrofolate reductase in protozoa

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10
Q

Adenosine deaminase deficiency

A

excess ATP and dATP imbalances nucleotide pool via feedback inhibition of ribonucleotide reductase –> prevents DNA synthesis
– dec lymphocyte could (major cause of autosomal recessive SCID)

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11
Q

Fluoroquinolones

A

inhibit DNA gyrase (prokaryotic topoisomerase II)

– prevents bacterial division

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12
Q

Transition Mutation

A

purine to purine

pyrimidine to pyrimidine

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13
Q

Transversion Mutation

A

purine to pyrimidine

pyrimidine to purine

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14
Q

Missense Mutation (+ example)

A

Nucleotide substitution resulting in changed amino acid.

Sickle cell disease

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15
Q

Nonsense Mutation

A

Results in early stop codon

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16
Q

Frameshift Mutation (+ example)

A

deletion or insertion of a number of nucleotides not divisible by 3 –> msireading of all nucleotides downstream
– usually results in non-functional protein
– throws off “commaless sequence”
Duchenne muscular dystrophy (deleted dystrophin): X Linked

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17
Q

Mismatch Repair Disease

A 
Lynch Syndrome (hereditary nonpolyposis colorectal cancer: HNPCC)
- Autosomal Dominant
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18
Q

Nucleotide Excision Repair Disease

A

Xeroderma Pigmentosum: prevents repair of pyrimidine dimers from UV light exposure

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19
Q

Nonhomologous End Joining Disease

A

Mutated in ataxia telangiectasia:
- defects in ATM gene; breaks result in cell cycle arrest
Triad: cerebellar defects (Ataxia), spider Angiomas, and IgA deficiency

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20
Q

Antibodies to spliceosome snRNPs

A

anti-Smith antibodies

highly specific for SLE

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21
Q

anti-U1 RNP antibodies

A

highly associated with mixed connective tissue disorder

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22
Q

Enzyme for Charging tRNA

A

Aminoacyl-tRNA synthetase
– attaches amino acid to CCA 3’ end of the rRNA
(CCA: Can Carry Amino acids)

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23
Q

Cells rich in rER

A

Mucus-secreting goblet cells of the small intestine
Antibody-secreting plasma cells
— synthesis of secretory proteins

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24
Q

Cells rich in sER

A

Liver hepatocytes
Steroid Hormone-Producing cells of the Adrenal Cortex and Gonads
– sites of steroid synthesis and detoxification of drugs and poisons

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25
Q

Peroxisome

A

catabolism of very-long-chain fatty acids, branched-chain fatty acids, and amino acids
(beta: oxidation: long-chain fatty acid degradation occurs in mitochondria)

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26
Q

I-cell disease

A

inclusion cell disease: inherited lysosomal storage disorder
- defect in phosphotransferase: failure of the Golgi to phosphorylate mannose residues (dec mannose-6-phosphate) on glycoproteins –> proteins secreted extracellularly rather than delivered to lysosomes

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27
Q

Proteasome (+ disease implication)

A

degrades damaged or ubiquitin-tagged proteins

- defects in the ubiquitin-proteasome system have been implicated in some cases of Parkinson disease

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28
Q

Kartagener Syndrome

A

primary ciliary dyskinesia

  • immotile cilia due to a dynein arm defect
  • male (immotile sperm)and female (dysfunctional fallopian tube cilia) infertility
  • cause bronchiectasis, recurrent sinusitis, and situs inversus
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29
Q

Histochemical Stain for Intermediate Filament: Vimentin

A

Connective Tissue

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30
Q

Histochemical Stain for Intermediate Filament: Desmin

A

Muscle

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31
Q

Histochemical Stain for Intermediate Filament: Cytokeratin

A

Epithelial Cells (keratinized)

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32
Q

Histochemical Stain for Intermediate Filament: GFAP

A

Neuroglia (Astrocytes)

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33
Q

Histochemical Stain for Intermediate Filament: Neurofilaments

A

Neurons

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34
Q

Type I Collagen

A

Bone (made by osteoblasts), skin, tendons;
late wound repair
dec production in osteogenesis imperfecta Type 1

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35
Q

Type II Collagen

A

Cartilage; vitreous body, nucleus pulposus

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36
Q

Type III Collagen

A

Reticulin: skin, blood vessels, uterus, fetal tissue, granulation tissue
Type III: Deficient in the vascular type of Ehlers-Danlos syndrome (ThreE D): this is NOT the common type of Ehlers-Danlos

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37
Q

Type IV Collagen

A 
Basement membrane, basal lamina, lens
Glomeruli of kidney; capsule of lens
Under the FLOOR (basement membrane)
- Defect in Alport syndrome
- targeted by antibodies in Goodpasture Syndrome
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38
Q

Collagen Synthesis (inside fibroblasts)

A
  1. Synthesis (RER): translation of collagen alpha chains (preprocollagen) - usually Gly-X-Y (with X and Y as prline and lysine)
  2. Hydroxylation (RER): Hydroxylation of specific proline and lysine residues (requires vitamin C: deficiency -> scurvy)
  3. Glycosylation (RER): Glycosylation of pro-alpha-chain hydroxylysine residues and formation of procollagen via hydrogen and disulfide bonds (triple helix of 3 collagen alpha chains). Problems –> ostogenesis imperfecta
  4. Exocytosis: of procollagen into extracellular space by Golgi
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39
Q

Collagen Synthesis (outside fibroblasts)

A
  1. Proteolytic Processive: cleavage of disulfide-rich terminal regions of procollage, transforming it into insoluble tropocollagen
  2. Cross-linking: reinforcement of many staggered tropocollagen molecules by covalent lysine-hydroxylysine cross-linkage (by Cu2+ - containing lysyl oxidase) to make collagen fibrils. Problems with cross-linking –> Ehlers-Danlos
40
Q

Ehlers-Danlos Syndrome

A

faulty collagen synthesis: hyperextensible skin, tendency to bleed (easy bruising), and hypermobile joints
- associated with joint dislocation, berry and aortic aneurysms, and organ rupture

41
Q

Menkes Disease

A

connective tissue disease caused by impaired copper absorption and transport. Leads to dec activity of lysyl oxidase (copper is a necessary cofactor).
Brittle, kinky hair, growth retardation and hypotonia

42
Q

Marfan Syndrome

A

defect in fibrillin-1 gene: glycoprotein that forms a sheath around elastin; AD
connective tissue disorder affecting skeleton, heart and eyes. Cystic medial necrosis of aorta –> aortic incompetence and dissecting aortic aneurysms; floppy mitral valve

43
Q

Elastin

A

rich in proline and glycine: nonhydroxylated forms (difference from collagen)

  • stretchy protein with skin, lungs, large arteries, elastic ligaments, vocal cords, ligamenta flava
  • broken down by elastase (which is normally inhibited by alpha-antitrypsin)
44
Q

Variable Expressivity (+ example)

A

Phenotype varies among individuals with same genotype.
2 patients with Neurofibromatosis Type I (NF1) may have varying disease severity. But they both express it to some degree

45
Q

Incomplete Penetrance (+ example)

A

Not all individuals with a mutant genotype show the mutant phenotype.
BRCA1: do not always result in cancer

46
Q

Pleiotropy (+ example)

A

one gene contributes to multiple phenotypic effects

PKU: untreated phenylketonuria manifests with light skin, intellectual disability, and musty body odor.

47
Q

Loss of heterozygosity (+ example)

A

if a patient inherits or develops a mutation in a tumor suppressor gene, the complementary allele must be deleted/mutated before cancer develops
this is NOT true of oncogenes (gain of function mutations)
ex: retinoblastoma and the two-hit hypothesis

48
Q

Dominant Negative Mutation

A

heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning
- mutation of a transcription factor in its allosteric site: nonfunctioning mutant can still bind DNA, preventing the wild-type TF from binding

49
Q

Linkage Disequilibrium

A

tendency for certain alleles at 2 linked loci to occur together more often than expected by change

50
Q

Mosaicism (+ example)

A

presence of genetically distinct cell lines in the same individuals: arises form mitotic errors after fertilization
- somatic mosaicism: mutation propagates through multiple tissues or organs
McCune-Albright syndrome: is lethal if the mutation is somatic but survivable if mosaic

51
Q

Locus heterogeneity (+ example)

A

Mutations at different loci can produce a similar phenotype.

Albinism can be caused by different mutations (melanin production or melanin transport)

52
Q

Allelic Heterogeneity (+ example)

A

different mutations in the same locus produce the same phenotype. beta-thalassemia

53
Q

Heteroplasmy

A

present of both normal and mutated mtDNA: resulting in variable expression in mitochondrial inherited disease
- the earlier the mutation occurs, the more cells that have the mutated DNA

54
Q

Polygenic

A

group of non-allelic genes that together influence a phenotypic trait. Multiple factors; Multiple gene inheritance
examples: androgenetic alopecia (male pattern baldness)

55
Q

Imprinting (+ example)

A

one allele is imprinted/inactivated by methylation. with one allele inactivated, deleted of the active allele –> disease
Prader-Willi and Angelman Syndrome

56
Q

Uniparental Disomy

A

offspring receives 2 copies of chromosome from one parent and no copies from the other

  • heterodisomy: indicates a meiosis I error
  • isodisomy: indicates a meiosis II error
57
Q

Prader-Willi Syndrome

A

maternal imprinting
Paternal gene is deleted/mutated and maternal gene is normally silent
- results in hyperphagia, obesity, intellectual disability, hypogonadism, and hypotonia

58
Q

Angelman Syndrome

A

paternal imprinting
Maternal gene is deleted/mutated and gene from dad is normally silent
- results in inappropriate laughter (happy puppet), seizures, ataxia, and severe intellectual disability

59
Q

Mitochondrial Myopathies

A

mitochondrial inheritance:
- myopathy, lactic acidosis and CNS disease
secondary to failure in oxidative phosphorylation
– muscle biopsy shows “ragged red fibers”

60
Q

Hypophosphatemic Rickets

A

inherited disorder resulting in increased phosphate wasting at proximal tubule
X linked dominant

61
Q

Cystic Fibrosis

A

Autosomal Recessive mutation in CFTR (chr 7): Deletion of Phe508. Misfolded protein.
ATP-gated Cl- channel that secretes Cl- in lungs and GI tract and reabsorbs Cl- in sweat glands.

62
Q

Duchenne Muscular Dystrophy

A

X-linked frameshift mutation (deleted dystrophin: DMD)

- pseudohypertrophy of calf muscles

63
Q

Becker Muscular Dystrophy

A

X-linked point mutation

onset in adolescence or early adulthood

64
Q

22q11 Deletion

A

CATCH-22
Cleft Palate; Abnormal Facies; Thymic aplasia (T cell deficiency); Cardiac defects; Hypocalcemia (secondary to parathyroid aplasia)

65
Q

Kwashiorkor

A 
protein malnutrition resulting in skin lesions, edema, liver malfunction (fatty changes due to dec apolipoprotein synthesis)
- small child with swollen belly
results from protein deficient MEAL:
Malnutrition
Edema
Anemia
Liver (fatty)
66
Q

Marasmus

A

total calorie malnutrition: tissue and muscle wasting, loss of subcutaneous fat and variable edema
Marasmus results in Muscle wasting

67
Q

RDE: Glycolysis

A

phosphofructokinase-1
+ AMP, fructose-2,6-bisphosphate
- ATP, citrate

68
Q

RDE: Gluconeogenesis

A

fructose-1,6-bisphosphatase
+ ATP, acetyl-CoA
- AMP, fructose-2,6-bisphosphate

69
Q

RDE: TCA Cycle

A

isocitrate dehydrogenase
+ ADP
- ATP, NADH

70
Q

RDE: Glycogenesis

A

Glycogen synthase
+ glucose-6-phosphate, insulin, cortisol
- glucose-6-phosphate, glucagon

71
Q

RDE: Glycogenolysis

A

Glycogen phosphorylase
+ epinephrine, glucagon, AMP
- glucose-6-phosphate, insulin, ATP

72
Q

RDE: HMP Shunt

A

glucose-6-phosphate dehydrogenase (G6PD)
+ NADP+
- NADPH

73
Q

RDE: de novo pyrimidine synthesis

A

carbamoyl phosphate synthetase II

74
Q

RDE: de novo purine synthesis

A

glutamine-phosphoribosylpyrophosphate (PRPP) amidotransferase
- AMP, IMP (inosine monophosphate), GMP

75
Q

RDE: Urea cycle

A

carbamoyl phsophate synthetase I

+ N-acetylglutamate

76
Q

RDE: Fatty acid synthesis

A

acetyl-CoA carboxylase (ACC)
+ insulin, citrate
- glucagon, palmitoyl-CoA

77
Q

RDE: Fatty acid oxidation

A

Carnitine acyltransferase I

- malonyl-CoA

78
Q

RDE: Ketogenesis

A

HMG-CoA synthase

79
Q

RDE: Cholesterol Synthesis

A

HMG-CoA reductase
+ insulin, thyroxine
- glucagon, cholesterol

80
Q

Hexokinase

A

most tissues; high affinity but low Vmax (capacity)

- can work when there are tiny amounts of glucose

81
Q

Glucokinase

A

liver only; most active post meal

low affinity but high Vmax

82
Q

Rotenone

A

inhibits Complex I of ETC

causes dec proton gradient and block of ATP synthesis

83
Q

Antimycin A

A

inhibits Complex III of ETC

causes dec proton gradient and block of ATP synthesis

84
Q

Cyanide

A

inhibits Complex IV of ETC

causes dec proton gradient and block of ATP synthesis

85
Q

Carbon Monoxide

A

inhibits Complex IV of ETC

causes dec proton gradient and block of ATP synthesis

86
Q

Oligomycin

A

inhibits Complex V of ETC (ATP synthase).

No ATP is produced as the chain stops

87
Q

Uncoupling Agents

A

increase permeability of mitochondria membrane: causing dec in proton gradient and inc O2 consumption. ATP synthesis stops but electron transport continues. Produces heat

88
Q

Pleiotropy (+ example)

A

One gene contributes to multiple phenotypic effects. Untreated phenylketonuria: light skin, intellectual disability, and musty body order. Homocysteinuria is another.

89
Q

Genetic Heterogeneity

A

mutation of different genes causes similar phenotype (this is NOT allelic heterogeneity: SAME locus/different mutation)

90
Q

Allelic Heterogeneity

A

different mutation at the SAME locus produce similar phenotype (beta-thalassemia)

91
Q

Locus Heterogeneity

A

same as genetic hetergeneity (mutation of different genes causes similar phenotype).

92
Q

Polygenic

A

Polygene, multiple factor, multiple genes in inheritance. Group of non-allelic genes that together influence a phenotypic trait. Ex: androgenetic alopecia (male pattern baldness)

93
Q

ApoA-I

A

LCAT activation (cholesterol esterification)

94
Q

ApoB-48

A

Chylomicron assembly and secretion by the intestine

95
Q

ApoB-100

A

LDL particle uptake by extrahepatic cells

96
Q

ApoC-II

A

Lipoprotein lipase activation

97
Q

ApoE3 and 4

A

VLDL and chylomicron remnant uptake by liver cells

USMLE Step 1 (8 decks)

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