biochem questions

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biochem questions
2015-01-25 16:09:43

rx questions
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  1. phosphatidylcholine is formed by donation of methyl groups. _____ is the only amino acid listed that can donate methyl groups. The activated form, ________, is a very common methyl group donor
    • Methionine
    • S-adenosyl-L-methionine (SAM)
  2. Cells exposed to this drug are found to be uniformly arrested in metaphase with intact mitotic spindles.The mechanism of action of this new drug is similar to the action of which of the following drugs?
    Paclitaxel is a chemotherapeutic agent that prevents microtubule depolymerization. This stabilizes the mitotic spindle and disallows the migration of chromatids to their respective ends of the cell. Mitosis remains incomplete, leading to cell death. Paclitaxel is primarily used to treat advanced ovarian cancer and metastatic breast cancer.
  3. The patient appears to have a very large barrel-shaped chest and often purses his lips when he breathes. On examination the physician hears diminished breath sounds. Arterial blood gas analysis shows a partial arterial oxygen pressure of 75 mm Hg and a partial arterial carbon dioxide pressure of 50 mm Hg.As a result of his disease, the substrate of which enzyme has built up in this patient's lungs?
    The excess carbon dioxide in this patient's lungs and blood is caused by the ineffective expirations and air trapping from his COPD. Carbon dioxide is a substrate for carbonic anhydrase, the enzyme in RBCs that catalyzes its conversion to bicarbonate.
  4. Pt w/ abdominal pain, red urine, muscle weakness, and psychiatric manifestations such as anxiety, paranoia, and depression, and high PBG levels in urine
    DX? defective enzyme?
    • Acute intermittent porphyria (AIP)
    • defect in the enzyme porphobilinogen (PBG) deaminase, also called uroporphyrinogen I synthase.
  5. In vitro studies with a hepatocyte cell line revealed that the drug increases the number of LDL cholesterol receptors by acting in a manner similar to that of steroids.What is the mechanism by which this drug is acting on hepatocytes?
    Like steroid hormones, this drug binds to a cytosolic receptor to form a hormone receptor complex. The complex is transported to the nucleus, where it acts (as does a transcription factor) on DNA to increase the transcription of LDL cholesterol receptor messenger RNA, which is translated into LDL receptors. It is important to note that both steroids and this drug are able to cross the phospholipid bilayer because of their lipophilicity.
  6. A woman of reproductive age who has rheumatoid arthritis starts taking a disease-modifying agent known to cause neural tube defects if taken during pregnancy.Which of the following medications affects the cell cycle in the same way as the agent this woman is taking?
  7. Digoxin toxicities
    • Digoxin toxicities include arrhythmias, bradycardia, fatigue, visual disturbances (blurry or yellow vision), and gastrointestinal symptoms (nausea, vomiting, and diarrhea).
    • The antidote for digoxin toxicity is the normalization of K+ and anti-digoxigenin Fab fragments. Lidocaine, cardiac pacers, and magnesium can be used to manage arrhythmias.
  8. A neonate born at 28 weeks' gestation is having difficulty breathing. On physical examination, the neonate's heart rate is 120/min, blood pressure is 100/60 mm Hg, and respiratory rate is 55/min. He has nasal flaring and subcostal retractions.Which of the following components is deficient in this infant?
    • dipalmitoyl phosphatidylcholine, also known as surfactant
    • lecithin:sphingomyelin ratio of the amniotic fluid. If this ratio is >2.0, then the risk of developing neonatal respiratory distress syndrome is significantly decreased
  9. Vasopressin, also known as ADH, binds to the V2 receptor and causes activation of
    adenylyl cyclase via a Gs subunit
  10. intellectual disabilty, spasticity, and an elevated uric acid level. This rare biochemical disorder is characterized clinically by hyperuricemia, excessive production of uric acid, and certain characteristic neurologic features, including self-mutilation, choreoathetosis, spasticity, and mental retardation
    Lesch-Nyhan syndrome, an X-linked recessive disorder caused by a deficiency in hypoxanthine guanine phosphoribosyltransferase that leads to the overproduction of purines and the accumulation of uric acid,
  11. In a nonpathologic state, endothelial cells prevent plaque formation by releasing
    antithrombotic factors such as prostacyclin and nitric oxide.
  12. cyanide MOA
    Cyanide modifies the iron within cytochrome oxidase (cytochrome aa3) in the mitochondria, thereby abnormally interrupting the electron transport chain and halting cellular respiration. Tissues with the highest oxygen demands, such as the heart, brain, and liver, are most significantly affected because cyanide prevents oxygen from binding to cytochrome oxidase and serving as the final electron acceptor in the chain.
  13. physical examination cyanide poisoning
    On physical examination the retinal arteries and veins are bright red due to absent tissue oxygen extraction. Additionally, in some patients there is a smell of bitter almonds on the breath.
  14. 16-year-old boy comes to the clinic for a routine visit. On physical examination, there are several small red papules on the abdomen and scrotum, as well as hyperkeratosis. Review of systems is notable for intermittent paresthesias in the digits bilaterally and heat intoleranc
    Fabry's disease is an X-linked recessive disease caused by a deficiency of the enzyme α-galactosidase A, which results in the accumulation of ceramide trihexoside.
  15. glucose-6-phosphate dehydrogenase deficiency.Which compound builds up because of this deficiency?
    Oxidized glutathione, the build-up of oxidants, which damages hemoglobin as well as enzymes.
  16. Fanconi's anemia,
    This patient has Fanconi's anemia, an autosomal recessive disorder that makes cells more susceptible to chromosomal breakage in response to DNA cross-linking agents. Over 85% of cases are diagnosed between the ages 4 and 15. Patients commonly present with thrombocytopenia or leukopenia, which gradually progresses to pancytopenia and eventually to bone marrow failure. Bone marrow biopsy will show fatty infiltration. In this patient, early fatigue, mucosal bleeding, and recurrent infections are secondary to pancytopenia caused by progressive marrow failure. Two-thirds of patients with Fanconi’s anemia show some form of congenital abnormality, especially thumb abnormalities, hypogonadism, and microcephaly.Patients can be treated with corticosteroids or growth factors in the short term, but bone marrow transplant is needed to address the pancytopenia and its sequelae.Be familiar with the anemia syndromes shown in the table, which may occur in children.
  17. Rotenone
    Rotenone competitively inhibits reduced nicotinamide adenine dinucleotide dehydrogenase (NADH). As a result, the Michaelis-Menten constant increases because rotenone competes with NADH at the enzymatic active site. However, the maximum reaction rate for a given concentration of enzyme does not change, because it can eventually be achieved by increasing the amount of substrate (ie, NADH) available to the enzymes.
  18. things that cause a right shift in the oxygen-hemoglobin dissociation curve
    include increased temperature, increased 2,3-diphosphoglycerate (2,3-DPG), and increased metabolic demands, for example, exercise. During exercise, lactic acid builds up in tissues and causes a metabolic acidosis that shifts the curve in the same way as a respiratory acidosis would, .