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Dr. Mel - Biochemistry > UWorld 2017 > Flashcards

UWorld 2017 Flashcards

1
Q

Methylmalonic acidemia

A

Deficiency of methylmalonyl-CoA mutase
Lethargy, tachypnea, vomiting (newborn)
Hyperammonemia, ketotic hypoglycemia, metabolic acidosis
Urine: elevated methylmalonic acid + propionic acid

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2
Q

5 precursors of Propionyl-CoA + 4 symptoms of propionyl acidemia

A

Valine, isoleucine, methionine, threonine, odd-chain fatty acids

Lethargy, vomiting, poor feeding, hypotonia (1-2w after birth)

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3
Q

Classic galactosemia

A

Galactose-1-phosphate uridyl transferase (GALT) deficiency
Few days after breastfeeding
Vomiting, lethargy, jaundice, hepatomegaly, renal dysfunction, E coli sepsis
Ttt: cessation of breastfeeding + switching to soy milk-based formula

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4
Q

Fabry disease

A

Alpha-galactosidase A deficiency
Accumulation of globotriaosylceramide
Early: neuropathic pain, angiokeratomas
In adulthood: proteinuria, renal failure, ventricular hypertrophy, transient ischemic attack, stroke

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5
Q

Lead toxicity

A

Inhibition of ferrochelatase + D-ALA dehydratase
Anemia, ALA accumulation, high zinc protoporphyrin
Neurotoxicity (long-terme)

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6
Q

Fragile X syndrome

A

Often w/ developmental delay + neuropsychiatric findings

Anxiety disorders, autism, ADHD

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7
Q

Adhesin of cells to extracellular matrix

A

Integrin binding to fibronectin / collagen / laminin

Differential expression of integrin subtypes correlates w/ malignant behavior (ex: melanoma)

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8
Q

Base excision repair

A

Correct single-base DNA defects

By glycosylase - endonuclease + lyase - polymerase - ligase

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9
Q

Vitamin B12 deficiency

A 
Megaloblastic anemia (impaired DNA synthesis)
Neurologic def (impaired myelin synthesis): subacute combined degeneration of dorsal columns + lat corticospinal tract
High methylmalonic acid + homocysteine
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10
Q

Impaired tetrahydrobiopterin (BH4)

A

Esp by DH4 reductase deficiency

Account for 2% of phenylcetonuria

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11
Q

Vitamin A overuse

A

Intracranial HTN
Skin changes
Hepatosplenomegaly

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12
Q

Regulation of Ras-MAPK signal transduction

A

Balance: Ras protein GTP-bound (active) + GDP-bound (inactive)
RAS gene mutation: activated Ras protein (dev of cancer)

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13
Q

DNA polymerase I function in prokaryotes

A

5’ to 3’ exonuclease: removes RNA primase + repair damaged DNA
3’ to 5’ exonuclease
5’ to 3’ polymerase

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14
Q

RBC’s inability to synthesize heme

A

If mitochondrial loss

Mito necessary for first + final 3 steps of heme synthesis

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15
Q

Alkaptonuria

A 
Lack of homogentisic acid dioxygenase
Blocking metab of tyrosine
Accumulation of homogentisic acid
Black urine when exposed to air
Blue-black pigm on face
Ochronotic arthropathy
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16
Q

microRNA + siRNA

A

Short non-coding RNA sequences
Base-pairing w/ complementary sequences in mRNA
Induce posttranscriptional gene silencing

17
Q

Hartnup disease

A

Impaired transport of neutral aa
Niacin deficiency
Pellagra-like skin eruptions, cerebellar ataxia
Dg: excessive neutral aa in urine

18
Q

Principal stabilizing force of secondary structure of proteins

A

Hydrogen bonds

19
Q

Synchronization of glycogen degradation w/ skeletal muscle contraction

A

Due to release of sarcoplasmic Ca2+
Increased intracellular Ca2+: activation of phosphorylase kinase, stimulation of glycogen phosphorylase, increased glycogenolysis

20
Q

Pompe disease

A

Acid maltase (alpha-glucosidase) deficiency
Abnl glycogen accumulation in lysosomes of muscles
Early infancy
Cardiomegaly, macroglossia, profound muscular hypotonia

21
Q

Congenital def of propionyl-CoA carboxylase

A

Enzyme converts propionyl-CoA to methylmalonyl-CoA
Propionyl-CoA from metab of valine, isoleucine, methionine, threonine, odd-chain fatty acids
Enz def: propionic acidemia - lethargy, poor feeding, vomiting, hypotonia (1-2w after birth)

22
Q

Hepatic encephalopathy

A

Hyperammonemia in adv liver failure
Ammonia crosses BBB: excess glutamine accumulate in astrocytes
Decreased glutamine for conversion to glutamate in neurons: disruption of excitatory neurotransmission

23
Q

Cause of diff clinical severity betw/ HbS and HbC

A

HbS: valine in place of glutamic acid

Hydrophobic interaction in Hb + HbS polymerization (sickling)

24
Q

Increased Fructose 2,6-biphosphate in hepatocytes

A

Inhibit conversion of Alanine to glucose
F2,6BP activates PFK-1 (increased glycolysis) + inhibits fructose 1,6-biphosphatase (decreasing gluconeogenesis)
Insulin activates phosphofructokinase-2 that increases F2,6BP
Glucagon activates fructose 2,6-biphosphatase that decreases F2,6BP

25
Q

Pentose phosphate pathway

A

Oxidative (irreversible) + nonoxidative (reversible)

Transketolase: for interconversion of ribose-5-phosphate and fructose-6-phosphate

26
Q

3’ CCA tail of tRNA

A

Is amino acid binding site

Aminoacyl tRNA synthetase: for loading the appropriate aa to 3’CCA tail

27
Q

Abetalipoproteinemia

A

Inability to synthesize apolipopB
Lipids absorbed but not transported into blood
Accumulate in intest epith = enterocytes + clear/foamy cytoplasm

28
Q

Phenylketonuria

A

Phenylalanine hydroxylase deficiency
Tetrahydrobiopterin defiency
Accumulation of phenylalanine in body fluids + CNS
Homozygous: normal at birth then severe intellect disability+seizures
Hipopigm: skin, hair, eyes, catechol brain nuclei (substantia nigra, locus ceruleus, vagal nucleus dorsalis)

29
Q

Chronic thiamine deficiency

A

Decreased activity of enzymes w/ B1 cofactor
Pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, transketolase
Impaired glucose utilization in CNS
B1 def dg if erythrocyte transketolase activity is low and increases after addition of thiamine pyrophosphate

30
Q

GALT vs GALK deficiencies

A

GALT def: accumulation of galactose-1-phosphate, neonatal presentation, vomiting, lethargy, failure to thrive, hepatic+renal dysfct
GALK: galactose accumulation, late presentation, normal growth, CATARACT (galactitol accum)

31
Q

lac operon regulation

A

Negatively: binding of repressor prot to operator locus
Positively: cAMP-CAP binding upstream from promoter
Expression of lac operon: mutations that impair binding of repressor prot (Lac I) to its regulatory sequence in operator region

32
Q

Vitamin E deficiency

A

Vit E protect fatty acids from oxidation
Vit E def (when fat malabsorption): oxidative injury of cell membranes, esp neurons w/ long axons + erythrocytes
Vit E def manif: neuromusc ds (ataxia, impaired proprioception + vibratory sensation), hemolytic anemia

33
Q

Riboflavin

A

Precursor of coenzymes FMN, FAD
FAD participates in tricarboxylic acid cycle + electron transport chain
FAD acts as electron acceptor for succinate dehydrogenase (complex II) that converts succinate into fumarate

34
Q

Retinoblastoma protein phosphorylation

A

By proliferation signals that activate CDK4
Increases DHF reductase and DNA polymerase activity
Hyperphosphorylated Rb is inactive: cells transition unchecked from G1 to S phase

35
Q

Minor cause of Down sd

A

Unbalanced Robertsonian translocation
2 acrocentric nonhomologus chrom
46, XX or XY, t(14;21)

36
Q

CFTR protein in cystic fibrosis

A

Mutation: DF508, prot misfolding
Failure of glycosylation
Proteasome-mediated degradation
Decreased nb of transmembrane CFTR prot

37
Q

Elastin

A

Extensive cross-linking between monomers
Facilitated by lysyl oxidase
Alpha1-antitrypsin def: early lower lobe emphysema (excessive elastin degradation)

38
Q

Chronic granulomatous ds

A

Mutation in NADPH oxidase
Neutro cant form oxidative burst (kill org in phagolysos)
Dg: absence normal blue by nitroblue tetrazolium test + absence fluo green by dihydrorhodamine flow cytometry test

39
Q

High risk in X-linked agammaglobulinemia

A

Absence of opsonizing/neuralizing Ab: pyogenic bact, enteroviruses, Giardia lamblia

Dr. Mel - Biochemistry (2 decks)

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