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USMLE > One Word_Biochemistry > Flashcards

One Word_Biochemistry Flashcards

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USMLE® Step 1 flashcards
1
Q

α-amanitin

A

(found in death cap mushrooms) inhibits RNA polymerase II. Causes liver failure if ingested

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2
Q

Zinc

A

Function: Essential for the activity of 100+ enzymes. Important in the formation of zinc fingers (transcription factor motif) Deficiency: Delayed wound healing, hypogonadism, ↓ adult hair (axillary, facial, pubic), dysgeusia, anosmia. May predispose to alcoholic cirrhosis.

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3
Q

Type IV collagen (3)

A

Basement membrane or basal lamina (maybe lens?)

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4
Q

Type III collagen - Reticulin (5)

A

skin, blood vessels, uterus, fetal tissue, granulation tissue

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5
Q

Type II collagen (3)

A

Cartilage (including hyaline), vitreous body, nucleus pulposus

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6
Q

Type I collagen (7)

A

Bone, Skin, Tendon, dentin, fascia, cornea, late wound repair

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7
Q

Trinucleotide repeat expansion diseases

A

Huntington’s disease = (CAG)n Myotonic dystrophy = (CTG)n Fragile X syndrome = (CGG)n Friedreich’s ataxia = (GAA)n

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8
Q

Treatment: Pyruvate dehydrogenase deficiency

A

Lysine and Leucine - the only purely ketogenic amino acids

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9
Q

Treatment: Orotic aciduria

A

Oral uridine administration

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10
Q

Transversion

A

Substituting purine for pyrimidine or vice versa

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11
Q

Transition

A

Substituting purine for purine or pyrimidine for pyrimidine

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12
Q

Toxicity: Arsenic

A

inhibits lipoic acid, causes vomiting, rice water stools, garlic breath

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13
Q

Rate-determining enzymes of metabolic processes - Urea cycle

A

Carbamoyl phosphate synthetase I

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14
Q

Rate-determining enzymes of metabolic processes - TCA cycle

A

Isocitrate dehydrogenase

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15
Q

Rate-determining enzymes of metabolic processes - Ketogenesis

A

HMG-CoA synthase

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16
Q

Rate-determining enzymes of metabolic processes - HMP shunt

A

Glucose-6-phosphate dehydrogenase (G6PD)

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17
Q

Rate-determining enzymes of metabolic processes - Glycolysis

A

Phosphofructokinase-1 (PFK-1)

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18
Q

Rate-determining enzymes of metabolic processes - Glycogenolysis

A

Glycogen phosphorylase

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19
Q

Rate-determining enzymes of metabolic processes - Glycogen synthesis

A

Glycogen synthase

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20
Q

Rate-determining enzymes of metabolic processes - Gluconeogenesis

A

Fructose-1,6-biphosphatase

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21
Q

Rate-determining enzymes of metabolic processes - Fatty acid synthesis

A

Acetyl-CoA carboxylase (ACC)

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22
Q

Rate-determining enzymes of metabolic processes - Fatty acid oxidation

A

Carnithine acyltransferase I

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23
Q

Rate-determining enzymes of metabolic processes - De novo pyrimidine synthesis

A

Carbamoyl phosphate synthetase II

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24
Q

Rate-determining enzymes of metabolic processes - De novo purine synthesis

A

Glutamine-PRPP amidotransferase

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25
Q

Rate-determining enzymes of metabolic processes - Cholesterol synthesis

A

HMG-CoA reductase

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26
Q

Pyruvate dehydrogenase complex

A

The complex contains 3 enzymes that require 5 cofactors: 1. Pyrophosphate (B1); 2. FAD (B2); 3. NAD (B3); 4. CoA (B5); 5. Lipoic acid Activated by exercise: ↑NAD+/NADH ratio, ↑ADP, ↑Ca2+

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27
Q

Pyrimidines are made from?

A

Orotate precursor, with PRPP added later

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28
Q

Purines are made from?

A

IMP precursor

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29
Q

Prader-Willi syndrome

A

Deletion of normally active Paternal allele Mental retardation, hyperphagia, obesity, hypogonadism, hypotonia

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30
Q

Ornithine transcarbamoylase deficiency

A

(↓urea cycle), leads to an accumulation of carbamoyl phosphate, which is then converted to orotic acid

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31
Q

Octamer subunit amino acids

A

Lysine and Arginine

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32
Q

Nucleotide that has a methyl

A

Thymine

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33
Q

Nucleotide that has a ketone

A

Guanine

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34
Q

mRNA start codons code for?

A

Eukaryotes: Methionine Prokaryotes: Formyl-methionine (f-Met)

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35
Q

Molecular motor proteins: Kinesin

A

anterograde to microtubule

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36
Q

Molecular motor proteins: Dynein

A

retrograde to microtubule

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37
Q

Modes of inheritance - Mitochondrial myopathies

A

Mitochondrial inheritance

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38
Q

Modes of inheritance - Leber’s hereditary optic neuropathy

A

Mitochondrial inheritance, degeneration of retinal ganglion cells and axons. Leads to acute loss of central vision.

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39
Q

Modes of inheritance - Hypophosphatemic rickets

A

formerly known as vitamin D resistant rickets. Inherited X-linked dominant disorder resulting in ↑ phosphate wasting at proximal tubule. Results in rickets-like presentation.

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40
Q

MOA: Trimethoprim

A

inhibits bacterial dihydrofolate reductase (↓dTMP)

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41
Q

MOA: Tetracyclines

A

bind 30S subunit, preventing attachment of aminoacyl-tRNA

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42
Q

MOA: Quabain

A

inhibits by binding to K+ site

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43
Q

MOA: Orotic aciduria

A

Inability to convert orotic acid to UMP (de novo pyrimidine synthesis pathway) due to defect in either orotic acid phosphoribosyltransferase or ototidine 5’-phosphate decarboxylase. Autosomal recessive.

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44
Q

MOA: Methotrexate (MTX)

A

inhibits dihydrofolate reductase (↓dTMP)

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45
Q

MOA: Macrolides

A

bind 50S, blocking translocation

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46
Q

MOA: Hydroxyurea

A

inhibits ribonucleotide reductase

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47
Q

MOA: Clindamycin

A

binds 50S, blocking translocation

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48
Q

MOA: Chloramphenicol

A

inhibits 50S peptidyltransferase

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49
Q

MOA: Cardiac glycosides (digoxin and digitoxin)

A

directly inhibit the Na+-K+ ATPase, which leads to indirect inhibition of Na+/Ca2+ exchange. ↑ [Ca2+]i → ↑ cardiac contractility.

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50
Q

MOA: Aminoglycosides

A

inhibit formation of the initiation complex and cause misreading of mRNA

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51
Q

MOA: 6-mercaptopurine (6-MP)

A

blocks de novo purine synthesis

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52
Q

MOA: 5-fluorouracil (5-FU)

A

inhibits thymidylate synthase (↓dTMP)

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53
Q

Metabolism sites - Mitochondria (4)

A

Fatty acid oxidation (β-oxidation), acetyl-CoA production, TCA cycle, oxidative phosphorylation

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54
Q

Metabolism sites - Cytoplasm (5)

A

Glycolysis, fatty acid synthesis, HMP shunt, protein synthesis (RER), steroid synthesis (SER)

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55
Q

Metabolism sites - Both (3)

A

Heme synthesis, Urea cycle, Gluconeogenesis (HUGs takes two)

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56
Q

Marfan’s syndrome

A

caused by a defect in fibrillin

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57
Q

Marasmus

A

energy malnutrition resulting in tissue and muscle wasting, loss of subcutaneous fat, and variable edema.

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58
Q

Major apolipoproteins - E

A

Mediates extra (remnant) uptake

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59
Q

Major apolipoproteins - C-II

A

Cofactor for lipoprotein lipase

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60
Q

Major apolipoproteins - B-48

A

Mediates chylomicron secretion

61
Q

Major apolipoproteins - B-100

A

Binds to LDL receptor, mediates VLDL secretion

62
Q

Major apolipoproteins - A-I

A

Activates LCAT

63
Q

Lysosomal storage diseases - Tay-Sachs disease

A

Findings: Progressive neurodegeneration, developmental delay, cherry-red spot on macula, lysosomes with onion skin, no hepatosplenomegaly (vs. Niemann-Pick) Deficient enzyme: Hexosaminidase A Accumulated substrate: GM2 ganglioside Inheritance: AR

64
Q

Lysosomal storage diseases - Niemann-Pick disease

A

Findings: Progressive neurodegeneration, hepatosplenomegaly, cherry-red spot on macula, foam cells Deficient enzyme: Sphingomyelinase Accumulated substrate: Sphingomyelin Inheritance: AR

65
Q

Lysosomal storage diseases - Metachromatic leukodystrophy

A

Findings: Central and peripheral demyelination with ataxia, dementia Deficient enzyme: Arylsulfatase A Accumulated substrate: Cerebroside sulfate Inheritance: AR

66
Q

Lysosomal storage diseases - Krabbe’s disease

A

Findings: Peripheral neuropathy, developmental delay, optic atrophy, globoid cells Deficient enzyme: Galactocerebrosidase Accumulated substrate: Galactocerebroside Inheritance: AR

67
Q

Lysosomal storage diseases - Hurler’s syndrome

A

Findings: Developmental delay, gargoylism, airway obstruction, corneal clouding, hepatosplenomegaly Deficient enzyme: α-L-iduronidase Accumulated substrate: Heparan sulfate, dermatan sulfate Inheritance: AR

68
Q

Lysosomal storage diseases - Hunter’s syndrome

A

Findings: Mild Hurler’s + aggressive behavior, no corneal clouding Deficient enzyme: Iduronate sulfatase Accumulated substrate: Heparan sulfate, dermatan sulfate Inheritance: XR

69
Q

Lysosomal storage diseases - Gaucher’s disease (most common)

A

Findings: Hepatosplenomegaly, aseptic necrosis of the femur, bone crisis, Gaucher’s cells (macrophages that look like crumpled tissue paper) Deficient enzyme: β-glucocerebrosidase Accumulated substrate: Glucocerebroside Inheritance: AR

70
Q

Lysosomal storage diseases - Fabry’s disease

A

Findings: Peripheral neuropathy of hands/feet, angiokeratomas, cardiovascular/renal disease Deficient enzyme: α-galactosidase A Accumulated substrate: Ceramide trihexoside Inheritance: XR

71
Q

Liver enzyme - Pancreatic lipase

A

degradation of dietary TG in small intestine

72
Q

Liver enzyme - Lipoprotein lipase (LPL)

A

degradation of TG circulating in chylomicrons and VLDLs

73
Q

Liver enzyme - Hormone-sensitive lipase

A

degradation of TG stored in adipocytes

74
Q

Liver enzyme - Hepatic TG lipase (HL)

A

degradation of TG remaining in IDL

75
Q

Lesch-Nyhan syndrome

A

X-linked recessive, defective purine salvage owing to absence of HGPRT, which converts hypoxanthine to IMP and guanine to GMP. Results in excess uric acid production. Findings: retardation, self-mutilation, aggression, hyperuricemia, gout, choreoathetosis

76
Q

Kwashiokor

A

protein malnutrition resulting in skin lesions, edema, liver function (fatty change due to ↓ apolipoprotein synthesis). Clinical picture is a small child with swollen belly. Malnutrition, Edema, Anemia, fatty Liver.

77
Q

Kartagener’s syndrome

A

immotile cilia due to a dynein arm defect. Results in male and female infertility (sperm immotile), bronchiectasis, and recurrent sinusitis (bacteria and particles not pushed out); associated with situs inversus

78
Q

Imprinting

A

At a single locus, only 1 allele is active; the other is inactive (imprinted / inactivated by methylation). Deletion of the active allele → disease Both syndromes due to inactivation or deletion of genes on chromosome 15 Can also occur as a result of uniparental disomy

79
Q

Immunohistochemical stains: Vimentin

A

Connective tissue

80
Q

Immunohistochemical stains: Neurofilaments

A

Neurons

81
Q

Immunohistochemical stains: GFAP

A

Neuroglia

82
Q

Immunohistochemical stains: Desmin

A

Muscle

83
Q

Immunohistochemical stains: Cytokeratin

A

Epithelial cells

84
Q

I-cell disease

A

(inclusion cell disease) - inherited lysosomal storage disorder; failure of addition of mannose-6-phosphate to lysosome proteins (enzymes are secreted outside the cell instead of being targeted to the lysosome). Results in coarse facial features, clouded corneas, restricted joint movement, and high plasma levels of lysosomal enzymes. Often fatal in childhood.

85
Q

Heterochromatin

A

Condensed, transcriptionally inactive, sterically inaccessible

86
Q

Hardy-Weinberg law assumptions (4)

A
  1. No mutation occuring at the locus 2. No selection for any of the genotypes at the locus 3. Completely random mating 4. No migration
87
Q

Glycogen storage diseases - Von Gierke’s disease (type I)

A

Findings: severe fasting hypoglycemia, ↑↑ glycogen in liver, ↑ blood lactate, hepatomegaly Deficient enzyme: Glucose-6-phosphatase

88
Q

Glycogen storage diseases - Pompe’s disease (Type II)

A

Findings: Cardiomegaly and systemic findings leading to early death Deficient enzyme: Lysosomal α-1,4-glucosidase (acid maltase)

89
Q

Glycogen storage diseases - McArdle’s disease (type V)

A

Findings: ↑ glycogen in muscle, but cannot break it down, leading to painful muscle cramps, myoglobinuria with stenuous exercise Deficient enzyme: Skeletal muscle glycogen phosphorylase

90
Q

Glycogen storage diseases - Cori’s disease (type III)

A

Findings: milder form of type I with normal blood lactate levels Deficient enzyme: Debranching enzyme (α-1,6-glucosidase)

91
Q

Genetic terms: Variable expression

A

Nature and severity of phenotype vary from 1 individual to another

92
Q

Genetic terms: Uniparental disomy

A

Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent

93
Q

Genetic terms: Pleiotropy

A

1 gene has > 1 effect on an individual’s phenotype

94
Q

Genetic terms: Mosaicism

A

Occurs when cells in the body have different genetic makeup. Can be a germ-line mosaic, which may produce disease that is not carried by parent’s somatic cells

95
Q

Genetic terms: Loss of heterozygosity

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.

96
Q

Genetic terms: Locus heterogeneity

A

Mutations at different loci can produce the same phenotype

97
Q

Genetic terms: Linkage disequilibrium

A

Tendency for certain alleles at 2 linked loci to occur together more often than expected by chance. Measured in a population, not in a family, and often varies in different populations.

98
Q

Genetic terms: Incomplete penetrance

A

Not all individuals with a mutant genotype show the mutant phenotype

99
Q

Genetic terms: Imprinting

A

Differences in phenotype depend on whether the mutation is of maternal or paternal origin

100
Q

Genetic terms: Heteroplasmy

A

Presence of both normal and mutated mtDNA, resulting in variable expression in mitochondial inherited disease.

101
Q

Genetic terms: Dominant negative mutation

A

Exerts a dominant effect. A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning.

102
Q

Genetic terms: Codominance

A

Neither of 2 alleles is dominant

103
Q

Genetic terms: Anticipation

A

Severity of disease worsens or age of onset of disease is earlier in succeeding generations

104
Q

Genetic code features: Universal

A

Genetic code is conserved throughout evolution

105
Q

Genetic code features: Unambiguous

A

Each codon specifies only 1 amino acid

106
Q

Genetic code features: Degenerate / redundant

A

More than 1 codon may code for the same amino acid

107
Q

Genetic code features: Commaless, nonoverlapping

A

Read from a fixed starting point as a continuous sequence of bases

108
Q

Findings: Orotic aciduria

A

↑ orotic acid in urine, megaloblastic anemia (does not improve with administration of vitamin B12 or folic acid), failure to thrive. No hyperammonemia (vs. OTC deficiency - ↑ orotic acid with hyperammonemia)

109
Q

Euchromatin

A

Less condensed, transcriptionally active, sterically accessible

110
Q

Ethanol metabolism: Fomepizole

A

inhibits alcohol dehydrogenase and is an antidote for methanol of ethylene glycol poisoning

111
Q

Ethanol metabolism: Disulfiram (Antabuse)

A

inhibits acetaldehyde dehydrogenase (acetaldehyde accumulates, contributing to hangover symptoms)

112
Q

Emphysema

A

can be caused by α1-antitrypsin deficiency, resulting in excess elastase activity

113
Q

Elastin

A

Stretchy protein within lungs, large arteries, elastic ligaments, vocal cords, ligamenta flava (connect vertebrae → relaxed and stretched conformations). √. Rich in proline and glycine, nonglycosylated forms. √. Tropoelastin with fibrillin scaffolding. √. Broken down by elastase, which is normally inhibited by α1-antitrypsin.

114
Q

Drugs that act on microtubules

A
  1. Mebendazole / thiabendazole (antihelminthic) 2. Griseofulvin (antifungal) 3. Vincristine / vinblastine (anti-cancer) 4. Paclitaxel (anti-breast cancer) 5. Colchicine (anti-gout)
115
Q

DNA replication: Single-stranded binding proteins

A

Prevent strands from reannealing

116
Q

DNA replication: Replication disk

A

Y-shaped region alond DNA template where leading and lagging strands are synthesized

117
Q

DNA replication: Proofreads

A

DNA polymerase III has 5’ → 3’ synthesis and proofreads with 3’ → 5’ exonuclease DNA polymerase I excises RNA primer with 5’ → 3’ exonuclease

118
Q

DNA replication: Primase

A

Makes an RNA primer on which DNA polymerase III can initiate replication

119
Q

DNA replication: Origin of replication

A

Particular sequence in genome where DNA replication begins. May be single (prokaryotes) or multiple (eukaryotes)

120
Q

DNA replication: Helicase

A

Unwinds DNA template at replication fork

121
Q

DNA replication: DNA topoisomerases

A

Create a nick in the helix to relieve supercoils created during replication

122
Q

DNA replication: DNA polymerase III

A

Prokaryotic only. Elongates leading strand by adding deoxynucleotides to the 3’ end. Elongates lagging strand until it reaches primer of preceeding fragment. 3’ → 5’ exonuclease activity “proofreads” each added nucleotide

123
Q

DNA replication: DNA polymerase I

A

Prokaryotic only. Degrades RNA primer and fills in the gap with DNA

124
Q

DNA replication: DNA ligase

A

Seals

125
Q

DNA repair: Nucleotide excision repair

A

Specific endonucleases release the oligonucleotide containing damaged bases; DNA polymerase and ligase fill and reseal the gap, respectively. Mutated in xeroderma pigmentosum

126
Q

DNA repair: Nonhomologous end joining

A

Brings together 2 ends of DNA fragments. No requirement for homology

127
Q

DNA repair: Mismatch repair

A

Unmethylated, newly synthesized string is recognized, mismatched nucleotides are removed, and the gap is filled and resealed. Mutated in Hereditary nonpolyposis colorectal cancer (HNPCC)

128
Q

DNA repair: Base excision repair

A

Specific glycosylases recognize and remove damaged bases, AP endonuclease cuts DNA at apyrimidinic site, empty sugar is removed, and the gap is filled and resealed.

129
Q

Cytoskeletal elements: Microtubule (5)

A

Cilia, flagella, mitotic spindle, neurons, centrioles

130
Q

Cytoskeletal elements: Intermediate filaments (5)

A

Vimentin, desmin, cytokeratin, glial fibrillary acid proteins (GFAP), neurofilaments

131
Q

Cytoskeletal elements: Actin and myosin (4)

A

Microvilli, muscle contraction, cytokinesis, adherens junctions

132
Q

Chédiak-Higashi syndrome

A

microtubule polymerization defect resulting in ↓ phagocytosis. Results in recurrent pyogenic infections, partial albinism, and peripheral neuropathy

133
Q

Carbamoyl phosphate is involved in which 2 metabolic pathways?

A
  1. de novo pyrimidine synthesis 2. urea cycle
134
Q

Autosomal dominant diseases - von Hippel-Lindau disease

A

Findings: hemangioblastomas of retina/cerebellum/medulla; about half of affected individuals develop multiple bilateral renal cell carcinomas and other tumors. Associated with deletion of VHL gene (tumor suppressor) on chromosome 3 (3p). Results in constitutive expression of HIF (transcription factor) and activation of angiogenic growth factors. Von Hippel-Lindau = 3 words for chromosome 3.

135
Q

Autosomal dominant diseases - Tuberous sclerosis

A

Findings: facial lesions (adenoma sebaceum), hyperpigmented “ash leaf spots” on skin, cortical and retinal hamartomas, seizures, mental retardation, renal cysts and renal angiomyolipomas, cardiac rhabdomyomas, ↑ incidence of astrocytomas. Incomplete penetrance, variable presentation.

136
Q

Autosomal dominant diseases - Neurofibromatosis type 2

A

Bilateral acoustic schwannomas, juvenile cataracts. NF2 gene on chromosome 22; type 2 = 22.

137
Q

Autosomal dominant diseases - Neurofibromatosis type 1 (von Recklinghausen’s disease)

A

Findings: café-au-lait spots, neural tumors, Lisch nodules (pigmented iris hamartomas). Also marked by skeletal disorders (e.g., scoliosis) and optic pathway gliomas. On long arm of chromosome 17; 17 letters in von Recklinghausen.

138
Q

Autosomal dominant diseases - Marfan’s syndrome

A

Fibrillin gene mutation → connective tissue disorder affecting skeleton, heart, and eyes. Findings: tall with long extremities, pectus excavatum, hyperextensive joints, and long, tapering fingers and toes (arachnodactyly); cystic medial necrosis of aorta → aortic incompetence and dissecting aortic aneurysms; floopy mitral valve. Subluxation of lenses.

139
Q

Autosomal dominant diseases - Huntington’s disease

A

Findings: depression, progressive dementia, choreiform movements, caudate atrophy, and ↓ levels of GABA and ACh in the brain. Symptoms manifest in affected individuals between the ages 20 and 50. Gene located on chromosome 4; trinucleotide repeat disorder: (CAG)n. “Hunting 4 food”

140
Q

Autosomal dominant diseases - Hereditary spherocytosis

A

Spheroid erythrocytes due to spectrin or ankyrin defect; hemolytic anemia; ↑ MCHC. Splenectomy is curative.

141
Q

Autosomal dominant diseases - Hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome)

A

Inherited disorder of blood vessels. Findings: telangiectasia, recurrent epistaxis, skin discolorations, arteriovenous malformations (AVMs).

142
Q

Autosomal dominant diseases - Familial hypercholesterolemia (hyperlipidemia type IIA)

A

Elevated LDL due to defective or absent LDL receptor. Heterozygotes (1:500) have cholesterol ≈ 300mg/dL. Homozygotes (very rare) have cholesterol ≈ 700+mg/dL, severe atherosclerotic disease early in life, and tendon xanthomas (classically in the Achilles tendon); MI may develop before age 20.

143
Q

Autosomal dominant diseases - Familial adenomatous polyposis

A

Colon becomes covered with adenomatous polyps after puberty. Progresses to colon cancer unless resected. Mutation on chromosome 5 (APC gene); 5 letters in “polyp”.

144
Q

Autosomal dominant diseases - Autosomal-dominant polycystic kidney disease (ADPKD)

A

Formerly known as adult polycystic kidney disease. Always bilateral, massive enlargement of kidneys due to multiple large cysts. Patients present with flank pain, hematuria, hypertension, progressive renal failure. 90% of cases are due to mutation in APKD1 (chromosome 16; 16 letters in “polycystic kidney”). Associated with polycystic liver disease, berry aneurysms, mitral valve prolapse. Infantile form is recessive.

145
Q

Autosomal dominant diseases - Achondroplasia

A

Cell-signaling defect of fibroblast growth factor (FGF) receptor 3. Results in dwarfism; short limbs, but head and trunk are normal size. Associated with advanced paternal age.

146
Q

Angelman’s syndrome

A

Deletion of normally active maternal allele Mental retardation, seizures, ataxia, inappropriate laughter (“happy puppet”)

147
Q

Amino acids necessary for purine synthesis

A

Glycine, Aspartate, Glutamine

148
Q

Adenosine deaminase deficiency

A

Excess ATP and dATP imbalances nucleotide pool via feedback inhibition of ribonucleotide reductase → prevents DNA synthesis and thus ↓ lymphocyte count. One of the major causes of SCID.

USMLE (12 decks)

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