Exam 2 Practice Quiz Flashcards
When fatty acids with odd numbers of carbon atoms are oxidized in the β-oxidation pathway the final product is 1 mole of acetyl-CoA and 1 mole of the 3-carbon molecule, propionyl-CoA. In order to use the propionyl carbons, the molecule is carboxylated and converted ultimately to succinyl-CoA and fed into the TCA cycle.
Which of the following represents the vitamin cofactor required in one of the steps of this conversion?
- riboflavin (B2)
- pantothenic acid (B5)
- thiamine (B1)
- cobalamin (B12)
- pyridoxine (B6)
cobalamin (B12)
The urea cycle disorders (UCD) result from defects in the metabolism of the extra nitrogen produced by the breakdown of protein and other nitrogen containing molecules. Infants with a urea cycle disorder often initially appear normal but rapidly develop cerebral edema and the related signs of lethargy; anorexia; hyperventilation or hypoventilation; hypothermia; seizures; neurologic posturing; and coma.
In milder (or partial) urea cycle enzyme deficiencies, ammonia accumulation may be triggered by illness or stress at almost any time of life, resulting in multiple mild elevations of plasma ammonia concentration.
In patients with partial enzyme deficiencies, the first recognized clinical episode may be delayed for months or years.
The mainstays of treatment are 1) reducing plasma ammonia concentration, 2) pharmacologic management to allow alternative pathway excretion of excess nitrogen, 3) reducing the amount of nitrogen in the diet, 4) reducing catabolism through the introduction of calories supplied by carbohydrates and fat, and 5) reducing the risk of neurologic damage.
Which statement is false?
- Urinary orotic acid is significantly elevated in Ornithine transcarbamylase deficiency.
- Carbamyl phosphate synthase I is rendered inactive in the absence of N-acetyl glutamate that is produced by N-acetyl glutamate synthetase.
- Urinary orotic acid is significantly elevated in Carbamyl phosphate synthase I deficiency.
- Blocking the production of ammonia is accomplished by the intravenous administration of a combination of the nitrogen scavenger drugs sodium phenylacetate and sodium benzoate.
Urinary orotic acid is significantly elevated in Carbamyl phosphate synthase I deficiency.
A patient has a deficiency of the enzyme that catalyzes synthesis of N-acetylglutamic acid.
Which of the following would be a consequence of this deficiency in the patient?
- Increased glucose in the blood
- Increased fatty acids in the blood
- Decreased excretion of uric acid
- Increased amino acids in the blood
- Decreased digestion of dietary protein
Increased amino acids in the blood
Children with urea cycle disorders present with elevated serum ammonia and consequent neurologic symptoms including altered respiration, lethargy, and coma. Several amino acids are intermediates of the urea cycle, having side ammonia groups that join with free carbon dioxide (CO2) and ammonia to produce net excretion of ammonia as urea (NH2CONH2).
Which of the following amino acids has a nitrogen in its side chain and is an intermediate of the urea cycle?
- Methionine
- Phenylalanine
- Glutamate
- Arginine
- Aspartate
Arginine
Which is correct. Carbamoyl phosphate synthetase I:
- is a flavoprotein.
- is unresponsive to changes in arginine.
- requires ATP as an allosteric effector.
- is controlled primarily by feedback inhibition.
- requires N-acetyl glutamate as an allosteric effector.
requires N-acetyl glutamate as an allosteric effector
A comatose infant is brought to the ER. In the course of the examination, plasma ammonia was found to be elevated 20-fold over normal values. Urine orotic acid and uracil were both greater than normal.
A defect of which of the following enzymes is the most likely diagnosis?
- Carbamoyl phosphate synthetase II (glutamine)
- Carbamoyl phosphate synthetase I (ammonia)
- Ornithine transcarbamoylase
- Arginase
- Argininosuccinate lyase
Ornithine transcarbamoylase
Inherited deficiency of the enzyme methylmalonyl-CoA (MMA-CoA) mutase causes serum and urine accumulation of methylmalonic acid. Recognition that pernicious anemia (due to deficiency of vitamin B12) can involve accumulation of methylmalonic acid led to successful treatment of some patients with MMA-CoA mutase deficiency using excess B12. Studies of purified MMA- CoA mutase enzyme from normal individuals then showed enhanced mutase activity when B12 was added to the reaction mixture.
These facts are best reconciled by which of the following roles for Vitamin B12?
- Feedback inhibitor of MMA-CoA mutase enzyme
- Competitive inhibitor of MMA-CoA mutase enzyme
- Precursor for methylmalonic acid synthesis
- Covalently attached group for the enzyme methylmalonic acid-CoA mutase
- Cofactor for the MMA- CoA mutase enzyme
Cofactor for the MMA- CoA mutase enzyme
A full-term female infant failed to gain weight and showed metabolic acidosis in the neonatal period. A physical examination at 6 months showed failure to thrive, hypotonia, small muscle mass, severe head lag, and a persistent acidosis (pH 7.0–7.2). Blood lactate, pyruvate, and alanine were greatly elevated.
Which of the following enzymes is most likely deficient in this patient?
- Pyruvate dehydrogenase
- Alanine aminotransferase
- Pyruvate kinase
- Phosphoenolpyruvate carboxykinase
Pyruvate dehydrogenase
A 3-month-old male infant developed seizures and progressively worsened, showing hypotonia, psychomotor retardation, and poor head control. He had lactic acidosis and an elevated plasma pyruvate level, both of which were more than 7 times the normal amount. Pyruvate carboxylase activity was measured using extracts of fibroblasts and was found to be less than 1% of the normal level.
Oral administration of which of the following amino acids would you recommend as the best therapy for this patient?
- Aspartate
- Serine
- Alanine
- Lysine
- Leucine
Aspartate
A 3-month-old boy presents with elevated levels of phenylalanine, para-hydroxyphenylpyruvate, and phenylpyruvate in the serum. His skin color is pale. Your differential diagnosis is PKU.
Which of the following would be consistent in such a case?
- Elevated levels of pyridoxal phosphate in the serum
- Urine in the boy’s diaper smells like fresh maple syrup
- Phenylalanine hydroxylase activity is only 2% of normal
- Deficiency in vitamin B12(cobalamin)
- Elevated levels of homogentisic acid in the serum
Phenylalanine hydroxylase activity is only 2% of normal
A 1-year-old girl presents at your clinic the day after you saw the 3-month-old boy. The symptoms are the same so you order a test on phenylalanine hydroxylase to confirm your diagnosis of phenylketonuria. To your surprise, the phenylalanine hydroxylase activity is well within the normal range.
Which of the following might you check next to support your diagnosis?
- Homogentisic acid oxidase
- Tyrosine: α-ketoglutarate transaminase
- Dihydropteridine reductase (regeneration of tetrahydrobiopterin)
- Tyrosinase
Dihydropteridine reductase (regeneration of tetrahydrobiopterin)
A 35-year-old woman is noted to have a hemoglobin level of 9 g/dL (normal range: 12-14 g/dL). The red cell size is enlarged.
Which of the following tests would best help distinguish between a folate and vitamin B12 deficiency?
- Blood level of cystathionine
- Activity of methionine synthase
- Blood level of methylmalonate
- Blood level of homocysteine
- Blood level of methionine
Blood level of methylmalonate
A 24-year-old woman suffering from a severe head cold had a very poor appetite and had not eaten more than 300 calories per day for the last 3 days. By the third day, which of the following enzymes is playing a key role in the synthesis of her plasma glucose?
- Pyruvate dehydrogenase
- Propionyl-CoA carboxylase
- Glycogen phosphorylase
- Malic enzyme
Propionyl-CoA carboxylase
As a result of biochemical and genetic testing, a 9-month-old boy with a history of neurodevelopmental delay, hypotonia, and several hospitalizations for severe lactic acidosis was diagnosed with an inherited disorder in energy metabolism.
Fasting hypoglycemia was not noted during these hospitalizations. Following the diagnosis, his pediatric specialist prescribed a very low-carbohydrate, high fat diet, and the boy’s clinical course showed some improvement.
Which of the following enzymes or proteins is most likely deficient in this patient?
- Fumarase
- Pyruvate dehydrogenase
- Pyruvate carboxylase
- Glucose 6-phosphatase
Pyruvate dehydrogenase
A newborn is in the neonatal intensive care unit. He is hyperventilating and lethargic, refuses oral nutrition and has had several seizures. Serum analysis reveals the following.
Ammonia
Patient (Unit µM) 4,000
Normal (Unit µM) 50
Citrulline
Patient (Unit µM) 3
Normal (Unit µM) 9-38
Ornithine
Patient (Unit µM) 900
Normal (Unit µM) 20-130
Measurement of which of the following metabolites in the serum or urine would be most helpful for determining the biochemical deficiency that is causing this patient’s illness?
- Orotic acid in the urine
- Urea in the serum
- Uric acid in the serum
- Ammonia in the urine
- Glutamine in the serum
Orotic acid in the urine
Valine and isoleucine give rise to propionyl CoA, a precursor of succinyl CoA. A disease related to a defect in this conversion is methylmalonic aciduria. Some patients respond to megadoses of vitamin B12.
Which of the following statements about the conversion of propionyl CoA to succinyl CoA is/are correct?
- The same pathway of propionyl CoA to succinyl CoA is part of the metabolism of odd-chain fatty acids.
- The first step in the conversion is a biotin-dependent carboxylation.
- Some methylmalonic aciduria patients respond to B12 because the defect in the mutase converting malonyl CoA to succinyl CoA is poor binding of the cofactor.
- all of these choices
All of the above
A 5-year-old girl with moderate mental retardation is brought to the physician by her mother who is concerned that her daughter has been having difficulty with her vision for weeks. Physical examination shows a fair complexion and malar erythema. Ophthalmologic examination shows dislocated lenses bilaterally. She has long, slender hands and fingers. Blood tests reveal her cystathionine concentration is below normal.
This patient is most likely to have an increased urine concentration of which of the following amino acids?
Group of answer choices
- cysteine
- methionine
- leucine
- arginine
- alanine
methionine
A newborn at age 36 hours is showing signs of cerebral edema and becoming irritable, lethargic, and hypothermic. Respiratory alkalosis (increased pH, decreased CO2), increased ammonia level, and decreased blood urea nitrogen level were found. An amino acid screen revealed that argininosuccinate was increased more than 60-fold over baseline, and citrulline was increased 4-fold. Glutamine was elevated, and arginine was decreased relative to normal.
Based on the findings, which enzyme of the urea cycle is most likely to be deficient in this patient?
- Arginase
- Argininosuccinate synthetase
- Argininosuccinate lyase
- Carbamoyl phosphate synthetase I
- Ornithine transcarbamoylase
Argininosuccinate lyase
A 6-day-old newborn, who is being breast-fed, is brought to the ER because he is unresponsive. He has been vomiting and is lethargic for the past 2 days. Examination shows an obtunded infant with hypertonia and muscle rigidity. A peculiar odor of burnt sugar is noted in his diaper.
The plasma concentration of which of the following amino acids is most likely to be increased in this patient?
- homocysteine
- leucine
- phenylalanine
- tyrosine
- cysteine
Leucine
A 22-year-old man comes to the physician 1 week after an episode of severe right flank pain that resolved with the passing of a renal calculus. His 25-year-old brother had similar symptoms 1 year ago.
This patient most likely has an increased urine concentration of which of the following amino acids?
- argininosuccinate and citrulline
- methionine and homocysteine
- lysine and cystine
- phenylalanine and tyrosine
- glycine and alanine
lysine and cystine
An 11-month-old boy is brought to the physician because of lethargy and irritability for the past 3 days, since a diagnosis of a middle ear infection. The physician prescribed an antibiotic to treat the ear infection. Laboratory studies show metabolic acidosis and an increased plasma valine concentration.
Which of the following amino acid concentrations are most likely to be increased in this patient’s blood if he has maple syrup urine disease?
- phenylalanine and tyrosine
- leucine and isoleucine
- asparagine and glutamine
- homocysteine and cysteine
- arginine and lysine
leucine and isoleucine
A well, 2-year-old girl contracted a viral illness at day care with vomiting, diarrhea, and progressive lethargy. She presents to the clinic with disorientation, a barely rousable sensorium, cracked lips, sunken eyes, lack of tears, flaccid skin with “tenting,” weak pulse with low blood pressure, and increased deep tendon reflexes. Laboratory tests show low blood glucose, normal electrolytes, elevated liver enzymes, and (on chest X-ray) a dilated heart. Urinalysis reveals no infection and no ketones.
The child is hospitalized and stabilized with 10% glucose infusion. Admission laboratories show elevated medium-chain fatty acylcarnitines in blood and 6–8 carbon dicarboxylic acids in the urine.
Which of the following abnormalities is the most likely diagnosis in this child?
- Carnitine deficiency
- Defect of medium-chain coenzyme A dehydrogenase
- Defect of medium-chain fatty acyl synthetase
- Mitochondrial defect in fatty acid transport
- Mitochondrial defect in the electron transport chain
Defect of medium-chain coenzyme A dehydrogenase
In liver, which of the following inhibitory effects is the key regulatory event that ensures newly synthesized palmitoyl-CoA is not immediately oxidized?
- Acyl-CoA synthetase by malonyl-CoA.
- Carnitine–acylcarnitine translocase (CAT) by palmitoyl-CoA.
- Carnitine–palmitoyl transferase-I (CPT-I) by malonyl-CoA.
- CPT-I by palmitoylcarnitine.
- Carnitine–palmitoyl transferase-II (CPT-II) by acetyl-CoA.
Carnitine–palmitoyl transferase-I (CPT-I) by malonyl-CoA.
A prime diagnostic indicator for the first presentation of diabetes mellitus type 1 is the presence of ketonuria and severe acidosis.
Which of the following are “ketone bodies” that would be elevated in serum and urine from a child with diabetic ketoacidosis?
- Acetone and ethanol
- Fumarate and succinate
- Oxaloacetate and pyruvate
- Pyruvate and lactate
- β-Hydroxybutyrate and acetoacetate
β-Hydroxybutyrate and acetoacetate
Metabolism of aromatic amino acids involves the following pathways. Which choice matches the conditions with the correct enzymatic deficiencies (numbered 1 through 5 in the table shown below)?
Row 3
Several lipases are involved in the storage and retrieval of fat in adipocytes. They include capillary lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL). How would these lipases respond to a heavy but balanced meal?
- Row 1
- Row 2
- Row 3
- Row 4
- Row 5
Row 2
Intestinal epithelial cells possess 2 transport mechanisms to move glucose across the plasma membrane, a facilitated glucose carrier (GLUT2) as well as a sodium-dependent secondary active transporter (SGLT1).
Which of the following attributes distinguishes these 2 transport modalities with respect to net glucose transport?
- GLUT2 directly depends on ATP hydrolysis
- GLUT2 is sensitive to competitive substrate inhibition
- SGLT1 can transport glucose from a region of low to a region of high concentration
- SGLT1 is saturable
SGLT1 can transport glucose from a region of low to a region of high concentration
The small intestine is the major site of dietary glucose uptake into the body, and SGLT1 plays a pivotal role in luminal glucose uptake.
Which statement is false?
- Glucose absorption requires active Na+ removal by the Na+ /K+ -ATPase
- Na+ /K+ -ATPase generates the electrochemical driving force for glucose entry via Na+ -driven sodium–glucose cotransport
- Glucose exits the cells following its concentration gradient primarily via GLUT2 and enters the bloodstream
- Glucose exits via a unidirectional glucose transporter.
Glucose exits via a unidirectional glucose transporter.
Most reported cases of pyruvate dehydrogenase (PDH) dysfunction to date have been shown to be due to the inactivation of the PDH E1 alpha subunit, which contains a sulfhydryl enzyme vulnerable to damage from reactive oxygen species.
Which statement is false?
- Ketones bypass the PDH complex to provide an alternative substrate for the TCA cycle and so mitochondrial function can be restored even under such conditions.
- PDH dysfunction causes an increase in pyruvate and lactate levels.
- PDH dysfunction causes an increase in the activity of the Na, K-ATPase in neurons.
- ATP production is decreased due to inability to convert pyruvate into Acetyl-CoA.
PDH dysfunction causes an increase in the activity of the Na, K-ATPase in neurons.
Digoxin is the cardiac glycoside of the digitalis group. It works directly on myocardium and smooth muscle vascular and indirectly increases the force of myocardial contraction while slows heart rate.
- The binding of digoxin to Na+/ K+-ATPase in the cell membrane and its inhibition results in an increase in intracellular sodium content.
- Digoxin leads to the rise in intracellular calcium content.
- Calcium channel blockers can be prescribed with digoxin.
- Digoxin toxicity can be increased if administered with a potassium-lowering drugs
Calcium channel blockers can be prescribed with digoxin
Approximately 70% of all breast cancers are dependent for their growth on estrogen and on a functional estrogen receptor α (ERα).
Hence, ER-positive breast cancer is usually treated with hormone reduction or anti-estrogens. Tamoxifen is an example of anti-estrogen.
Based on the following figure, which is false about tamoxifen resistant cells?
- Tamoxifen makes ERα inactive by occupying the estrogen binding site.
- Activation of protein kinase A (PKA) prevents tamoxifen-mediated inhibition of ERα activation.
- A G protein activates adenylate cyclase that generates cAMP.
- cAMP binding to the catalytic subunit of the PKA complex releases the inhibitory subunit of the tetrameric PKA complex.
Tamoxifen makes ERα inactive by occupying the estrogen binding site.
