GENERAL PRACTITIONER EXAM KIT-74

GENERAL PRACTITIONER EXAM

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Question 1 of 36

1. Question

1 points

A 22 year old woman is doing intense aerobic exercise. Aerobic glycolysis is being used for the source of energy for the muscle activity. The carbons derived from glucose enter the krebs cycle in which one of the following form?

Acetyl-CoA
Citrate
Oxaloacetate
Pyruvate

Correct

Incorrect

Explanation:

In aerobic glycolysis, glucose is degraded to pyruvate, which is then converted to acetyl-CoA, the form in which it actually enters the citric acid cycle. Two acetyl-CoAs, each containing two of the glucose´s carbons, are produced from each glucose molecule. In addition, a total of two carbons from glucose are released as CO₂ when each of the two pyruvates are converted to acetyl-CoA. Citrate is the product formed in the citric acid cycle when acetyl CoA condenses with oxaloacetate. Oxaloacetate is the citric acid cycle intermediate that condenses with acetyl-CoA to form citrate. Two pyruvates are produced from degradation of glucose. These are then converted to the two acetyl-CoAs that enter the citric acid cycle. Succinate is another citric acid cycle inter-mediate that forms when coenzyme A is removed from succinyl-CoA.

Question 2 of 36

2. Question

1 points

The polymerase chain reaction (PCR) is used to amplify small amounts of deoxyribonucleic acid (DNA) for further analysis. First the DNA double helix must be split into two strands.

Alkali solution
Centrifugation
DNA polymerase
Heating to nearly 100°C

Correct

Incorrect

Explanation:

To the small sample of DNA are added two oligonucleotides with sequences that have affinity for both ends of the area of DNA that is being studied. A thermostable DNA polymerase is also added. At 94°C DNA literally melts into two single strands and with cooling the oligonucleotides bind to the areas surrounding the particular area of DNA that is being analysed. These act as primers for the DNA polymerase and a new double helix of DNA is formed. The cycle is repeated doubling the amount of DNA each time.

Question 3 of 36

3. Question
1 points
Phosphorylation of protein tyrosine residues is associated with:
- Protein catabolism
- Cell signaling pathways
- Alzheimer´s disease
- Protein synthesis
Correct

Incorrect

Explanation:

Phosphorylation of specific tyrosine residues of components of cell signalling pathways is often a key event in the activation of the pathway.
Question 4 of 36

4. Question
1 points
Proteins known as cyclins:
- Levels rise unanimously
- Levels fall unanimously
- Regulate the cycling of receptors between the cell surface and the cytoplasm
- Are differentially expressed throughout the cell cycle
Correct

Incorrect

Explanation:

Cyclins are key regulators of the cell cycle; different cyclins are expressed at different stages of the cell cycle.

Question 5 of 36

5. Question

1 points

Where does RNA splicing occur?

Smooth endoplasmic reticulum
Rough endoplasmic reticulum
Mitochondria
Nucleus

The D forms of amino acids are actively transported in the enterocyte by sodium dependent processes. Dietary proteins are initially degraded in the stomach by acid and pepsins (A). Pancreatic proteases complete the process, resulting in oligopeptides, dipeptides, and amino acids. Dipeptides are absorbed more rapidly than amino acids (B). Amino acids are rapidly absorbed in the duodenum and jejunum, but slowly in the ileum (C). Most naturally occurring amino acids are the L amino acids. Sodium ions are necessary for absorption of these amino acids (D).

Question 9 of 36

9. Question
1 points
Gaucher´s disease syndrome represents which type of inborn error of metabolism?
- Lipid storage disease
- Disorder of lipoprotein metabolism
- Disorder of amino leukodystrophy acid metabolism
- Disorder in purine and pyrimidine metabolism
Correct

Incorrect

Explanation:

Gaucher´s disease is a lipid storage disease in which there is a deficiency in beta glucosidase.

Question 10 of 36

10. Question

1 points

Pyridoxine syndrome represents which one of the following types of inborn error of metabolism?

Lipid storage disease
Disorder of lipoprotein metabolism
Glycogen storage disease
Disorder of amino leukodystrophy acid metabolism

Correct

Incorrect

Explanation:

Pyridoxine dependency is an autosomal recessive disorder of amino acid metabolism in which there is a deficiency of glutamic acid decarboxylase activity in the brain, resulting in reduced synthesis of GABA.

Question 11 of 36

11. Question

1 points

Which one of the following is a clinical manifestation of Vitamin B12 deficiency?

Dementia.
Anemia.
Night blindness.
Osteoporosis.

Correct

Incorrect

Explanation:

Cyanocobalamin deficiency causes a megaloblastic anemia (large mean corpuscular volume of the RBC) and a peripheral neuropathy. The other vitamin deficiencies do not commonly present with anemia.

Question 12 of 36

12. Question
1 points
A 66 year old woman on high dose antibiotics in the medical intensive care unit is found to be deficient in a vitamin that is synthesized by intestinal bacteria. The most likely vitamin is
- Vitamin B6
- Vitamin C
- Vitamin D
- Vitamin K
Correct

Incorrect

Explanation:

Vitamin K is synthesized by intestinal bacteria.

Question 13 of 36

13. Question

1 points

Vitamin E is NOT characterized by which of the following?

Deficiency results from fat malabsorption syndromes.
Abetalipoproteinemia predisposes to deficiency
Alpha tocopherol is the most biologically active form.
It functions as a cofactor.

Correct

Incorrect

Explanation:

Of the eight naturally occurring tocopherols possessing vitamin E activity, alpha tocopherol is the most widely distributed and biologically active form. Vitamin E is fat soluble. The vitamin enters the blood stream via lymph, initially associated with chylomicrons and then with plasma beta lipoproteins. Deficiency results from fat malabsorption syndromes, abetalipoproteinemia, and chronic cholestatic liver disease. Vitamin E functions as an antioxidant and free radical scavenger.

Question 14 of 36

14. Question

1 points

What acid base disturbance is most likely caused by salicylate toxicity?

Metabolic acidosis
Respiratory alkalosis
Respiratory acidosis
Both (B) and (C).

Correct

Incorrect

Explanation:

Salicylates cause both a respiratory alkalosis (by direct stimulation of the CNS respiratory center, causing hyperventilation) and an anion gap metabolic acidosis. They do not typically cause a metabolic alkalosis or respiratory acidosis.

Question 15 of 36

15. Question

1 points

All of the following are functions of apolipoproteins, EXCEPT

Serving as ligands for cellular lipoprotein receptors.
Acting as cofactors for plasma enzymes.
Providing a surface monolayer to enhance particle solubilization.
Serving as ligands for plasma enzymes.

Correct

Incorrect

Explanation:

Apolipoproteins reside on the surface of lipoproteins. Polar lipids, in conjunction with amphipathic apolipoproteins, form a surface monolayer to assist in solubilization of particles. The apolipoproteins provide structural stability to lipoproteins, serve as ligands for cellular lipoprotein receptors, and act as cofactors for plasma enzymes. Some of these apolipoproteius serve in two or more of these capacities. They do not serve as ligands for plasma enzymes.

Question 16 of 36

16. Question
1 points
A 24-year-old woman has a fusiform swelling of the Achilles tendon which shows foam cells among the collagen fibers on biopsy. She has joint pains for several years similar to her parents who also had xanthomas, but their first symptoms occurred in middle age. Which of the following is most likely elevated in the blood of this woman?
- Chylomicron-remnants
- Chylomicrons
- High density lipoproteins (HDL)
- Low density lipoproteins (LDL)
Correct

Incorrect

Explanation:

Deposition of xanthomas around the Achilles tendon is characteristic of familial type IIa hyperlipidemia, an autosomal dominant deficiency of the LDL receptor. The resultant reduced rate of LDL clearance leads to elevated LDL levels and hypercholesterolemia. For some poorly understood reason, arthritic pain in various joints, often prior to any appearance of xanthomas, is a characteristic of familial type IIa hyperlipidemia manifestation. Although Achilles tendonitis with associated xanthomas is common, other tendons may be involved. Symptoms in the heterozygous patient usually do not occur until the third or fourth decade, but homozygotes are affected much earlier, often in childhood. The patient was most likely treated with an HMG CoA reductase inhibitor such as simvastatin. Her condition carries a strong risk for cardiovascular disease. Although xanthomas are common in other familial hyperlipemias, such as type III and hepatic lipase deficiency, these are not associated with Achilles tendonitis.
Chylomicrons remnants accumulate in familial type III hyperlipidemia (also known as familial dysbetalipoproteinemia) due to a lack of functional apolipoprotein E. Chylomicronemia is associated with familial lipoprotein lipase deficiency (type I hyperlipoproteinemia). This rare autosomal recessive disease inhibits the clearance of the chylomicrons. HDLs are the “good” lipoproteins; they have a protective effect against atherosclerosis. Their role is to take up free cholesterol from cell surfaces and circulating apolipoproteins. There is a tendency of VLDL to be increased in several of the hyperlipoproteinemias, none of which produce the symptoms described. Familial type IV hyperlipidemia is probably the most significant, as it is associated with the hyperinsulinemia commonly observed in insulin-resistant, type 2 diabetes. The resultant concomitant increase in cholesterol and decrease in HDL lead to vascular disease, a critically important part of the insulin resistance syndrome.
Question 17 of 36

17. Question
1 points
A genetics researcher is trying to identify a potential gene from a gene signature/motif that encodes a seven-helix transmembrane domain. Which of the following is an example of a glycosylated, integral membrane protein with seven transmembrane segments?
- Na+/K+ATPase
- Cystic fibrosis transmembrane conductance regulator channel
- Glucose transporter
- Beta-adrenergic receptor for epinephrine
Correct

Incorrect

Explanation:

This question requires that you recognize the family of receptors that interact with G proteins to initiate a signal transduction cascade. These receptors are all glycosylated integral membrane proteins that have seven transmembrane segments. Beta-adrenergic receptors for epinephrine are an example.
Adenylate cyclase is an intracellular effector protein involved in signal transduction. It is not an integral membrane protein. The cystic fibrosis transmembrane conductance regulator channel is a cyclic AMP-activated chloride channel. Glucose transporters are integral membrane proteins with 12 membrane-spanning domains. Na⁺/K⁺ ATPase pumps sodium into and potassium out of the cell. It provides energy for active transport by hydrolyzing ATP.
Question 18 of 36

18. Question
1 points
A 30-year-old man has been fasting for several days.His blood glucose level is now about 60% of its normal value, but he does not feel lightheaded because his brain has reduced its need for serum glucose by using which of the following substances as an alternate energy source?
- Beta-carotene
- Acetyl Co-A
- C-reactive protein
- Beta-hydroxybutyrate
Correct

Incorrect

Explanation:

Ketone bodies, which include acetoacetate, beta-hydroxybutyrate, and acetone, are produced by the liver in the fasting state by beta-oxidation of fatty acids. They are then released into the blood stream, where they can be used as alternative energy sources for other organs, such as muscle, kidney, and brain. The brain specifically still requires a small amount of circulating glucose to function, but the amount required is reduced when ketone bodies are available.
Apoprotein B is one of the proteins that hold lipoproteins together.
Beta-carotene is a vitamin with antioxidant properties.
C-reactive protein is a serum protein produced by the liver that rises during infections and in inflammatory states. Acetyl-CoA is a product of beta oxidation and other metabolic pathways.

NOTE
Ketone bodies can be used for energy. Ketone bodies are transported from the liver to other tissues, where acetoacetate and beta-hydroxybutyrate can be reconverted to acetyl-CoA to produce energy, via the citric acid cycle.
The heart preferentially utilizes fatty acids for energy under normal physiologic conditions. However, under ketotic conditions, the heart can effectively utilize ketone bodies for energy.
The brain gets a portion of its energy from ketone bodies when glucose is less available (e.g., during fasting, strenuous exercise, low carbohydrate, ketogenic diet and in neonates). In the event of low blood glucose, most other tissues have additional energy sources besides ketone bodies (such as fatty acids), but the brain does not. After the diet has been changed to lower blood glucose for 3 days, the brain gets 25% of its energy from ketone bodies. After about 4 days, this goes up to 70% (during the initial stages the brain does not burn ketones, since they are an important substrate for lipid synthesis in the brain). Furthermore, ketones produced from omega-3 fatty acids may reduce cognitive deterioration in old age.
Question 19 of 36

19. Question
1 points
Ciprofloxacin fails to treat fever, abdominal cramps, and severe watery diarrhea in a 60-year-old woman. She has a missense mutation that conferred resistance to ciprofloxacin. Mutation is most likely in the gene encoding an enzyme essential for which of the following functions?
- DNA replication
- Folate synthesis
- mRNA translocation on a ribosome
- Translation
Correct

Incorrect

Explanation:

Ciprofloxacin, a quinolone derivative, inhibits DNA gyrase (prokaryotic topoisomerase II) essential for DNA replication. A mutation in the gene for DNA gyrase has made the enzyme insensitive to the effects of ciprofloxacin.
Folate synthesis is inhibited by sulfamethoxazole, not ciprofloxacin.
mRNA translocation on a ribosome is inhibited by erythromycin, not ciprofloxacin.
Peptide bond formation (Translation) is inhibited by chloramphenicol, not ciprofloxacin. Reduction of folate to tetrahydrofolate is inhibited by trimethoprim, not ciprofloxacin.
Transcription is not related to ciprofloxacin.
Question 20 of 36

20. Question
1 points
A patient has an enlarged liver and kidneys, gout, and xanthomas. Studies show that he has a genetic deficiency of glucose 6-phosphatase. Additional studies would most likely show which of the following sets of laboratory results? s
- Serum Serum Serum glucose lactate Pyruvate High High High
- Serum Serum Serum glucose lactate Pyruvate High High Low
- Serum Serum Serum glucose lactate Pyruvate High Low Low
- Serum Serum Serum glucose lactate Pyruvate Low High High
Correct

Incorrect

Explanation:

This is Von Gierke disease, one of the glycogen storage diseases. The defect in glucose-6-phosphatase prevents release of glucose from glycogen across the liver cell membrane. The glucose-6-phosphate trapped in the liver cell is degraded to lactate and pyruvate, which are then released into the serum.
Question 21 of 36

21. Question
1 points
When a cloned DNA fragment is used as a probe, a restriction fragment length polymorphism (RFLP) is revealed in the region adjacent to the centromere of chromosome 21. Four haplotypes exist: A, B, C, and D. An AB woman and a CD man have an ACC child with trisomy 21. Nondisjunction traces to:
- Paternal meiosis II
- The Paternal meiosis I
- The child during the first mitotic division
- Maternal meiosis I
Correct

Incorrect

Explanation:

The RFLP detects a region near the centromere of chromosome 21. The region around the centromere exhibits a phenomenon called crossover suppression. Since genetic exchange cannot happen in this area, the probe is a reliable marker for the individual chromosomes. During meiosis II, sister chromatids, which are two identical copies of the same chromosome, should separate. If a nondisjunction event occurs in this division, two copies of the same chromosome are passed to the progeny In this case, both parents are heterozygous for the RFLP. The child received an A from the mother and two Cs from the father, leading us to conclude that the problem occurred in the father during meiosis II.
If a nondisjunction event of chromosome 21 occurs early in development, the result is a child who is a mosaic for trisomy 21. This accounts for approximately 1% of children with trisomy 21. Since some of their cells are normal, these individuals show only a mild expression of the trisomy 21 phenotype.
During meiosis I, homologues that carry similar, but not identical, information separate. If a failure occurred in this division, we would expect the man to pass CD, and the woman to pass A or B, producing a child that was ACD or BCD.
If an AB woman had a failure in meiosis I, an AB gamete would be produced. When fertilized by the man´s C or D sperm, a child that was ABC or ABD would result.
If an AB woman´s sister chromatids failed to disjoin during meiosis II, AA or BB gametes would result. When fertilized by the CD male´s sperm, a child that was AAC, AAD, BBC, or BBD would result.
Question 22 of 36

22. Question
1 points
A 28-year-old woman and a 25-year-old man present for genetic counseling. Both are white and have one sibling affected with cystic fibrosis. The most appropriate method to assess the risk of transmitting cystic fibrosis to a potential child would be
- Biochemical testing
- Fluorescence in situ hybridization (FISH)
- Karyotype analysis
- Polymerase chain reaction (PCR)
Correct

Incorrect

Explanation:

Cystic fibrosis is an autosomal recessive disease caused by point mutations or small deletions in the gene encoding an integral membrane protein that functions as a chloride transporter. Although many mutations within the gene cause the phenotype, it is not practical or cost-effective to sequence the entire region to screen for a carrier. In the white population, however, the most frequent mutant allele causing cystic fibrosis is due to a small deletion at phenylalanine 508 in exon 10 on chromosome 7. This mutation accounts for greater than 50% of mutant cystic fibrosis alleles in white populations. An amplification of this region using the polymerase chain reaction (PCR) can be done, and the PCR products are sequenced and com-pared against the normal sequence for this region. If comparison reveals the deletion, the donor of that template DNA would be classified as a carrier. If the mutation is not present, the probability that the DNA donor is a carrier of cystic fibrosis is greatly reduced, but still exists. Most diagnostic laboratories will use this method to screen for between 4 and 10 of the most common mutations. Note that if a person belongs to a different ethnic group, PCR must be used to amplify the exons that contain the majority of cystic fibrosis mutations within that particular ethnic group.
Biochemical testing is usually used to detect a defective enzyme or a reduced amount of the normal enzyme. It is more economical than DNA testing for detecting carriers or affected individuals. It is used in the detection of carriers of autosomal recessive diseases, such as Tay-Sachs disease, sickle cell anemia, and the thalassemias.
Fluorescence insitu hybridization (FISH) uses a DNA probe that has been labeled with a fluorescent compound to visualize locations on the chromosomes that have homology to the probe. It can be used to detect microdeletions in a gene of interest.
Karyotype analysis is used to determine whether an individual´s chromosomes are grossly normal in their number and structure. It can be used to detect trisomies, monosomies, and. translocations, as well as large inversions and deletions.
Western blot analysis is a technique commonly used to detect the presence of antibody against specific proteins in serum. It is primarily used as a confirmatory test for HIV infection.
Question 23 of 36

23. Question
1 points
A 2-year-old boy has cognitive and motor skill deterioration, dysarthria and dysphagia along ataxia. Cherry red spot is seen. A biochemical defect involving hexosaminidase A is present. The patient´s condition would be most appropriately categorized as belonging to which of the following general classes of defects?
- Aminoacidopathy
- Gangliosidosis
- Lipid metabolism
- Mucopolysaccharidosis
Correct

Incorrect
Explanation:
Deficiencies of the enzyme hexosaminidase A result in Tay-Sachs disease, an autosomalrecessive disorder most commonly seen in Ashkenazi Jews. Tay-Sachs can best be described as a gangliosidosis, since ganglioside GM, accumulates. Tay-Sachs disease is classified into several forms, which are differentiated based on the onset age of neurologicalsymptoms.

Infantile Tay-Sachs disease: At six months after birth; relentless deterioration of mental and physical abilities. Death usually occurs before the age of four.

Juvenile Tay-Sachs disease: Between two and ten years old; cognitive and motor skill deterioration, dysarthria, dysphagia, ataxia, and spasticity; they typically die between five and fifteen years old.

Adult/Late-Onset Tay-Sachs disease: A rare form of Tay-Sachs disease, usually has its first symptoms during the 30s or 40s. It is usually not fatal as it can stop.

An example of an aminoacidopathywould be the autosomal recessive phenylalanine hydroxylase deficiency associated with phenylkeetonuria; Lipid metabolism disorders often involve a defect at the LDL receptor. These types of disorders can be seen in patients with the autosomal dominant disorder familial hypercholesterolemia.
An example of a mucopolysaccharidosis is an X-linked recessive deficiency of iduronate sulfatase, or Hunter syndrome. Acute intermittent porphyria is an autosomal dominant disorder involving a biochemical defect of porphobilinogen deaminase.
Question 24 of 36

24. Question
1 points
A 4-year-old boy has gastroenteritis for three days, followed by a brief generalized seizure that left him semicomatose. The blood glucose level at admission is 18 mg/dL (0.10 mM) and urine is negative for glucose and ketones, but positive for a variety of organic dicarboxylic acids. IV glucose improves his condition with-in 10 minutes. Following diagnosis of an enzyme deficiency, his parents are cautioned to make sure he eats frequently. Which of the following is the most likely diagnosis?
- Glucose-6-phosphatase deficiency
- Hepatic glycogen phosphorylase deficiency
- Medium chain acyl CoA dehydrogenase deficiency
- (Mitochondria) carbamoyl phosphate synthetase deficiency
Correct

Incorrect

Explanation:

Hypoglycemia with hypoketosis after fasting suggests a block in fatty acid oxidation. Accumulation of organic dicarboxylic acids further indicates a fatty acyl-CoA dehydrogenase deficiency; most commonly this will be a medium chain acyl CoA dehydrogenase (MCAD) deficiency. MCAD deficiency is an autosomal recessive disease expressed with high frequency among people of Northern European descent. Homozygous individuals are unable to break down fatty acids, and so cannot use fat for energy production when glucose supplies are limited. This blockage may also lead to a secondary carnitine deficiency because the accumulated acyl CoA is trans-esterified to produce aryl carnitine. Because carnitine is required to transport fatty acids into mitochondria for oxidation, this also will increase tissue dependence on glucose metabolism. Because ketogenesis also depends on fatty acid catabolism, the brain has no source of ketones to use as an alternative fuel. Whether due to the primary block, the induced carnitine deficiency, or a combination of the two, the net result is acute hypoglycemia whenever glucose is not readily available. Symptoms most commonly appear between two months and two years, but they may be noted as early as two days or as late as six years, and on occasion, asymptomatic parents have first been diagnosed after one of their children have an episode. Generally, symptoms appear after a period of dietary carbohydrate deficiency; presumably, this is what happened in this boy due to his gastroenteritis. It has been estimated that MCAD accounts for about 1% of deaths due to sudden infant death syndrome (SIDS), and about 20% of children with MCAD the after the first episode. The hypoglycemia can occur quickly, and CNS symptoms become marked when venous blood glucose levels drop to about 20 mg/dL (0.11 mM). The mainstay of treatment is to remain well fed on a high carbohydrate diet. Some physicians also prescribe L-carnitine, which is claimed to help maintain blood glucose levels during sickness or other forms of stress.
Glucose 6-phosphatase deficiency is a glycogen storage disease that will also lead to a fasting hypoglycemia, but ketone bodies would accumulate, and there would be no accumulation of organic dicarboxylic acids. Hepatic glycogen phosphorylase deficiencyis a glycogen storage disease that will also lead to a mild fasting hypoglycemia with formation of ketone bodies, but without accumulation of organic dicarboxylic acids. Mitochondria carbamoyl phosphate synthetase deficiency is a urea cycle enzyme deficiency disease that will cause hyperammonemia, not hypoglycemia, and accumulation of organic dicarboxylic acids. Ornithine transcarbamoylase deficiency is also a urea cycle enzyme deficiency disease that will cause hyperammonemia, rather than hypoglycemia, and accumulation of organic dicarboxylic acids.
Question 25 of 36

25. Question
1 points
A 42 year old formerly obese woman presents to the clinician. She was very proud of having lost 80 lb during the previous 2 years, but has now noticed that her “hair is failing out.” According to her she followed a strict, fat free diet. Which vitamin deficiency is the cause of her alopecia?
- A
- C
- D
- E
Correct

Incorrect

Explanation:

Although it is hard to develop a deficiency in oil-soluble vitamins (A, D, E, K) because the liver stores these substances, deficiency states can be seen in chronic malnutrition (specifically chronic fat deprivation) and chronic malabsorption. Vitamin A is necessary for formation of retinal pigments (deficiency can cause night blindness) and for appropriate differentiation of epithelial tissues (including hair follicles, mucous membranes, skin, bone, and adrenal cortex). Vitamin C, which is water soluble rather than oil soluble, is necessary for collagen synthesis. Vitamin D is important in calcium absorption and metabolism. Vitamin E is a lipid antioxidant that is important in the stabilization of cell membranes. Vitamin K is necessary for normal blood coagulation.
Question 26 of 36

26. Question
1 points
A 9 year old girl with mild mental retardation was healthy at birth but presented during the first week of life with vomiting, lethargy, seizures, and hypertonia. Amino acid screen showed elevated levels of leucine, isoleucine, and valine, so the child was put on a special diet restricted in these amino acids. No medical problems were present related to her disease since that time. The enzyme that is most likely deficient in this child is
- Branched chain ketoacid dehydrogenase
- Cystathionine synthase
- Methylmalonyl CoA mutase
- Ornithine transcarbamoylase
Correct

Incorrect

Explanation:

Valine, leucine, and isoleucine are the branched chain amino acids. Deficiency of the branched chain ketoacid dehydrogenase causes maple syrup urine disease, in which branched chain ketoacids build up in blood, urine, and tissues. The urine has the odor of maple syrup and a metabolic acidosis is produced. Early diagnosis is essential to limit an irreversible mental retardation. Treatment consists of a special diet with limited amounts of these amino acids. If untreated, death occurs within a year. Cystathionine synthase converts homocysteine to cystathionine. A deficiency of this enzyme causes a form of homocystinuria (homocystinuria I). Methylmalonyl CoA mutase catalyzes a vitamin B12-requiring step in the conversion of propionate from the amino acids threonine, valine, isoleucine, and methionine, and from odd numbered fatty acids to succinyl-CoA. Note that these are not the same set of amino acids involved in maple syrup urine disease, although the symptoms of the condition are somewhat similar. Deficiency of the methylmalonyl CoA mutase results most commonly in neonatal ketosis and metabolic acidosis with lethargy, vomiting, diarrhea, muscle hypotonia, and if not treated, coma and death. Some cases can be treated by restricting protein and supplementing with extra cobalamin. Ornithine transcarbamoylase deficiency is a urea cycle enzyme deficiency disease associated with hyperammonemia. Propionyl CoA carboxylase catalyzes a reaction analogous to that of acetyl-CoA carboxylase. Both form a malonyl derivative and require biotin as a cofactor. The carboxylation is a step in the conversion of propionate and odd numbered fatty acids to succinyl-CoA.
Question 27 of 36

27. Question
1 points
An initially healthy neonate develops vomiting, diarrhea, abdominal pain, and hypoglycemia when weaning is attempted. Investigations show a generalized metabolic disturbance with lactic acidosis, hyperuricemia, and hyperphosphatemia. Hereditary fructose intolerance is confirmed with an IV fructose tolerance test, and strict dietary restriction of fructose is ordered. Dietary intake of which substance should also be restricted?
- Galactose
- Glucose
- Lactose
- Sucrose
Correct

Incorrect

Explanation:

Several forms of genetic abnormalities of fructose can occur. The mildest, virtually asymptomatic, condition is essential (benign) fructosuria, due to a lack of fructokinase, which phosphorylates fructose. In marked contrast, the genetic abnormality of fructose metabolism described in the question stem is hereditary fructose intolerance (fructosemia), the most severe of these conditions. It is due to a deficiency of the enzyme aldolase B, which is found in liver, small intestine, and kidney. Aldolase B normally cleaves fructose-1-phosphate, and the severe abnormalities seen are related to a disastrous depletion of intracellular phosphate, which is needed for making ATP and other phosphorylated compounds. Hereditary fructose intolerance requires very strict dietary control of fructose, which in practice means that not only fructose (fruit sugar) itself must be controlled, but the much more prevalent sucrose (table sugar) must also be controlled, since it is a disaccharide composed of fructose and glucose. The sugar alcohol sorbitol (an artificial sweetener) is also restricted, since this compound can also be converted to fructose. Galactitol is a sugar alcohol related to galactose, which need not be restricted in this condition. Galactose is a monosaccharide that is metabolized normally in this condition. Metabolic disorders associated with galactose metabolism, analogous to those of fructose, occur because of genetic defects in the kinase enzyme (galactokinase deficiency) and a transfer enzyme (galactose-l-phosphate uridyl transferase deficiency).
Glucose is metabolized normally in this condition. Lactose, a disaccharide composed of galactose and glucose, should be restricted in severe genetic diseases of galactose, as well as in lactose intolerance.
Question 28 of 36

28. Question
1 points
A 74 year old man presents with a several week history of fatigue. Examination shows severe pallor. CNS examination shows poor short term memory and decreased vibration sense in his legs. ECG shows changes consistent with the presence of cardiac ischemia. Hemoglobin level is 4.1 g/dL, with a mean corpuscular volume of 105 µm³, a white cell count of 3100 per mm³, and a platelet count of 55,000 per mm³. The peripheral blood smear shows hypersegmentation of neutrophils, marked anisocytosis, poikilocytosis with some large oval erythrocytes, and basophilic stippling. The metabolic response that is most specific for the vitamin deficiency affecting this patient is
- Decreased blood δ-aminolevulinic acid (ALA)
- Decreased transketolase activity in erythrocytes
- Decreased urinary homocysteine
- Increased urinary methylmalonate (MMA)
Correct

Incorrect

Explanation:

The combination of neurologic symptoms and megaloblastic anemia is characteristic of a vitamin B₁₂ (cyanocobalamin) deficiency, which will also cause an increase in urinary methylmalonate (MMA) due to low activity of methylmalonyl CoA mutase. Megaloblastic anemia is caused by impaired DNA synthesis, which slows cell division, thus decreasing the count for cells with a rapid turnover. In the surviving cells, synthesis of cytoplasmic components proceeds unabated, while cellular division is slowed. Thus, these cells tend to be oversized, misshapen, and have various cytoplasmic inclusions. The direct cause of the decreased rate of DNA synthesis is the unavailability of folate, needed most acutely for conversion of dUMP to dTMP. Therefore, supplementation with folate will cause a rapid reversal of these symptoms. In the case described, there are also symptoms of neuropathy, a characteristic of vitamin B₁₂ deficiency not associated with folate deficiency. In addition to causing neuropathy, a vitamin B₁₂ deficiency will produce a secondary folate deficiency by preventing the regeneration of tetrahydrofolate. Cofactors derived from vitamin B₁₂ carry out only two functions. One is in the conversion of homocysteine to methionine. N⁵-methyltetrahydrofolate is a cosubstrate in this reaction and simultaneously loses its methyl moiety and is converted to tetrahydrofolate. N⁵-methyltetrahydrofolate has no other function, and unless it is converted to a form that can be recycled, it serves as a folate sink, making tetrahydrofolate unavailable for any other reaction. The other reaction requiring a vitamin B₁₂ cofactor is catalyzed by methyl-malonyl CoA mutase, in which methylmalonyl CoA is converted to succinyl CoA. This is the last step in the breakdown of odd carbon fatty acids, and inhibition of this reaction leads to odd carbon fatty acid accumulation in neuronal sheaths and, as a result, neuropathy.
Decreased blood δ-aminolevulinic acid (ALA) would occur with pyridoxine deficiency. Decreased transketolase activity in erythrocytes would occur with thiamine deficiency. Because both cofactors are required to convert homocysteine to methionine, homocysteine levels would increase in the urine of either a folate- or vitamin B₁₂-deficient person. Lactic acidosis would occur in any condition in which lactate accumulates. These could involve many of the reactions in carbohydrate or oxidative metabolism, none of which are relevant to this question.

Question 29 of 36

29. Question

1 points

Contents of a 22 year woman´s regular diet are 125 g carbohydrate, 15 g protein, and 10 g fat daily. Which of the following roughly describes her daily caloric intake?

450 kcal/day
650 kcal/day
850 kcal/day
1050 kcal/day

Correct

Incorrect

Explanation:

You should know that 1 g of either protein or carbohydrate produces about 4 kcal = 4 calories (kcal) of energy, and 1 g of fat produces 9 kcal = 9 calories of energy. The calculation is then straightforward. The calories from carbohydrates are 125 X 4 = 500; from protein are 15 X 4 = 60; and from fat are 10 X 9 = 90. The total is 500 + 60 + 90 = 650 kcal/day.

Question 30 of 36

30. Question
1 points
An 84 year old man presents because of diarrhea and vomiting for the past month. His diet consists of dried cereal and maize; he never eats mills or eggs. Examination shows sharply demarcated plaques on his hands, feet, and around his neck. Amino acid that can substitute for a portion of the vitamin deficient in this patient is which one of the following?
- Asparagine
- Methionine
- Proline
- Tryptophan
Correct

Incorrect

Explanation:

Tryptophan is an aromatic amino acid that contains an indole group. By a very complex series of minor enzymatic reactions, a small amount (-2%) of the tryptophan can be converted to quinolinate, which can then be used in place of niacin (nicotinic acid) in NAD (nicotinamide adenine dinucleotide) synthesis. Very high tryptophan levels can replace a portion of the dietary requirements for niacin. The nutritional disease pellagra (characterized by swollen tongue, dermatitis, neurologic dysfunction, and gastrointestinal dysfunction) usually occurs in the set-ting of combined tryptophan and niacin deficiency. Alanine, the amino acid with a methyl R group, is a substrate of the liver enzyme alanine amino transferase (ALT, formerly called SGPT). Asparagine is one of the sources of ammonia for the urea cycle. Methionine is a sulfur containing amino acid that is associated with associate with methyl group transfers. Proline is technically an imino acid, rather than an amino acid, with a ring structure. You should remember collagen has high proline concentration.
Question 31 of 36

31. Question
1 points
DNA studies of a 52 year old man with hepatitis showed that he was homozygous for the Z allele of alpha 1-antitrypsin, produced by a missense mutation that prevents the proper folding of the protein. Liver biopsy would most likely show accumulation of a proteinaceous substance in which subcellular site?
- Endoplasmic reticulum
- Extracellular matrix
- Golgi apparatus
- Inclusion bodies
Correct

Incorrect

Explanation:

The patient has liver disease secondary to homozygosity for the Z allele of alpha1-anti-trypsin. Alpha1-antitrypsin, more properly alpha1-antiproteinase, is synthesized and secreted into the blood by the liver and macrophages. It is the principle serine protease of the human plasma, and it inhibits trypsin, elastin, and other proteases. It exists in several isoforms. Proteins such as alpha1-antitrypsin that are normally secreted must fold properly in the endoplasmic reticulum in order to be transferred to the Golgi apparatus. Sporadic misfolded proteins will be escorted into the cytoplasm for degradation in proteasomes, but if the cell is accumulating large quantities, they accumulate in the endoplasmic reticulum. ZZ individuals produce large amounts of misfolded protein, which accumulates in the cisternae of the endoplasmic reticulum and causes hepatitis and cirrhosis. Extracellular matrix could not be a possibility because these misfolded proteins could not get into the Golgi apparatus, which is a necessary step on their way to being excreted. The misfolded proteins would be unable to proceed to the Golgi apparatus. “Inclusion bodies” is a nonspecific term describing aggregate material accumulating in cells. The lysosomal storage diseases result in inclusion bodies of material from endocytosis, phagocytosis, or autophagy that cannot be digested due to a lysosomal enzyme deficiency. Misfolded proteins would accumulate in the ER, not in lysosomes.
Question 32 of 36

32. Question
1 points
Nitric oxide is synthesized from
- Methionine
- Arginine
- Aspartic acid
- Nicotinamide
Correct

Incorrect

Explanation:

Arginine is the precursor for nitric oxide in humans.
Question 33 of 36

33. Question
1 points
Which one of the following is NOT high in cholesterol?
- Eggs
- Bacon
- Avocados
- Potatoes
Correct

Incorrect

Explanation:

Potatoes are not high in cholesterol, though frying them can increase their cholesterol content. The other foods are all high in cholesterol.

Question 34 of 36

34. Question

1 points

A person ingests ethylene glycol. The serum bicarbonate level is 16meq/L. The expected PCO2 in the blood is

20 mm Hg
24 mm Hg
28 mm Hg
32 mm Hg

Correct

Incorrect

Explanation:

Ethylene glycol causes a metabolic acidosis. By winter´s formula, in metabolic acidosis, PCO2 = 1.5(serum HCO3-) + 8 + 2 mm Hg. In this case, the expected PCO2 is 24 mm Hg. The other choices are mathematically incorrect.

Question 35 of 36

35. Question
1 points
Phenylketonuria belongs to which type of inborn error of metabolism?
- Lipid storage disease
- Disorder of lipoprotein metabolism
- Glycogen storage disease
- Disorder of amino leukodystrophy acid metabolism
Correct

Incorrect

Explanation:

Phenylketonuria is a disorder of amino acid metabolism in which there is a deficiency of phenylalanine hydroxylase.
Question 36 of 36

36. Question
1 points
Sanfilippo syndrome belongs to what type of inborn error of metabolism?
- Glycogen storage disease
- Disorder of amino leukodystrophy acid metabolism
- Disorder in purine and pyrimidine metabolism
- Mucopolysaccharidos dependency
Correct

Incorrect

Explanation:

Sanfilippo syndrome is a mucopolysaccharidosis in which there is abnormal accumulation of Heparan sulfate, a glycosaminoglycan.

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