[MCQs] Integrated Metabolism - Vitamins, Minerals, and Hormones - Part 1 (20 test)

Quizzes about Integrated Metabolism—Vitamins, Minerals, and Hormones - Part 1 (20 test)

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Question 1

A 48-year-old Caucasian male presents with congestive heart failure with elevated liver enzymes. His skin has a grayish pigmentation. The levels of liver enzymes are higher than those usually seen in congestive heart failure, suggesting an inflammatory process (hepatitis) with scarring (cirrhosis) of the liver. A liver biopsy discloses a marked increase in iron storage. In humans, molecular iron (Fe) is which of the following?

A	Stored primarily in the spleen
B	Stored in combination with ferritin
C	Excreted in the urine as Fe2+
D	Absorbed in the intestine by albumin
E	Absorbed in the ferric (Fe3+) form

Question 1 Explanation:

Ferrous iron (Fe2+) is the form absorbed in the intestine by ferritin, transported in plasma by transferrin, and stored in the liver in combination with ferritin or as hemosiderin (incorrect answers a, d, e). There is no known excretory pathway for iron, either in the ferric or ferrous form (incorrect answer c). For this reason, excessive iron uptake over a period of many years may cause hemochromatosis (MIM*235200), the likely diagnosis for this male. This is a condition of extensive hemosiderin deposition in the liver, myocardium, pancreas, and adrenals. The resulting symptoms include liver cirrhosis, congestive heart failure, diabetes mellitus, and changes in skin pigmentation.

Question 2

Intestinal bowel resections are necessary for autoimmune inflammatory diseases such as Crohn disease and for congenital anomalies such as malrotation or volvulus (twisted intestine with impaired blood supply). Once the absorptive intestinal mucosa falls below a certain length, oral or parenteral alimentation must be instituted to maintain nutrition. In such solutions, which of the following nutrients is most dispensable?

A	Protein
B	Iodine
C	Carbohydrates
D	Lipids
E	Calcium

Question 2 Explanation:

Certain amino acids and lipids are dietary necessities because humans cannot synthesize them. The energy usually obtained from carbohydrates can be obtained from lipids and the conversion of some amino acids to intermediates of the citric acid cycle (incorrect answers a, d). These alternative substrates can thus provide fuel for oxidation and energy plus reduce equivalents for biosynthesis. Iodine is important for thyroid hormone synthesis, whereas calcium is essential for muscle contraction and bone metabolism (incorrect answers b, e).

Question 3

A 40-year-old African American male is concerned about weight gain acquired during his stressful schedule as a small business executive. He embarks on a low- carbohydrate diet consisting of packaged or dried meats that are convenient for travel and office meals. Which of the following vitamins would most likely become deficient on this diet?

A	Thiamine
B	Niacin
C	Cobalamin
D	Pantothenic acid
E	Vitamin C

Question 3 Explanation:

Ascorbic acid (vitamin C) is found in fresh fruits (citrus, strawberries, and tomatoes) and vegetables (broccoli, potatoes, cabbage, and spinach). Pantothenic acid (vitamin B5) is found in most foods including meat and whole grains (incorrect answer d), as are niacin (vitamin B3—not strictly a vitamin since it can be synthesized—incorrect answer b), thiamine (vitamin B1—incorrect answer a), and cobalamin (vitamin B12— found in meat, milk, and eggs—incorrect answer c). Deficiency of ascorbic acid produces scurvy, the “sailor’s disease.” Ascorbic acid is necessary for the hydroxylation of proline to hydroxyproline in collagen, a process required in the formation and maintenance of connective tissue. The failure of mesenchymal cells to form collagen causes the skeletal, dental, and connective tissue deterioration seen in scurvy. Thiamine, niacin, cobalamin, and pantothenic acid can all be obtained from fish or meat products. The nomenclature of vitamins began by classifying fat-soluble vitamins as A (followed by subsequent letters of the alphabet such as D, E, and K) and water-soluble vitamins as B. Components of the B vitamin fraction were then given subscripts, eg, thiamine (B1), riboflavin (B2), niacin (nicotinic acid [B3]), pantothenic acid (B5), pyridoxine (B6), and cobalamin (B12). The water-soluble vitamins C, biotin, and folic acid do not follow the B nomenclature.

Question 4

Children with autism and other disorders with mental disability are often put on megavitamin supplements despite no scientific evidence of benefit. Although most vitamins are harmless in excess, merely being excreted in urine, vitamin A can be toxic. Which of the following accurately describes vitamin A?

A	It is not an essential vitamin.
B	It is related to tocopherol.
C	It is a component of rhodopsin.
D	It is derived from ethanol.
E	It is also known as opsin.

Question 4 Explanation:

The retinal pigment rhodopsin is composed of the 11-cis-retinal form of vitamin A coupled to opsin. Light isomerizes 11-cis-retinal to all-trans-retinal, which is hydrolyzed to free all-trans-retinal and opsin. In order for regeneration of rhodopsin to occur, 11-cisretinal must be regenerated. This dark reaction involves the isomerization of all-trans-retinal to 11-cis-retinal, which combines with opsin to reform rhodopsin. A deficiency of vitamin A, which is often derived from the β-carotene of plants, results in night blindness. Excess of vitamin A (hypervitaminosis A) can cause cerebral edema and other problems postnatally and severe birth defects when retinoids are taken prenatally (eg, women taking Accutane for acne).

Question 5

A 12-year-old Caucasian girl is hospitalized for evaluation of a possible seizure disorder because she has staring spells, lethargy, and irritability (not herself) once or twice per day. A 24-hour electroencephalogram shows diffuse epileptic foci that develop some 4 to 6 hours after feeding, and low serum glucose is noted during these periods. Which of the following dietary supplements might help this child?

A	Malate and niacin
B	Acetyl-CoA and biotin
C	Acetyl-CoA and thiamine pyrophosphate
D	Oxaloacetate and pyridoxine
E	Oxaloacetate and niacin

Question 5 Explanation:

Hypoglycemia during fasting suggests a disorder of gluconeogenesis, which involves the enzymes pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase to reverse key reaction steps in glycolysis. Pyruvate carboxylase catalyzes the conversion of pyruvate to oxaloacetate (incorrect answers d, e) and requires biotin with allosteric activation by acetyl-CoA. Biotin is a cofactor in several carboxylation reactions, while niacin is a source for NAD and NADH reactions (incorrect answers a, e) and pyridoxine for pyridoxal phosphate that is important in amino acid transferase reactions and steroid hormone action (incorrect answer d). Thiamine is important for pyruvate dehydrogenase, a first step in oxidative phosphorylation (incorrect answer c). High levels of acetyl-CoA indicate a fed state with oxidative breakdown of foods and high energy (ATP) levels. When ATP levels are high, oxaloacetate is consumed in gluconeogenesis, and when ATP levels are low, oxaloacetate enters the citric acid cycle. Gluconeogenesis only occurs in the liver and kidneys.

Question 6

A group of neurodegenerative diseases with onset ranging from neonates to adults have been found to involve deficiency of pantothenic acid kinase (eg, Hallervorden-Spatz disease, MIM*234200). The correlation between defective pantothenic acid activation and loss of myelin to cause neurodegenerative disease relates to its role in which of the following?

A	Decarboxylation reactions
B	Acetylation and acyl group metabolism
C	Dehydrogenation and redox reactions
D	Phosphorylation reactions
E	Methyl transfer reactions

Question 6 Explanation:

Pantothenic acid combines with the amino acid cysteine to become the pantetheine sulfhydryl component of coenzyme A (CoA) and acyl carrier protein (important for fatty acid synthesis). Acetyl-CoA is the activated form of acetate employed in acetylation reactions, including the citric acid cycle and lipid metabolism. Loss of myelin in Hallervorden-Spatz disease correlates with a role for activated pantothenic acid as a cofactor for fatty acid synthesis and as a carrier of acyl chains (which must be added to glycerol to form triacylglycerols), alkylacylglycerols (ether lipids), and (by acyl addition to sphingosine) cerebrosides, sphingomyelin, and gangliosides.

Question 7

Which of the following vitamins is the precursor of CoA?

A	Riboflavin
B	Pantothenate
C	Thiamine
D	Cobalamin
E	Pyridoxamine

Question 7 Explanation:

Pantothenate is the precursor of CoA, which participates in numerous reactions throughout the metabolic scheme. CoA is a central molecule of metabolism involved in acetylation reactions. Thus, a deficiency of pantothenic acid would have severe consequences. There is no documented deficiency state for pantothenate, however, because this vitamin is common in foodstuffs. Other choices are vitamins concerned with several metabolic pathways including electron transport (riboflavin, thiamine), organic acid conversion (cobalamin), and sulfhydryl group transfer (pyridoxamine).

Question 8

A 14-year-old Caucasian girl has been dieting to maximize her performance on the mile run with her track team. Although her lower weight initially improves her performance, she begins to fade in the last quartermile despite the exhortations of her trainer. She reports increasing muscle cramps and fatigue and undergoes stress testing that shows a progressive inefficiency of oxygen to energy conversion accompanied by increased blood lactate levels. Her sports medicine subspecialist attributes this to deficient fat stores and suggests a particular supplement. Which of the following would be most likely to benefit this patient?

A	Glycine and tyrosine
B	Thymidine
C	Pantothenic acid
D	Uridine
E	Folate

Question 8 Explanation:

Pantothenic acid (vitamin B5) is a component of coenzyme A (CoA) and acyl carrier protein (ACP). These proteins carry acyl groups with acetyl-CoA being important for fatty acid oxidation and many other metabolic reactions while ACP functions in fatty acid synthesis. Folic acid is made from glycine, serine, and choline, and is important for methyl (one carbon) reactions such as the conversion of deoxyuridine monophosphate to thymidine (incorrect answers a, b and d, e). Stable forms of folate (folinic acid, synthetic leucovorin) can be used as part of a supplement mixture (thiamine, riboflavin, coenzyme Q, and lipoic acid) for mitochondrial dysfunction. The reactive prosthetic group of both ACP and CoA is a phosphopantetheine sulfhydryl. In ACP, the phosphopantetheine group is attached to the 77-residue polypeptide chain via a serine hydroxyl. In CoA, the phosphopantetheine is linked to the 5′ phosphate of adenosine that is phosphorylated in its 3′ hydroxyl.

Question 9

Chronic alcoholics are at risk to develop lactic acidosis and neurologic symptoms, one example of which is the Wernicke-Korsakoff syndrome (MIM*277730). This complex of symptoms includes nerve problems such as nystagmus (oscillating eyes), ophthalmoplegia (deviated or weak eye), peripheral numbness/tingling, and cerebral problems such as confusion, delirium, coma, and memory loss in survivors. Explanation of why certain alcoholics get Wernicke-Korsakoff encephalopathy was suggested when altered transketolase (an important enzyme in the pentose phosphate pathway) was found in these individuals. Which of the following is most likely to be important in the development of lactic acidosis and/or Wernicke-Korsakoff susceptibility in alcoholics?

A	Thiamine pyrophosphate
B	Lipoamide
C	ATP
D	NADH
E	FADH

Question 9 Explanation:

Thiamine (vitamin B1) activated as its pyrophosphate is a cofactor for pyruvate dehydrogenase, α-ketoglutarate dehydrogenase of the citric acid cycle, branched chain ketoacid dehydrogenase that metabolizes leucine/isoleucine/valine, and transketolase of the pentose phosphate pathway. Deficiency of thiamine causes beriberi and exacerbates encephalopathy in alcoholics, having impact on the nervous system in both diseases. Since pyruvate dehydrogenase commits pyruvate from glycolysis to acetyl-CoA in the citric acid cycle, its impairment will increase lactate (lactic acidosis), deplete energy (by impacting the citric acid cycle and the first steps of oxidative phosphorylation), and impair glucose metabolism—all key to neural function. Impairment of transketolase and the pentose phosphate shunt would reduce NADPH production, key to glutathione maintenance and reduction of oxidants in brain. Certain mutations in transketolase may thus increase susceptibility to Wernicke-Korsakoff syndrome (MIM*277730), a nice example of a Mendelian enzyme alteration brought out by environment (alcohol dependency) to cause a multifactorial disease (encephalopathy). Lipoamide is also a cofactor in pyruvate dehydrogenase, transferring the acetyl group in pyruvate to coenzyme A. Lipoamide becomes acetyllipoamide and then dihydrolipoamide as it first accepts and then transfers an acyl group. This reaction and the regeneration of lipoamide are catalyzed by different parts of the dehydrogenase enzyme complex. ATP transfers phosphoryl groups, thiamine pyrophosphate transfers aldehyde groups, and NADH and FADH transfer protons. Mutations in the multipeptide pyruvate dehydrogenase complex occur in Leigh disease (MIM*256000), an end phenotype of many mutations that simulate the lactic acidosis and encephalopathy accompanying acute forms of thiamine deficiency (beriberi).

Question 10

Which of the following cofactors must be utilized during the conversion of acetyl-CoA to malonyl-CoA?

A	Thiamine pyrophosphate
B	Acyl carrier protein (ACP)
C	NAD1
D	Biotin
E	FAD

Question 10 Explanation:

The key enzymatic step of fatty acid synthesis is the carboxylation of acetyl-CoA to form malonyl-CoA; again there is the correlation of a carboxylation reaction and biotin (incorrect answers a-c, e). The carboxyl of biotin is covalently attached to an epsilon amino group of a lysine residue of acetyl-CoA carboxylase. The reaction occurs in two stages. In the first step, a carboxybiotin is formed: HCO3- + biotin-enzyme + ATP → CO2-biotin-enzyme + ADP + Pi In the second step, the CO2 is transferred to acetyl-CoA to produce malonyl-CoA: CO2-biotin-enzyme + acetyl-CoA → malonyl-CoA + biotin-enzyme None of the other cofactors listed are involved in this reaction.

Question 11

One of many roles for vitamins is their use as a reactive agent at the active sites of enzymes. Since these are catalytic reactions, the vitamin is not consumed in the reaction and is required in small amounts. Knowledge of this common mechanism should discourage use of megavitamin supplements that are promoted as cures for autism, cancer, and colds, but an unfortunate 30% of the American public admit to taking such supplements. Which of the following enzymes uses a vitamin-derived cofactor that is reoxidized by but different from NAD+?

A	Lactate dehydrogenase
B	Glutamate dehydrogenase
C	Pyruvate dehydrogenase
D	Malate dehydrogenase
E	Glyceraldehyde-3-phosphate dehydrogenase

Question 11 Explanation:

The vitamin riboflavin (vitamin B2) is a precursor of two cofactors involved in electron transport systems, riboflavin 5′-phosphate, also known as flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD). Strictly speaking, these compounds are not nucleotides, as they contain the sugar alcohol ribitol, not ribose. The cofactors are strongly bound to their apoenzymes and function as dehydrogenation catalysts. Pyruvate dehydrogenase is a multienzyme complex and contains the enzyme dihydrolipoyl dehydrogenase, which has, as its prosthetic group, two molecules of FAD per molecule of enzyme. In the overall reaction, the reduced FAD is reoxidized by NAD+. Mutations at several loci encoding the components of pyruvate dehydrogenase cause the clinical phenotype of Leigh syndrome (MIM*256000) with seizures, low muscle tone, neurodegeneration, and lactic acidosis. Succinate dehydrogenase also contains tightly bound FAD, one molecule per molecule of enzyme. Glutamate, lactate, malate, and glyceraldehyde-3-phosphate dehydrogenases all use nicotinamide dinucleotide cofactors and do not contain FAD as a prosthetic group.

Question 12

Which of the following foods should be emphasized for individuals with peripheral neuritis, insomnia, mouth and skin irritation, and diarrhea?

A	Human and cow (not goat) milk, uncooked fruits, and vegetables
B	Milk, eggs, meats, and fruits
C	Vegetables, cereals, and fruits
D	Liver, poultry, and eggs
E	Egg yolks, fish oils, and leafy vegetables

Question 12 Explanation:

Pyridoxine (vitamin B6) deficiency usually occurs concurrently with deficiency of other B vitamins or in association with drug therapy in individuals who are slow metabolizers for the antituberculosis drug isoniazid and others such as penicillamine or sulfa antibiotics (MIM*243400). Pyridoxine is present in many foods, particularly vegetables, cereals, and fruits. Niacin (precursor to nicotinamide adenine dinucleotide) is abundant in liver, poultry, and eggs; tetrahydrofolate in human and cow (not goat) milk, uncooked fruits, and vegetables; riboflavin (vitamin B2—precursor to flavin adenine mononucleotide) in milk, eggs, meats, and fruits; retinoic acid (vitamin A) in animal tissues such as egg yolks, fish oils with other carotenoids in leafy vegetables. The coenzyme pyridoxal phosphate is a versatile compound that aids in amino acid transaminations, deaminations, decarboxylations, and transulfurations. It is also important for operation of glycogen phosphorylase. A common feature of these reactions is formation of a Schiff-base intermediate with a specific lysine group at the active site of the appropriate enzymes

Question 13

Which of the following statements best describes vitamin A?

A	Vitamin A promotes maintenance of epithelial tissue.
B	Vitamin A is necessary for hearing but not for vision.
C	Vitamin A is synthesized in skin.
D	All vitamin A derivatives are safe to use during pregnancy.
E	Vitamin A is a form of calciferol.

Question 13 Explanation:

Vitamin A is essential for the normal differentiation of epithelial tissue as well as normal reproduction. Yellow and dark green vegetables as well as fruits are good sources of carotenes, which serve as precursors of vitamin A. However, egg yolk, butter, cream, and liver and kidneys are good sources of preformed vitamin A. Vitamin A is necessary for vision, not hearing. The visual pigment rhodopsin is formed from the protein opsin and 11-cis-retinal. During the photobleaching of rhodopsin, all-trans-retinal plus opsin is formed from dissociated rhodopsin, causing an impulse that is transmitted by the optic nerve to the brain. Isomerized from trans-retinal, 11-cis-retinal combines with opsin to reform rhodospin, making it ready for another photochemical cycle. All-trans-retinoic acid (tretinoin) has been found to be effective for topical treatment of psoriasis. Another form of vitamin A is 13-cis-retinoic acid (Accutane), which has been found to be effective in the treatment of severe cases of acne. Accutane causes birth defects of the face and brain if taken during the first trimester of pregnancy. Vitamin A is not synthesized in the skin. Vitamin D (derivatives of calciferol) can be synthesized in the skin under the influence of sunlight from 7-dehydrocholesterol, an intermediate in cholesterol synthesis.

Question 14

Which of the following conditions most rapidly produces a functional deficiency of vitamin K?

A	Coumadin therapy to prevent thrombosis in patients prone to clot formation
B	Broad-spectrum antibiotic therapy
C	Lack of red meat in the diet
D	Lack of citrus fruits in the diet
E	Premature birth

Question 14 Explanation:

Vitamin K is essential for the posttranscriptional modification of prothrombin by γ-carboxylation of glutamate residues. A functional deficiency exists in patients treated with analogs of vitamin K such as the Coumadin derivatives. The analogs act as anticoagulants by competing with vitamin K and preventing the production of functional prothrombin. By administration of vitamin K, hemorrhage can be prevented in such patients. Vitamin K is normally obtained from green, leafy vegetables in the diet (not from citrus fruits or red meat). Intestinal bacteria also synthesize the vitamin, but even broad-spectrum antibiotic therapy does not completely sterilize the intestine. A deficiency of vitamin K can cause hemorrhagic disease in newborn infants because their intestines do not have the bacteria that produce vitamin K and because vitamin K does not cross the placenta. The neonatal deficiency occurs in term or premature infants.

Question 15

A homeless 22-year-old Caucasian male is brought into the emergency room with psychotic imagery and alcohol on his breath. Which of the following compounds is most important to administer?

A	Glucose
B	Niacin
C	Nicotinic acid
D	Thiamine
E	Riboflavin

Question 15 Explanation:

Chronic alcoholics are at risk for thiamine deficiency, which is thought to play a role in the incoordination (ataxia) and psychosis that can become chronic (Wernicke-Korsakoff syndrome). The thiamine deficiency produces relative deficiency of the pyruvate dehydrogenase complex. The administration of glucose without checking glucose levels can therefore be dangerous, since excess glucose is converted to pyruvate by glycolysis. The low rate of pyruvate dehydrogenase conversion of pyruvate to coenzyme A (and entry into the citric acid cycle) causes pyruvate to be converted to lactate (through lactate dehydrogenase). Lactic acidosis can be fatal. Chronic alcoholics can be deficient in the other vitamins mentioned, but thiamine is most likely to help the neurologic symptoms.

Question 16

Which of the following vitamins becomes a major electron acceptor, aiding in the oxidation of numerous substrates?

A	Vitamin B6
B	Niacin
C	Riboflavin
D	Thiamine
E	Vitamin B1

Question 16 Explanation:

Nicotinamide adenine dinucleotide (NAD+) is the functional coenzyme derivative of niacin. It is the major electron acceptor in the oxidation of molecules, generating NADH, which is the major electron donor for reduction reactions. Thiamine (also known as vitamin B1) occurs functionally as thiamine pyrophosphate and is a coenzyme for enzymes such as pyruvate dehydrogenase. Riboflavin (vitamin B2) functions in the coenzyme forms of flavin mononucleotide (FMN) or flavin adenine dinucleotide (FAD). When concentrated, both have a yellow color due to the riboflavin they contain. Both function as prosthetic groups of oxidation-reduction enzymes or flavoproteins. Flavoproteins are active in selected oxidation reactions and in electron transport, but they do not have the ubiquitous role of NAD+

Question 17

Pantothenic acid is important for which of the following steps or pathways?

A	Pyruvate carboxylase
B	Fatty acid synthesis
C	Pyruvate carboxykinase
D	Gluconeogenesis
E	Glycolysis

Question 17 Explanation:

Pantothenic acid is phosphorylated and complexed with the amino acid cysteine to form 4- phosphopantetheine, the precursor for coenzyme A (CoA) and the acyl carrier protein (ACP) that participates in fatty acid synthesis. The thiol group of 4- phosphopantetheine is a carrier of acyl groups in CoA (A stands for acetylation or acetyl group) and ACP (fatty acyl groups). CoA is one of the major molecules in metabolism, carrying a pantetheine group bound to adenosine ribonucleotide-3′-phosphate via a 5′ diphosphate (pyrophosphate). Acetyl groups are linked to the reactive terminal sulfhydryl group to produce acetyl-CoA, which has a high acetyl transfer potential. CoA carries and transfers acetyl groups in much the same way as ATP transfers activated phosphoryl groups. CoA is involved in fatty acid synthesis, fatty acid β-oxidation, and the citric acid cycle; it is not involved in glycolysis or gluconeogenesis, where acetyl transfer does not occur. Gluconeogenesis generates glucose by converting pyruvate to oxaloacetate (via pyruvate carboxylase) to phosphoenopyruvate (via phosphoenopyruvate carboxykinase) to fructose 1,6-bisphosphate (through reversal of glycolytic enzymes) to fructose 6-phosphate (via fructose-1,6-bisphosphatase) to glucose 6- phosphate (through reversal of phosphohexose isomerase) to glucose (through glucose-6-phosphatase). Special enzymes are required at steps where reversal of glycolysis is not energetically feasible.

Question 18

Which of the following enzymes requires a vitamin that is rarely deficient except in those eating fad diets with excess raw egg white?

A	Pyruvate carboxylase
B	Pyruvate dehydrogenase
C	Phosphoenolpyruvate carboxykinase
D	Glucokinase
E	Fructokinase

Question 18 Explanation:

Biotin functions to transfer carbon dioxide to substrates, adding a carboxyl group. Pyruvate carboxylase and enzymes of the holocarboxylase complex that degrade organic acids (propionate, metabolites of leucine) require biotin to transfer an activated carbonyl group. Biotin may be depleted by a deficiency of the enzyme biotinidase (MIM*253260), rendering the mentioned carboxylases less active and producing accumulation of the mentioned organic acids with severe acidosis. Nutritional deficiency of biotin is virtually unknown, but can be induced with raw egg white, which contains avidin, a biotin-binding protein. Biotin deficiency causes skin rashes and hair loss, symptoms also seen in biotinidase enzyme deficiency. Thiamine is required for the reactions catalyzed by pyruvate dehydrogenase, transketolases, and α-ketoglutarate dehydrogenase. Kinases such as those in glycolysis require ATP as a cofactor.

Question 19

Neural tube defects such as anencephaly and spina bifida have higher frequencies in certain populations like those of Celtic origin and in certain regions such as South Texas. This suggestion of environmental cause produced research showing that deficiency of which of the following vitamins is associated with the occurrence of neural tube defects (anencephaly and spina bifida)?

A	Ascorbic acid (vitamin C)
B	Thiamine (vitamin B1)
C	Riboflavin (vitamin B2)
D	Niacin (vitamin B3)
E	Folic acid

Question 19 Explanation:

Spina bifida, or myelomeningocele, is a defect of the lower neural tube that produces an exposed spinal cord in the thoracic or sacral regions. Exposure of the spinal cord usually causes nerve damage and results in paralysis of the lower limbs and urinary bladder. Anencephaly is a defect of the anterior neural tube that results in lethal brain anomalies and skull defects. Folic acid is necessary for the development of the neural tube in the first few weeks of embryonic life, and the children of women with nutritional deficiencies have higher rates of neural tube defects. Because neural tube closure occurs at a time when many women are not aware that they are pregnant, it is essential that all women of childbearing age take a folic acid supplement of approximately 0.4 mg per day. Frank folic acid deficiency can also cause megaloblastic anemia because of a decreased synthesis of the purines and pyrimidines needed for cells to make DNA and divide. Deficiencies of thiamine in chronic alcoholics are related to Wernicke-Korsakoff syndrome, which is characterized by loss of memory, lackadaisical behavior, and a continuous rhythmic movement of the eyeballs. Thiamine dietary deficiency from excess of polished rice can cause beriberi. Niacin deficiency leads to pellagra, a disorder that produces skin rash (dermatitis), weight loss, and neurologic changes including depression and dementia. Riboflavin deficiency leads to mouth ulcers (stomatitis), cheilosis (dry, scaly lips), scaly skin (seborrhea), and photophobia. Because biotin is widely distributed in foods and is synthesized by intestinal bacteria, biotin deficiency is rare. However, the heat-labile molecule avidin, found in raw egg whites, binds biotin tightly and blocks its absorption, causing dermatitis, dehydration, and lethargy. Lactic acidosis results as a build-up of lactate due to the lack of functional pyruvate carboxylase when biotin is missing. Vitamin C deficiency leads to scurvy, which causes bleeding gums and bone disease. Vitamin B12 can be deficient due to a lack of intrinsic factor, which is a glycoprotein secreted by gastric parietal cells. A lack of intrinsic factor or a dietary deficiency of cobalamin can cause pernicious anemia and neuropsychiatric symptoms. The only known treatment for intrinsic factor deficiency (vitamin B12 deficiency) is intramuscular injection of cyanocobalamin throughout the patient’s life.

Question 20

After a meal and clearance of carbohydrates/chylomicrons from the bloodstream, blood glucose is initially maintained by liver glycogenolysis, then sustained by fat mobilization from adipose tissue. Children with glycogen storage disorders have immediate problems with glucose maintenance, while those with fatty acid oxidation disorders have later problems after glycogen is depleted. Which of the following mechanisms best explains the coordinate stimulation of glycogenolysis and lipolysis?

A	Cortisol, a glucocorticoid, alters transcription in liver and adipocytes.
B	Cortisol, a glucocorticoid, binds to liver and adipose plasma membrane receptors to increase cAMP.
C	Epinephrine diffuses into the cytosol of liver and adipose cells, activating phosphorylase kinase and triglyceride lipase by allosteric mechanisms.
D	Adenosine 3′,5′-cyclic monophosphate (cyclic AMP) is the second messenger in adipocytes, but not in the liver.
E	Epinephrine acts through the second messenger cAMP and protein kinases to stimulate glycogen phosphorylase and triglyceride lipase activities.

Question 20 Explanation:

Epinephrine (as well as glucagon) in liver stimulates adenylate cyclase and a kinase cascade ending with glycogen phosphorylase to initiate glycogenolysis. In adipose tissue, epinephrine more directly activates cyclic AMP, protein kinase, and triglyceride lipase to initiate lipolysis of stored triacylglycerides. Failure of glycogenolysis in glycogen storage diseases transmits a continuous signal of low glucose and enhanced fatty acid metabolism, causing high cholesterol and triglycerides. Normal glycogenolysis and failure of fat oxidation in fatty acid oxidation disorders causes hypoglycemia after glycogen is depleted, accompanied by deficient energy yield and carnitine depletion (from formation of abnormal acylcarnitines) that leads to lethal liver and heart failure. Some distinguish between type I hormones such as cortisol that diffuse into the cytosol and type II hormones such as epinephrine that interact with membrane receptors at the cell surface. The type I hormones form ligand-receptor complexes and mediate action in the cytosol or nucleus, while type II hormones often act through second messengers. Epinephrine and glucagon activate G protein complexes, changing cytosolic levels of adenosine 3′,5′-cyclic monophosphate (cyclic AMP) and modifying protein kinases. Cyclic AMP functions as a “second messenger” between the cell membrane and cytosolic or nuclear proteins.

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Part 1 (20 test) | Part 2 (18 test – end)

1. A 48-year-old Caucasian male presents with congestive heart failure with elevated liver His skin has a grayish pigmentation. The levels of liver enzymes are higher than those usually seen in congestive heart failure, suggesting an inflammatory process (hepatitis) with scarring (cirrhosis) of the liver. A liver biopsy discloses a marked increase in iron storage. In humans, molecular iron (Fe) is which of the following?

Stored primarily in the spleen
Stored in combination with ferritin
Excreted in the urine as Fe2+
Absorbed in the intestine by albumin
Absorbed in the ferric (Fe3+) form

2. Intestinal bowel resections are necessary for autoimmune inflammatory diseases such as Crohn disease and for congenital anomalies such as malrotation or volvulus (twisted intestine with impaired blood supply). Once the absorptive intestinal mucosa falls below a certain length, oral or parenteral alimentation must be instituted to maintain In such solutions, which of the following nutrients is most dispensable?

Protein
Iodine
Carbohydrates
Lipids
Calcium

3. A 40-year-old African American male is concerned about weight gain acquired during his stressful schedule as a small business He embarks on a low- carbohydrate diet consisting of packaged or dried meats that are convenient for travel and office meals. Which of the following vitamins would most likely become deficient on this diet?

Thiamine
Niacin
Cobalamin
Pantothenic acid
Vitamin C

4. Children with autism and other disorders with mental disability are often put on megavitamin supplements despite no scientific evidence of benefit. Although most vitamins are harmless in excess, merely being excreted in urine, vitamin A can be Which of the following accurately describes vitamin A?

It is not an essential vitamin.
It is related to tocopherol.
It is a component of rhodopsin.
It is derived from ethanol.
It is also known as opsin.

5. A 12-year-old Caucasian girl is hospitalized for evaluation of a possible seizure disorder because she has staring spells, lethargy, and irritability (not herself) once or twice per A 24-hour electroencephalogram shows diffuse epileptic foci that develop some 4 to 6 hours after feeding, and low serum glucose is noted during these periods. Which of the following dietary supplements might help this child?

Malate and niacin
Acetyl-CoA and biotin
Acetyl-CoA and thiamine pyrophosphate
Oxaloacetate and pyridoxine
Oxaloacetate and niacin

6. A group of neurodegenerative diseases with onset ranging from neonates to adults have been found to involve deficiency of pantothenic acid kinase (eg, Hallervorden-Spatz disease, MIM*234200). The correlation between defective pantothenic acid activation and loss of myelin to cause neurodegenerative disease relates to its role in which of the following?

Decarboxylation reactions
Acetylation and acyl group metabolism
Dehydrogenation and redox reactions
Phosphorylation reactions
Methyl transfer reactions

7. Which of the following vitamins is the precursor of CoA?

Riboflavin
Pantothenate
Thiamine
Cobalamin
Pyridoxamine

8. A 14-year-old Caucasian girl has been dieting to maximize her performance on the mile run with her track team. Although her lower weight initially improves her performance, she begins to fade in the last quartermile despite the exhortations of her trainer. She reports increasing muscle cramps and fatigue and undergoes stress testing that shows a progressive inefficiency of oxygen to energy conversion accompanied by increased blood lactate Her sports medicine subspecialist attributes this to deficient fat stores and suggests a particular supplement. Which of the following would be most likely to benefit this patient?

Glycine and tyrosine
Thymidine
Pantothenic acid
Uridine
Folate

9. Chronic alcoholics are at risk to develop lactic acidosis and neurologic symptoms, one example of which is the Wernicke-Korsakoff syndrome (MIM*277730). This complex of symptoms includes nerve problems such as nystagmus (oscillating eyes), ophthalmoplegia (deviated or weak eye), peripheral numbness/tingling, and cerebral problems such as confusion, delirium, coma, and memory loss in Explanation of why certain alcoholics get Wernicke-Korsakoff encephalopathy was suggested when altered transketolase (an important enzyme in the pentose phosphate pathway) was found in these individuals. Which of the following is most likely to be important in the development of lactic acidosis and/or Wernicke-Korsakoff susceptibility in alcoholics?

Thiamine pyrophosphate
Lipoamide
ATP
NADH
FADH

10. Which of the following cofactors must be utilized during the conversion of acetyl-CoA to malonyl-CoA?

Thiamine pyrophosphate
Acyl carrier protein (ACP)
NAD1
Biotin
FAD

11. One of many roles for vitamins is their use as a reactive agent at the active sites of enzymes. Since these are catalytic reactions, the vitamin is not consumed in the reaction and is required in small Knowledge of this common mechanism should discourage use of megavitamin supplements that are promoted as cures for autism, cancer, and colds, but an unfortunate 30% of the American public admit to taking such supplements. Which of the following enzymes uses a vitamin-derived cofactor that is reoxidized by but different from NAD+?

Lactate dehydrogenase
Glutamate dehydrogenase
Pyruvate dehydrogenase
Malate dehydrogenase
Glyceraldehyde-3-phosphate dehydrogenase

12. Which of the following foods should be emphasized for individuals with peripheral neuritis, insomnia, mouth and skin irritation, and diarrhea?

Human and cow (not goat) milk, uncooked fruits, and vegetables
Milk, eggs, meats, and fruits
Vegetables, cereals, and fruits
Liver, poultry, and eggs
Egg yolks, fish oils, and leafy vegetables

13. Which of the following statements best describes vitamin A?

Vitamin A promotes maintenance of epithelial tissue.
Vitamin A is necessary for hearing but not for vision.
Vitamin A is synthesized in skin.
All vitamin A derivatives are safe to use during pregnancy.
Vitamin A is a form of calciferol.

14. Which of the following conditions most rapidly produces a functional deficiency of vitamin K?

Coumadin therapy to prevent thrombosis in patients prone to clot formation
Broad-spectrum antibiotic therapy
Lack of red meat in the diet
Lack of citrus fruits in the diet
Premature birth

15. A homeless 22-year-old Caucasian male is brought into the emergency room with psychotic imagery and alcohol on his breath. Which of the following compounds is most important to administer?

Glucose
Niacin
Nicotinic acid
Thiamine
Riboflavin

16. Which of the following vitamins becomes a major electron acceptor, aiding in the oxidation of numerous substrates?

Vitamin B6
Niacin
Riboflavin
Thiamine
Vitamin B1

17. Pantothenic acid is important for which of the following steps or pathways?

Pyruvate carboxylase
Fatty acid synthesis
Pyruvate carboxykinase
Gluconeogenesis
Glycolysis

18. Which of the following enzymes requires a vitamin that is rarely deficient except in those eating fad diets with excess raw egg white?

Pyruvate carboxylase
Pyruvate dehydrogenase
Phosphoenolpyruvate carboxykinase
Glucokinase
Fructokinase

19. Neural tube defects such as anencephaly and spina bifida have higher frequencies in certain populations like those of Celtic origin and in certain regions such as South This suggestion of environmental cause produced research showing that deficiency of which of the following vitamins is associated with the occurrence of neural tube defects (anencephaly and spina bifida)?

Ascorbic acid (vitamin C)
Thiamine (vitamin B1)
Riboflavin (vitamin B2)
Niacin (vitamin B3)
Folic acid

20. After a meal and clearance of carbohydrates/chylomicrons from the bloodstream, blood glucose is initially maintained by liver glycogenolysis, then sustained by fat mobilization from adipose tissue. Children with glycogen storage disorders have immediate problems with glucose maintenance, while those with fatty acid oxidation disorders have later problems after glycogen is Which of the following mechanisms best explains the coordinate stimulation of glycogenolysis and lipolysis?

Cortisol, a glucocorticoid, alters transcription in liver and adipocytes.
Cortisol, a glucocorticoid, binds to liver and adipose plasma membrane receptors to increase cAMP.
Epinephrine diffuses into the cytosol of liver and adipose cells, activating phosphorylase kinase and triglyceride lipase by allosteric mechanisms.
Adenosine 3′,5′-cyclic monophosphate (cyclic AMP) is the second messenger in adipocytes, but not in the liver.
Epinephrine acts through the second messenger cAMP and protein kinases to stimulate glycogen phosphorylase and triglyceride lipase activities.

Integrated Metabolism

[MCQs] Integrated Metabolism – Vitamins, Minerals, and Hormones – Part 1 (20 test)

Quizzes about Integrated Metabolism—Vitamins, Minerals, and Hormones - Part 1 (20 test)

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[MCQs] Lipid, Amino Acid, Nucleotide, and Nitrogen Metabolism Quiz – Part 2 (18 test – end)

[MCQs] Integrated Metabolism—Vitamins, Minerals, and Hormones – Part 2 (18 test – end)

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