Question 1

A 10-year-old boy has suffered from slowly progressing ataxia (poor motor coordination)  since the age of 5.A blood test shows abnormal elevations of alanine and lactic acid levels after an oral glucose load.Partial deficiency of which of the following enzymes or transporters is the most likely cause of the boy's condition?

Accepted Answer

A)  Carnitine-palmitoyl transferase 1.
B)  Glucose transporter 4.
C)  Pyruvate dehydrogenase.
D)  Aldolase B.
E)  Glyceraldehyde-3-phosphate dehydrogenase.F) C) and D)
G) A) and B) C

Question 2

A 3-month-old infant is found to have fasting hypoglycemia.In order to test for possible enzyme deficiencies, you conduct a liver biopsy and test for several metabolic enzymes.Fasting hypoglycemia can be caused by deficiencies of all the following enzymes except:

Accepted Answer

A)  Glucose-6-phosphatase.
B)  Glucose-6-phosphate dehydrogenase.
C)  Glycogen phosphorylase.
D)  Phosphorylase kinase.
E)  Fructose-1,6-bisphosphatase.F) A) and D)
G) None of the above

Question 3

Which liver enzyme is activated by insulin to stimulate glycogen deposition by glycogen synthase?

Accepted Answer

A)  Phosphofructokinase-2.
B)  Protein phosphatase-1.
C)  Protein kinase A.
D)  Protein kinase C.
E)  Calmodulin-dependent protein kinase.F) A) and C)
G) C) and E) B

Question 4

A 30-year-old man of Italian ancestry is treated with high doses of a combination antibiotic for his chronic sinusitis.After 1 week of drug treatment, a dark brown discoloration of the urine is noted, and the hematocrit is found to be 32%.Haptoglobin is virtually undetectable.What is a likely mechanism for the patient's drug-induced anemia?

Accepted Answer

A)  Galactose metabolism is inhibited.
B)  There is not enough ribose to support DNA replication.
C)  Red blood cells produce too much apo-hemoglobin.
D)  Glutathione reduction by the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH)  is impaired.
E)  The reduced form of nicotinamide adenine dinucleotide (NADH)  oxidase overproduces oxygen radicals.F) B) and D)
G) A) and E)

Question 5

The activation of glucagon receptors turns the liver into a net producer of glucose.Glucagon stimulates a signal transduction pathway in liver involving:

Accepted Answer

A)  SMAD protein phosphorylation.
B)  Protein kinase A activation.
C)  Calcium pumping into the endoplasmic reticulum.
D)  Receptor tyrosine protein kinase activation.
E)  Activation of G protein guanosine triphosphatase (GTPase)  activity.F) None of the above
G) C) and D)

Question 6

A 25-year-old man is found in a semicomatose state and is taken to the emergency room by friends, who say that the man has not eaten for the past 5 days.Which of the following substances is this patient's primary source of glucose?

Accepted Answer

A)  Amino acids from liver proteins.
B)  Amino acids from muscle proteins.
C)  Liver glycogen.
D)  Muscle glycogen.
E)  Fatty acids from adipose tissue.F) A) and D)
G) B) and C)

Question 7

Glucokinase is used by liver and pancreatic b cells to adjust glucose metabolism to changing levels of blood glucose.This is possible because there is an important difference between glucokinase and the other isoforms of hexokinase:

Accepted Answer

A)  Glucokinase uses ATP as a substrate, but hexokinase does not.
B)  Glucokinase has a higher Km value for glucose than does hexokinase.
C)  Glucokinase has a maximal reaction rate (Vmax)  that changes with the blood glucose concentration.
D)  Glucokinase uses both glucose and fructose as substrates, whereas the other forms of hexokinase can use only glucose.
E)  Glucokinase is located on the cell surface, whereas the other forms of hexokinase are cytoplasmic.F) B) and E)
G) C) and E)

Question 8

Fructose-2,6-bisphosphate is an allosteric inhibitor of which enzyme of carbohydrate metabolism?

Accepted Answer

A)  Glucose-6-phosphate dehydrogenase.
B)  Phosphofructokinase-1.
C)  Aldolase B.
D)  Glycogen phosphorylase.
E)  Fructose-1,6-bisphosphatase.F) B) and C)
G) A) and E)

Question 9

As shown in Figure 22.4, a patient has low blood glucose levels (dashed line)  after a 24-hour fast.Normal values are indicated by the solid line.  A partial deficiency of which of the following enzymes could possibly be a cause of the fasting hypoglycemia?

Accepted Answer

A)  Pyruvate dehydrogenase.
B)  Glucokinase.
C)  Phosphofructokinase-1.
D)  Aldolase A.
E)  Pyruvate kinase.F) None of the above
G) A) and E) D

Exam 22: Carbohydrate Metabolism

Correct Answer
verified
C

A 3-month-old infant is found to have fasting hypoglycemia.In order to test for possible enzyme deficiencies, you conduct a liver biopsy and test for several metabolic enzymes.Fasting hypoglycemia can be caused by deficiencies of all the following enzymes except:

Correct Answer
verified

Which liver enzyme is activated by insulin to stimulate glycogen deposition by glycogen synthase?

Correct Answer
verified
B

Correct Answer
verified

The activation of glucagon receptors turns the liver into a net producer of glucose.Glucagon stimulates a signal transduction pathway in liver involving:

Correct Answer
verified

A 25-year-old man is found in a semicomatose state and is taken to the emergency room by friends, who say that the man has not eaten for the past 5 days.Which of the following substances is this patient's primary source of glucose?

Correct Answer
verified

Glucokinase is used by liver and pancreatic b cells to adjust glucose metabolism to changing levels of blood glucose.This is possible because there is an important difference between glucokinase and the other isoforms of hexokinase:

Correct Answer
verified

Fructose-2,6-bisphosphate is an allosteric inhibitor of which enzyme of carbohydrate metabolism?

Correct Answer
verified

As shown in Figure 22.4, a patient has low blood glucose levels (dashed line) after a 24-hour fast.Normal values are indicated by the solid line. A partial deficiency of which of the following enzymes could possibly be a cause of the fasting hypoglycemia?

Correct Answer
verified
D

Exam 22: Carbohydrate Metabolism

Correct AnswerverifiedC

A 3-month-old infant is found to have fasting hypoglycemia.In order to test for possible enzyme deficiencies, you conduct a liver biopsy and test for several metabolic enzymes.Fasting hypoglycemia can be caused by deficiencies of all the following enzymes except:

Correct AnswerverifiedShow Answer

Which liver enzyme is activated by insulin to stimulate glycogen deposition by glycogen synthase?

Correct AnswerverifiedB

Correct AnswerverifiedShow Answer

The activation of glucagon receptors turns the liver into a net producer of glucose.Glucagon stimulates a signal transduction pathway in liver involving:

Correct AnswerverifiedShow Answer

A 25-year-old man is found in a semicomatose state and is taken to the emergency room by friends, who say that the man has not eaten for the past 5 days.Which of the following substances is this patient's primary source of glucose?

Correct AnswerverifiedShow Answer

Glucokinase is used by liver and pancreatic b cells to adjust glucose metabolism to changing levels of blood glucose.This is possible because there is an important difference between glucokinase and the other isoforms of hexokinase:

Correct AnswerverifiedShow Answer

Fructose-2,6-bisphosphate is an allosteric inhibitor of which enzyme of carbohydrate metabolism?

Correct AnswerverifiedShow Answer

As shown in Figure 22.4, a patient has low blood glucose levels (dashed line) after a 24-hour fast.Normal values are indicated by the solid line. A partial deficiency of which of the following enzymes could possibly be a cause of the fasting hypoglycemia?

Correct AnswerverifiedD

Correct Answer
verified
C

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B

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Correct Answer
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Correct Answer
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Correct Answer
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Correct Answer
verified
D