Carbohydrate Metabolism Quiz (32 test)
1. Diarrhea from infection or malnutrition is the world’s most prevalent killer of A 2-month-old Caucasian girl develops chronic diarrhea and liver inflammation in early infancy when the mother begins using formula that includes corn syrup. Evaluation of the child demonstrates sensitivity to fructose in the diet. Which of the following glycosides contains fructose and therefore should be avoided when feeding or treating this infant?
2. Which of the following carbohydrates would be most abundant in the diet of strict vegetarians?
3. Alcohol abuse affects over 13% of adults in the United States, costing more health care dollars ($184 billion annually) than cancer ($107 billion) or obesity ($100 billion) in some studies. In 2001, 47% of those between ages 12 and 20 years reported drinking, 30% of these to binge drinking in the last month. Chronic alcoholics require more ethanol than do nondrinkers to become intoxicated because of a higher level of a specific enzyme. However, independent of specific enzyme levels, the availability of what other substance is rate-limiting in the clearance of ethanol?
4. In lung diseases such as emphysema or chronic bronchitis, there is chronic hypoxia that is particularly obvious in vascular tissues such as the lips or nail beds (cyanosis). Certain genetic diseases such as α1-antitrypsin deficiency (MIM*107400) predispose to emphysema, as do environmental exposures such as cigarette smoking or asbestos. Poorly perfused areas exposed to chronic hypoxia have decreased metabolic energy for tissue maintenance and repair. Which of the following is an important reason for this?
- Increased hexokinase activity owing to increased oxidative phosphorylation
- Increased ethanol formation from pyruvate on changing from anaerobic to aerobic metabolism
- Increased glucose utilization via the pentose phosphate pathway on changing from anaerobic to aerobic metabolism
- Decreased ATP generation and increased glucose utilization on changing from aerobic to anaerobic metabolism
- Decreased respiratory quotient on changing from carbohydrate to fat as the major metabolic fuel
5. An 18-year-old Korean college student attends a fraternity party and is embarrassed because he becomes flushed and sick to his stomach after his first drink of He learns that this reaction is due to genetic variation in some Asians and Native Americans that affects metabolism of a metabolite of alcohol. Which of the following is the variably degraded metabolite?
- Hydrogen peroxide
6. A 6-month-old Caucasian girl is hospitalized for evaluation of short stature, enlarged liver, and intermittent lethargy/irritability that, on a recent emergency room visit, was accompanied by low blood glucose (hypoglycemia). In the same ward is a 6-year-old African American boy who is being evaluated for severe muscle cramping that raised suspicions for sickle cell The family history is unremarkable for these children; each has a normal sibling and normal parents. Both children are given diagnoses of glycogen storage disease with the infant girl having type I (MIM*232200) affecting liver and the older boy type V (McArdle disease, MIM*232600) affecting mainly muscle. Which of the following conversions explains the difference in these presentations?
- Glycogen to lactate in liver
- Glycogen and lactate to glucose in liver
- Glycogen to glucose in muscle
- Glycogen to alanine in muscle
- Glycogen to glucose 6-phosphate in liver
7. A 3-day-old boy from an Iraqi refugee family exhibits severe tissue swelling (edema), rapid heart rate (tachycardia), enlargement of liver and spleen (hepatosplenomegaly), and jaundice of the eyes and skin. The couple had two prior female infants who are alive and well, and the wife relates that she lost a brother in infancy with severe hemolysis induced after a viral Blood tests show hemoglobin of 5 g/dL (normal neonate mean 18.5) with reticulocyte count of 15% (normal 1.8-4.6). Exchange transfusion is attempted but the child suffers cardiac arrest. Postmortem assay of red cell enzymes confirms the suspected diagnosis of glucose-6-phosphate dehydrogenase deficiency (MIM*305900), implying defective synthesis of which of the following compounds?
- Deoxyribose and NADP
- Glucose and lactate
- Lactose and NADPH
- Ribose and NADPH
- Sucrose and NAD
8. Which of the following best explains why fructose was formerly recommended for patients with diabetes mellitus?
- Fructose is a better substrate for hexokinase.
- Fructose stimulates residual insulin release.
- Fructose has a specific kinase in liver that allows bypass of phosphofructokinase.
- Fructose is phosphorylated and cleaved to triose phosphates, which cannot be used for gluconeogenesis.
- Hexokinase phosphorylates fructose in extrahepatic tissues, and its activity will not be affected by high glucose concentrations in diabetes.
9. A 2-month-old Caucasian girl is evaluated for hypoglycemia and lactic acidosis and noted to have an enlarged Biopsy reveals stored glycogen, and a glycogen storage disease is suspected. Assay of usual glycogen enzyme deficiencies in the liver specimen is normal, so the metabolic consultant recommends assay of rarer enzyme deficiencies that influence glycogen metabolism. These enzymes would most likely include which of the following?
- cAMP-dependent protein kinase
- Glucose-6-phosphate dehydrogenase
10. An 11-month-old infant with hypoglycemia and a palpable liver is evaluated for possible glycogen storage disease. The parents have immigrated from Russia, and report that the child’s older brother was diagnosed with a “debrancher” enzyme deficiency with similar glycogen This diagnosis would imply accumulation of glycogen with which type of glucose linkages?
- Linear α1 → 4 linkages with branching α1 → 6 linkages
- Linear α1 → 6 linkages with branching β1 → 4 linkages
- Linear β1 → 4 linkages only
- Linear β1 → 6 linkages only
- Branching β1 → 6 linkages only
11. A 7-year-old obese Hispanic girl presents with dehydration after 3 days of vomiting and Her parents mention that a sibling was diagnosed with a type of diabetes that spilled sugar into the urine but did not need treatment. Urine reagent strip test for reducing sugars is strongly positive. The physician obtains a blood glucose level that is normal and a urine glucose oxidase test on the urine is also negative for glucose. Further analysis of the urine reveals a small amount of fructose and a large amount of an unidentified pentose that is most likely which of the following?
12. A 2-week-old Caucasian boy returns to his pediatrician for evaluation of increased jaundice during his nursery stay and to follow up on a positive newborn screen for galactosemia (MIM*230400). Clinical assessment suggests the child’s jaundice has resolved and he has a good weight gain with no feeding The pediatrician obtains a repeat newborn screen, but recalls that certain carbohydrates can be recognized as reducing substances in urine by the Clinitest reaction that produces a green color. The urine reagent strip test is positive and physician suggests a switch to nonlactose formula until the nurse mentions that she spilled the urine and performed the test on a tabletop where sugar for coffee had been spilled. Among the following C6 isomers of glucose, which is a ketose and reducing substance?
13. Which of the following explains why individuals with hyperlipidemia and/or gout should minimize their intake of sucrose and high-fructose syrups?
- Fructose can bypass phosphofructokinase using a fructokinase in liver.
- Fructose can be phosphorylated by hexokinase in liver cells.
- Fructose is converted to UDP-fructose in liver.
- Fructose is ultimately converted to galactose in liver.
- Fructose can be phosphorylated by hexokinase in adipose cells.
14. A 14-year-old Caucasian adolescent with past history of drug/alcohol abuse is brought to the emergency room after she cannot be aroused for school; her parents think that a bottle of acetaminophen (Tylenol) in their medicine cabinet has fewer tablets than they The ER physician notes that cellulose is listed as the solid binder in the particular brand of acetaminophen. Since liver-protective N-acetylcysteamine therapy must be started within 16 hours of potential toxicity, the physician suggests that a rapid test for cellulose ingestion would be helpful in ascertaining if the child took the acetaminophen. Which of the following tests would be most informative regarding cellulose ingestion?
- Serum glucose to reflect intestinal digestion and absorption of cellulose
- Serum glucose after hydrolysis to break up cellulose β1 → 4 bonds
- Stool glucose after hydrolysis to break up cellulose β1 → 4 bonds
- Stool glucose to reflect intestinal digestion of ingested cellulose
- Stool glucose to reflect intestinal digestion of β1 → 4 bonds distal to β1 → 6 branching points in cellulose
15. A frequent presentation in the newborn period is transient hypoglycemia as the child adapts to separation from maternal glucose Blood glucose is generally maintained at concentrations of 4.5 to 5.5 mmol/L but may rise to 6.5 to 7.2 mmol/L after feeding or decrease to 3.3 to 3.9 mmol/L in the fasting state. Which of the following enzymes plays an important role in regulating blood glucose levels after feeding?
- Pyruvate kinase
- Glucose-6-phosphate dehydrogenase
16. A 5-year-old African American girl is brought to the emergency room with tonic-clonic seizures. Laboratory studies are drawn as anticonvulsants given do not completely stop the A blood glucose of 30 mg/dL (normal 60-100) is found, prompting administration of 25% dextrose intravenously and 1 mg of glucagon intramuscularly. Which of the following events will occur in response to glucagon?
- CO2 is consumed.
- Inorganic phosphate is consumed.
- Acetyl-CoA is utilized.
- ATP is generated.
- GTP is generated.
17. A 6-month-old Caucasian boy has exhibited somewhat slow growth but becomes very ill after contracting influenza from an older A plasma lactate level of 55 mg/dL is found that suggests underlying mitochondrial disease, and mitochondrial DNA studies confirm a large deletion that affects several oxidative- phosphorylation complexes. Exacerbation of routine illness by the child’s reduced energy reserves would most affect which of the following reactions of the citric acid cycle?
- Citrate → α-ketoglutarate
- α-Ketoglutarate → succinate
- Succinate → fumarate
- Fumarate → malate
- Malate → oxaloacetate
18. A 45-year-old African American female is found unconscious at her desk and rushed to the emergency room via She is a known diabetic, and an injectable insulin pen was found on her desk. Serum glucose was less than 20 g/dL as read by glucometer on the way to the hospital. Which of the following statements reflects the pathogenesis of her hypoglycemia?
- Her liver was suddenly permeable to glucose after added insulin.
- Her insulin increased glucose import into extrahepatic tissues using various glucose transporters.
- Her insulin stimulated liver glucokinase, which phosphorylates glucose only at low glucose concentrations.
- Her extrahepatic tissues became permeable to glucose through the opposing action of glucagon.
- Insulin stimulated glucose uptake into her liver even when the serum glucose became low.
19. Which of the following two compounds are the primary products of the pentose phosphate pathway?
- NAD+ and ribose
- NADH and ribose
- NADP+ and ribose
- NADPH and ribose
- NAD+ and glucose
- NADH and glucose
- NADP+ and glucose
- NADPH and glucose
20. Which of the following is an energy-requiring step of glycolysis?
- Lactate dehydrogenase
- Phosphoglycerate kinase
- Pyruvate kinase
- Phosphohexose isomerase
21. Which of the following are primary substrates for gluconeogenesis?
- Galactose and fructose
- Glycerol and alanine
- Acetyl-CoA and succinyl-CoA
- Sucrose and lactose
- GTP and biotin
22. A 3-month-old Caucasian girl presents with low blood glucose (hypoglycemia), enlarged liver (hepatomegaly), and excess fat deposition in the cheeks (cherubic facies). A liver biopsy reveals excess glycogen in Deficiency of which of the following enzymes best explains this phenotype?
23. An 18-year-old Hispanic female is evaluated for fainting spells that tend to occur when she has not eaten due to illness or work. Her body mass index [weight in kg/(height in m)2] is over 29 (<26 desirable) and the initial history makes anxiety or blood pressure changes Several random blood samples demonstrate lower glucose than normal and a glucose tolerance test is abnormal, showing a slow decrease in administered glucose that is suggestive of diabetes mellitus. Glucagon proves effective in helping her fainting spells, and a dietician places her on a moderate, low-carbohydrate diet, with monitoring of glucose by glucometer and use of glucagon when symptomatic. What is the role of glucagon in this situation?
- To stimulate the citric acid cycle when tissue resistance leads to excess insulin
- To stimulate gluconeogenesis when tissue resistance leads to excess insulin
- To stimulate glycolysis in the presence of decreased insulin secretion
- To stimulate the pentose phosphate pathway in the presence of decreased insulin secretion
- To stimulate glycogenolysis in the presence of decreased insulin secretion
24. A 2-year-old African American boy is evaluated for short stature (height below the 3rd percentile with weight and head circumference at the 20th percentile for age), irritability between meals accompanied by low glucose levels, enlarged liver, and easy bruisability. Liver biopsy reveals excess glycogen and deficiency of the α1→ 6 branching enzyme is documented for a diagnosis of type IV glycogen storage disease (MIM*232500). This disorder causes variable liver and neuromuscular symptoms but can be lethal due to progressive liver scarring (cirrhosis) because of the presence of abnormal glycogen. Conventional therapy with continuous glucose supply (eg, nocturnal cornstarch by tube) to minimize the need for glycogen breakdown is often not effective, and additional agents to minimize synthesis of abnormal glycogen have been considered. Inhibition of glycogen synthesis might target which of the following molecules?
- UDP-glucose 1-phosphate
- UDP-glucose 6-phosphate
- Glucose 6-phosphate
- Glucose 1-phosphate
25. Which of the following statements best describes the structure of glycogen?
- Glycogen is a copolymer of glucose and galactose.
- There are more branch residues than residues in straight chains.
- Branch points contain α1-4 glycosidic linkages.
- New glucose molecules are added to the C1 aldehyde group of chain termini, forming a hemiacetal.
- The monosaccharide residues alternate between D- and L-glucose.
26. A 25-year-old African American male notices increased fatigue and decreased performance when playing outfield for his office softball team. After a game in hot weather with many fielding chances, he has severe muscle pains and cramps that keep him awake and notices that his urine is dark that night. His physician suspects McArdle disease (type V glycogen storage disease—MIM*232600) and has him run on a treadmill breathing air with reduced oxygen. The man develops severe cramps after this ischemic exercise, further supporting the presumptive diagnosis. A diagnostic muscle biopsy is likely to show which of the following?
- Increased normal glycogen with deficient hexokinase
- Increased normal glycogen with deficient glycogen synthase
- Increased normal glycogen with deficient phosphorylase
- Decreased muscle glycogen with decreased glycogen synthase
- Decreased muscle glycogen with decreased debranching enzyme
27. The 10-year experience of a biochemical genetics laboratory includes five patients who had a positive urine reagent dipstick reaction for reducing sugars. Two of these were young females evaluated for vomiting and failure to thrive, while three were a boy and two girls, who were studied as part of a control population. Mass spectrometry profiles had shown a urine chemical with six carbons and a ketone group. Which of the following metabolites satisfy these chemical criteria and accumulate in specific inborn errors?
- Fructose, fructose 1-phosphate
- Galactose, galactose 1-phosphate
- Glucose, glucose 1-phosphate
- Ribulose, ribose 1-phosphate
- Xylulose, xylose 1-phosphate
28. A 17-year-old Caucasian adolescent is evaluated for fainting spells and found to have a glucose level of 54 mg/dL (normal 75-105) one hour after Her body mass index (BMI) is 17 (average 23-25), and physical examination reveals pallor, halitosis, and discolored teeth with multiple caries. An eating disorder is suspected, and she enlists in a research study that includes behavioral and dietary therapy along with metabolic studies. Administration of deuterium-labeled glucose shows initial rapid entry into liver and peripheral muscle followed by continued muscle but minimal liver intake. Which of the following accurately interprets these results?
- Abnormal liver uptake reflecting starvation
- Abnormal liver uptake reflecting latent diabetes mellitus
- Abnormal liver uptake reflecting prior glycogen depletion
- Normal liver uptake reflecting a lower Km for liver hexokinase
- Normal liver uptake reflecting a higher Km for liver glucokinase
29. The figure below depicts the initial steps of glycolysis with enzyme reactions A and E, and substrates B, C, and Which of the following options depicts the correct reaction sequence: 1—a reaction regulating glucose levels, 2—endergonic reaction(s), requiring ATP to ADP coupling, and 3—reaction(s), producing a substrate that will be reduced to produce NADH?
- 1-reaction A, 2-reactions A and B to C, 3-reactions C to D and E
- 1-reaction A, 2-reactions A and C to D, 3-reactions C to D and E
- 1-reaction A, 2-reaction B to C, 3-reactions B to C and E
- 1-reaction E, 2-reaction A, 3-reactions C to D and E
- 1-reaction E, 2-reaction E, 3-reactions C to D and E
30. A 14-year-old African American adolescent competes well in short distance events as she tries out for the track team but does poorly at longer Evaluation at a sports institute shows she has elevation of blood lactate after longer periods on a treadmill and suggests a defect in muscle energy metabolism. Although the girl’s parents decline further expensive evaluation, which of the following reactions of muscle metabolism would be least affected after she has run a long distance?
- Glucose 6-phosphate to fructose 6-phosphate
- Glucose to glucose 6-phosphate
- Fructose 6-phosphate to fructose 1,6-diphosphate
- Phosphoenolpyruvate to pyruvate
- Pyruvate to lactate
31. Which of the following enzymes catalyzes high-energy phosphorylation of substrates during glycolysis?
- Pyruvate kinase
- Phosphoglycerate kinase
- Triose phosphate isomerase
- Glyceraldehyde-3-phosphate dehydrogenase
32. Which reaction in the figure below occurs in both muscle and liver but has substantially different qualities in the two?
- Reaction A
- Reaction B
- Reaction C
- Reaction D
- Reaction E