Biochemistry Part 3 UWorld Qbank & First Aid

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Name two reactions catalized by aldose reductase.
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Galactose → galactitol; glucose → sorbitol
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4 cell types without sorbitol dehydrogenase:
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Schwann cells, lens, retina, kidneys
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Reaction catalyzed by sorbitol dehydrogenase:
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sorbitol → fructose
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What energy source does the urea cycle require?
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2ATP
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Name the basic amino acids:
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Arginine, lysine, histadine (Arg, Lys are abundant in histones, histine is neutral at physiologic pH)
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Hereditary pattern of ornithine transcarbamolyase deficiency:
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X-linked recessive
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Serotonin is derived from what precursor?
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Tryptophan -(BH2)→ serotonin → melatonin
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Dopa decarboxylase is inhibited in the treatment of what disease?
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Parkinsons; decreases peripheral dopamine synthesis → increases peripheral DOPA which can cross the BBB
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Cofactor in dopamine -(Dopamine beta-hydroxylase)→ norepinephrine reaction
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vitamin C
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What substance regulates phenylethoanolamine N-methyl transferase?
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Cortisol (more norepinephrine → epinephrine during stress)
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Where is epinephrine synthesized?
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Adrenal gland
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2 metabolic diseases that demonstrate locus heterogeneity:
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albinism (tyrosinase defect, tyrosine transport defect, lack of neural crest migration), homocystinuria (cystathionine synthase deficiency, decrased affinity of cystathionine synthase for pyridoxial phosphate (B6), Homocysteine methyltransferase deficiency (B12))
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Inheritance pattern of cystinuria:
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autosomal recessive (defect in PCT amino acid transport)
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Pathway of glucagon (liver) and epinephrine (liver and muscle) signaling:
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bind receptor → increased cAMP → increased protein kinase A → phosphorylation of glycogen phosphorylase kinase → phosphorylation of glycogen kinase → breakdown of glycogen (think phosphorylation)
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Pathway of insulin signaling:
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bind receptor → receptor tyrosine kinase dimerizes → activation of protein phosphatases → dephosphorylation of glycogen phosphorylase kinase and glycogen kinase → decreased breakdown of glycogen (think dephosphorylation)
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Name a lysosomal storage disease that is not autosomal recessive.
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Fabry’s disease and Hunter’s disease are X-linked recessive (Fabry’s: deficient alpha-glactosidease A, accumulation of ceramide trihexoside; Hunters: deficient iduronate sulfatase, accumulation of heparan sulfate, dermatan sulfate)
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Most common lysosomal storage disease:
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Gaucher’s disease; deficiency of glucocerebrosidase, accumulation of glucocerebroside
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Findings in Gaucher’s disease:
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Aseptic necrosis of femur, bone crisis, Gaucher’s cells: macrophages that appear as crumpled paper, hepatosplenomegaly (crying skeleton riding skeleton horse pointing to a crow with a femur)
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Findings in Krabbe’s disease:
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Peripheral neuropathy, developmental delay, optic atrophy, globoid cells (crab on top of the world with sunglasses and axon arms)
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Deficency in Krabbe disease:
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Galactocerebrosidase (accumulation of glalactocerebroside)
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Findings in metachromatic leukodystophy:
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central and peripheral demyelination with ataxia, dementia (Metal Luke shooting an arrow and getting in a taxi with a confused driver) (deficiency of arylsufatase A, build up of cerebroside sulfate)
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Findings in Hurlers syndrome:
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gargoylism, corneal clouding, developmental delay, airway obstruction, hepatosplenomegaly (Hurling gargoyl with corn in his eyes) (Hunter’s syndrome less severe, no corneal clouding and X-linked recessive)
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Enzyme deficiency and substance that accumulates in Hurler’s and Hunter syndrome:
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alpha-L-iduronidase deficiency, accumulation of heparan sulfate and dermatan sulfate (deer pulling hurling gargoyl with corn in his eyes; no corneal clouding in Hunters)
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How does fatty acid synthesis begin?
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Transport of citrate out of the mitochondrial matrix into the cytoplasm via the citrate shuttle (produces and NADPH, which is used in fatty acid synthesis, citrate is then broken down into acetyl-CoA)
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How would carnitine deficiency affect ketone and glucose levels?
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Decrease; increased acyl-CoA would inhibit gluconeogenesis
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How would acyl-CoA dehydrongenase deficiency affect ketone and glucose levels:
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decrease; cannot make ketone bodies and lack energy for gluconeogenesis
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Ketones have the same starting substrate as:
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cholesterol (HMG-CoA)
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What reactions need to occur in order for cholesterol to be packaged into VLDL, IDL, LDL?
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Esterfication catalized by lecithin-cholesterol acyltransferase (allows cholesterol to be stored in vesicles rather than imbedded in the membrane) and then transfer from mature HDL to VLDL, IDL or LDL by a transfer protein
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What lipoprotein is Apo-E not present on?
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LDL
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What enzyme does ApoA-1 activate?
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Lethicin-cholesterol acyltransferase, LCAT (present on HDL and chylomicrons)
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What apolipoprotein is a cofactor of lipoprotein lipase?
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ApoC-II (present on Chylomicrons and VLDL, mediates transfer of TG to adipose tissue)
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What apolipoprotein binds the LDL receptor?
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B-100 (present on VLDL, IDL, LDL)
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What is the function of ApoB-48?
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Mediates chylomicron secretion (present on chylomicron and chylomicron remnant)
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Describe the life of a chylomicron.
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Secreted by intestinal epithelial cells, delivers dietary TGs to peripheral tissue, delivers cholesterol to live in the form of chylomicron remnant
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Name the apoprotein that activates the enzyme necessary to make a mature HDL molecule.
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ApoA-1 activates LCAT
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What is the cause of hyperchylomicronemia?
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LPL deficiency or altered ApoC-II
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Does LPL deficiency or altered ApoC-II seen in hyperchylomicronemia increase the risk for atherosclerosis?
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No; causes pancreatitis, hepatosplenomegaly, and eruptive/pruritic xanthomas
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Name an ocular manifestation of familial hypercholesterolemia.
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Corneal arcus
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Inheritance pattern of familial hypercholesterolemia:
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Autosomal dominant
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Abetalipoproteinemia is due to hereditary inability to synthesize apoB-100 and apoB-48. What is the main cause of symptoms?
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Inability to export absorbed lipid as chylomicrons leads to steatorrhea, failure to thrive, night blindiness, acanthocytosis and ataxia
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What can be seen on peripheral blood smear in patients with abetalipoproteinemia?
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Acanthocytes due to imbalance of membrane components
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Activity of what enzyme is increased in Lesch-Nyhan syndrome?
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PRPP amidotransferase
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Name a treatment for cyanide poisoning.
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Nitrates cause methemoglobin which binds tightly to CN and helps to prevent it from damaging mitochondrial enzymes
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In the cells of the respiratory tract, viral proteins from the influenza virus are degraded and attached to major MHC I molecules that are then expressed on the cell surface for presentation to cytotoxic CD8+ lymphocytes. What enzyme is most likely involved in this process?
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Ubiquitin ligase, which catalyzes ubiquitin attachment
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What is the main cause of fine skin wrinkles in aging?
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Decreased synthesis and net loss of dermal collagen and elastin
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Name a metabolic process inhibited by fructose 2,6-bisphosphate.
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Gluconeogenesis
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Insulin-mediated glucose uptake is primarily present in:
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skeletal muscle cells and adipocytes
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Where are thyroid hormone receptors located?
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Nucleus
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Why does HbS sickle?
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Hydrophobic interaction among hemoglobin molecules; normally all of the hydrophobic amino acids are in the interior
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How does iRNA work?
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Posttranscriptional gene silencing by base-pairing with complementary sequences within target mRNA molecules
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An infant who fails to gain weight has no enteropeptidase activity on the surface of her duodenal epithelium. What substance is most likely impaired as a result?
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Trypsin
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What type of reaction does methylmalonyl CoA undergo to produce succinyl CoA?
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Isomerization
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Where is the cortisol receptor located?
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Cytoplasm; translocates to the nucleus after binding
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How does cortisol affect glucose metabolism?
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Enhances hepatic glucose production and limits peripheral glucose utilization through altering gene transcription (contributes to glucose homeostasis during prolonged fasting along with GH; glucagon with epinephrine as a major backup, is the primary hormone secreted in response to a rapid drop in blood glucose levels
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3 examples of steroid producing cells that have a prominent smooth ER:
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adrenal, gonadal, liver
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Name 4 example of factors that utilize the tyrosine kinase-associated receptors and the JAK/STAT signaling pathway:
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colony-stimulating factors, prolactin, growth hormones, cytokines
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Deletion of a single nucleotide from a DNA sequence results in what type of mutation?
answer

Frameshift
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Name an allosteric activator of pyruvate carboxylase.
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Acetyl-CoA; pyruvate carboxylase catalyses the first step in gluconeogenesis; high acetyl-CoA levels indicate energy excess
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Citrate is an allosteric activator of:
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acetyl-CoA carboxylase (fatty acid synthesis) and fructose-1,6-bispohsphatase
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What type of disorders tends to have a mutation in the cytoplasmic tyrosine kinase, Janus kinase 2 (JAK2)?
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Chronic myeloproliferative disorders including polycythemia vera, essential thrombocytosis and primary myelofibrosis; constitutive tyrosine kinase activity results in cytokine-independent activation of STAT transcription factors
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A 67-year-old man has pallor, early satiety, severe fatigue, 20lbs weight loss over the past 6 months, hepatomegaly and massive splenomegaly. A cytosolic protein in his WBCs has constitutive tyrosine phosphorylation activity. There is persisten activation of STAT protein. What condition does he likely have?
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Primary myelofibrosis
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Most enchancers are located where, with respect to the transcription start site?
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Variable locations
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What serum autoantibodies have a high specificity for rheumatoid arthritis?
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Anti-cyclic citrullinated peptides (anti-CCP)
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Monoamine oxidase normally metabolizes:
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Tyramine
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Tyramine is present in:
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aged cheeses, cured meats, draft beer
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Mechanism of action of tyramine:
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indirect sympathomimetic that is usually metabolized in the intestine by monoamine oxidase (MAO); excess amounts displace norepineprine from vesicles in the presenaptic neuron
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A patient on a monoamine oxidase (MAO) inhibitor who consumes beer and cheese is at risk for developing a:
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hypertensive emergency (sever hypertension, headache, blurry vision) and excessive sympathetic activity (tachycardia, diaphoresis, tremors)

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