LE 4.3 (2025) from LE 3

Question 1

8. Which serves as substrates for UDP-glucose synthesis?
   A. UTP & glucose-1-PO4
   B. GTP & fructose 1-6bisPO4
   C. UTP & glucose-6-PO4
   D. ATP & fructose 2-6bisPO4

Answer 1

A. UTP & glucose-1-PO4

A. Uridine diphosphate glucose synthesis
α-D-Glucose attached to uridine diphosphate (UDP) is the source of all the glucosyl residues that are added to the growing glycogen molecule. UDP-glucose (Fig. 11.4) is synthesized from GLUCOSE 1-PHOSPHATE AND UTP by UDP–glucose pyrophosphorylase (Fig. 11.5). Pyrophosphate (PPi), the second product of the reaction, is hydrolyzed to two inorganic phosphates (Pi) by pyrophosphatase. The hydrolysis is exergonic, which ensures that the UDP–glucose pyrophosphorylase reaction proceeds in the direction of UDP-glucose production. (Note: Glucose 1-phosphate is generated from glucose 6-phosphate by
phosphoglucomutase. Glucose 1,6-bisphosphate is an obligatory intermediate in this reversible reaction [Fig. 11.6].)
(Lippincott Illustrated Reviews 8th Edition, p. 272)

Question 2

9. Which enzyme synthesizes UDP-glucose?
   A. phosphoglucomutase
   B. glycogen synthase
   C. nucleoside diphosphokinase
   D. UDP-Glucose-pyrophosphorylase

Answer 2

D. UDP-Glucose-pyrophosphorylase

A. Uridine diphosphate glucose synthesis
α-D-Glucose attached to uridine diphosphate (UDP) is the source of all the glucosyl residues that are added to the growing glycogen molecule. UDP-glucose (Fig. 11.4) is synthesized from glucose 1-phosphate and UTP by ““UDP-glucose-phosphorylase”” (Fig. 11.5). Pyrophosphate (PPi), the second product of the reaction, is hydrolyzed to two inorganic phosphates (Pi) by pyrophosphatase. The hydrolysis is exergonic, which ensures that the UDP–glucose pyrophosphorylase reaction proceeds in the direction of UDP-glucose production. (Note: Glucose 1-phosphate is generated from glucose 6-phosphate by
phosphoglucomutase. Glucose 1,6-bisphosphate is an obligatory intermediate in this reversible reaction [Fig. 11.6].)
(Lippincott Illustrated Reviews 8th Edition, p. 272)

Question 3

22. Which enzyme, when insulin to glucagon ratio is high, is activated?
    A. protein phosphatase
    B. phosphorylase
    C. phosphorylase kinase
    D. protein phosphatase inhibitor

Answer 3

A. protein phosphatase

V. GLYCOGENESIS AND GLYCOGENOLYSIS REGULATION
A. Covalent activation of glycogenolysis
5. Phosphorylated state maintenance: The phosphate groups added to phosphorylase kinase and phosphorylase in response to cAMP are maintained because the enzyme that hydrolytically removes the phosphate, protein phosphatase-1 (PP1), is inactivated by inhibitor proteins that are also phosphorylated and activated in response to cAMP (see Fig. 11.9). Because insulin also activates the phosphodiesterase that degrades
cAMP, it opposes the effects of glucagon and epinephrine.

Question 4

23. Which glycogen storage disease involves a deficiency of a unique enzyme of gluconeogenesis?
    A. Pompe’s
    B. von Gierke’s
    C. Anderson’s
    D. Her’s

Answer 4

B. von Gierke’s

Gluconeogenesis : Enzymes that by-pass irreversible steps
Pyruvate carboxylase

Phosphoenolpyruvate carboxykinase

Fructose-1,6-phosphatase

Glucose-6-phosphatase (Type Ia: von Gierke’s)

Question 5

24. Which glycogen storage disease is caused by a deficiency of an important enzyme of glycolysis:
    A. Pompe’s
    B. von Gierke’s
    C. Tarui’s
    D. Her’s

Answer 5

C. Tarui’s

Glycolysis (Irreversible Steps) : Enzymes
Hexokinase/Glucokinase

Phosphofructokinase (Rate-limiting step) : Type VII : Tauri’s

Pyruvate Kinase

Question 6

25. Which glycogen storage disease is caused by a deficiency of muscle phosphorylase?
    A. Her’s
    B. McArdle’s
    C. Cori’s
    D. Fanconi

Answer 6

B. McArdle’s

Question 7

26. The products of the Pentose Phosphate Pathway are:
    A. 2 NADPH, 1 carbon dioxide, 2 Ribose
    B. 2 NADPH, 1 carbon dioxide, Ribose
    C. 2 NADPH, 2 carbon dioxide, Ribose
    D. 1 NADPH, 2 carbon dioxide, 2 Ribose

Answer 7

B. 2 NADPH, 1 carbon dioxide, Ribose

Question 8

27. Biosynthesis of Fatty Acids occur in the:
    A. Mammary Glands
    B. Ovaries
    C. Adrenals
    D. Liver

Answer 8

D. Liver

Question 9

28. Uses of NADPH include:
    A. Degradation of Nitric Oxide
    B. Oxidation of Hydrogen Peroxide
    C. Phagocytosis of Red Blood Cells
    D. Reductive Biosynthesis

Answer 9

D. Reductive biosynthesis

Question 10

29. A breast fed infant began to vomit frequently and lose weight. Several days later she developed jaundice, hepatomegaly and bilateral cataract. What is the possible cause for these symptoms.
    A. G6PD Deficiency
    B. Galactosemia
    C. Von Gierke’s Syndrome
    D. Hereditary Fructose Intolerance

Answer 10

B. Galactosemia

Question 11

30.The Uronic Acid Pathway:

A. Catalyzes conversion of glucose to glucuronic, pentoses, sialic acid.
B. Energy producing reaction
C. Occurs in the cytosol
D. Alternative pathway for the oxidation of glucose

Answer 11

D. Alternative pathway for the oxidation of glucose

Question 12

31.The rate limiting step in glycolysis is catalyzed by this enzyme and is bypassed in the metabolism of fructose
A. Phosphofructokinase I
B. Glucose-6-Phosphate
C. Glucose-1-Phosphate
D. Glucokinase

Answer 12

A. Phosphofructokinase

Glycolysis (Irreversible Steps) : Enzymes
Hexokinase/Glucokinase

Phosphofructokinase (Rate-limiting step) : Type VII : Tauri’s

Pyruvate Kinase

Question 13

32.Hexokinase has a low affinity for:
A. Fructose-6-Phosphate
B. Fructose-1-Phosphate
C. Fructose
D. Sucrose

Answer 13

C. Fructose

Question 14

33. Fructose-1 Phosphate reaction to Glyceraldehyde is catalyzed by:
    A. Aldolase A
    B. Aldolase B
    C. Aldolase C
    D. All of the above

Answer 14

B. Aldolase B

Question 15

34. Hereditary Fructose Intolerance is caused by a deficiency
    in this enzyme:
    A. Aldolase A
    B. Aldolase B
    C. Aldolase C
    D. All of the above

Answer 15

B. Aldolase B

Question 16

35. Classic Galactosemia is caused by this enzyme deficiency:
    A. GALT
    B. Galactokinase
    C. Galactomutase
    D. Phosphogalactogen

Answer 16

A. GALT

Question 17

36. Fructose -6-Phosphate can be produced from:
    A. Mannose-6-Phospate
    B. Sedoheptulase-6-Phosphate
    C.Xylulose-7-Phosphate
    D. All of the Above

Answer 17

A. Mannose-6-Phosphate

Question 18

37. Familial fructokinase deficiency causes no symptoms because:
    A. Hexokinase can phosphorylate fructose
    B. Liver aldolase can metabolize it
    C. Excess fructose is excreted through feces
    D. Excess fructose is converted to glucose

Answer 18

A. hexokinase can phosphorylate fructose

Question 19

38. A medical student developed hemolytic anemia after taking
    the oxidizing malarial drug primaquine. This severe reaction is most likely due to:
    A. Glucose-6-phosphate dehydrogenase deficiency
    B. Scurvy
    C. Diabetes
    D. Glycogen phosphorylase activity

Answer 19

A. Glucose-6-phosphate dehydrogenase deficiency

Question 20

39. G6PD is most severe in RBC’s because:
    A.The Pentose Phosphate Pathway is the sole source of NADPH in RBC’s
    B. RBC’s have nucleus and can produce ribulose-5-phosphate
    C. More NADPH is needed in RBC’s to reduce glutathione
    D. Glucose-6-Phosphate is consumed in RBC’s

Answer 20

A. The Pentose Phosphate Pathway is the sole source of NADPH in RBC’s

Question 21

40. True about G6PD:
    A. characterized by hemolytic anemia
    B. does not affect life expectancy
    C. Common in Middle America, Europe, and Africa
    D. symptomatic

Answer 21

A. Characterized by hemolytic anemia

Question 22

41. Substances that may make people with G6PD symptomatic:
    A. Fava beans
    B. Anti Tuberculosis drugs
    C. Anti-Inflammatories
    D. All of the above

Answer 22

A. Fava beans

Question 23

42. True of Fructose metabolism:
    A. sucrose yields 2 fructose and 1 glucose
    B. insulin dependent
    C. bypasses phosphofructokinase-1
    D. all of the above

Answer 23

C. bypasses phosphofructokinase-1

Question 24

43. Ribulose 5 Phosphate is an important product of Pentose Phosphate Pathway because:
    A. it is a substrate for fatty acid synthesis
    B. It is a substrate for steroid synthesis
    C. It is a substrate for nucleotide synthesis
    D. all of the above

Answer 24

D. All of the above

Question 25

44.Coenzyme responsible for the dehydrogenation of Glucose 6 Phosphate: A. NADP+ B. NADPH C. NADP+ and NADPH D. NAD

Answer 25

A. NADP+

Question 26

45.True of the Pentose Phosphate Pathway A. Occurs in the cytoplasm B. Has three irreversible reactions C. Produces ATP D. Produces Ribose

Answer 26

D. Produces ribose

Question 27

46.Major storage form of energy in the body. A. Glycogen B. Glucose C. Cellulose D. Starch

Answer 27

A. Glycogen

Question 28

48.The only tissue with glycerol kinase to phosphorylate glycerol. A. Brain B. Liver C. Pancreas D. Small intestines

Answer 28

B. Liver

Question 29

49.This sugar derivative is vital in the synthesis of collagen. A. Glucuronic acid B. Hyaluronic acid C. Ascorbic acid D. Sorbitol

Answer 29

C. Ascorbic acid Vitamin C (ascorbic acid) functions as a coenzyme in the hydroxylation of proline and lysine in the synthesis of collagen, a fibrous protein of the extracellular matrix. (Lippincott Illustrated Reviews 8th Edition, p. 1526)

Question 30

52.A 10 yrs old female was brought to the emergency room secondary to alterations in behaviour. On lab exam ,ketones are found in her urine. Which of the following is the most likely source of ketones? A. glycogenolysis B. glycolysis C. gluconeogenesis D. fatty acid breakdown

Answer 30

D. fatty acid breakdown Primary source (ATP) : Glucose Secondary source (ATP) : Ketone Bodies (Low BG, Fasting State) Metabolic Products: Glycogenolysis · Glycogen → Glucose Glycolysis · Glucose → 2 Pyruvate Gluconeogenesis · Non-carbohydrate (OAA, Lactic acid, Glycerol) → Glucose Fatty acid breakdown (β-oxidation) · Fatty Acid → Acetyl-CoA o Ketogenesis : Acetyl – CoA → Ketone Bodies

Question 31

53.Aldose reductase is an enzyme abundant in the following tissues except: A. liver B. nerve tissue C. seminal vesicles D. muscles

Answer 31

D. muscles Synthesis of sorbitol: Aldose reductase reduces glucose, producing sorbitol This enzyme is found in many tissues, including the lens, retina, Schwann cells of peripheral nerves, liver, kidney, placenta, red blood cells, and in cells of the ovaries and seminal vesicles. (P139 – Lippincott)

Question 32

56.Glucose is maintained in the blood as the sole energy source for the ______ in the non-starving state and as an available energy source for all other tissues A. liver B. brain C. lungs D. kidneys

Answer 32

B. brain A constant source of blood glucose is an absolute requirement for human life. Glucose is the greatly preferred energy source for the brain, and the required energy source for cells with few or no mitochondria, such as mature erythrocytes. Glucose is also essential as an energy source for exercising muscle, where it is the substrate for anaerobic glycolysis. (P125 – Lippincott)

Question 33

60.Which among these tissues depend on the hormone insulin for glucose uptake? A. muscles B. intestines C. hepatocytes D. erythrocytes

Answer 33

A. muscles Glucose Transporters: GLUT-1 is abundant in erythrocytes and brain GLUT-2 is found in liver(hepatocytes) and the β cells of the pancreas. GLUT-3 is the primary glucose transporter in neurons GLUT-4 (which is insulin-dependent) is found in muscle and adipose tissue GLUT-5 is the primary transporter for fructose (instead of glucose) in the small intestine and the testes. (P106 – Lippincott)

Question 34

61.An athlete has been training for an upcoming triathlon. His coach recommended a high carb diet after the work out to ensure a muscle glycogen storage. Activity of glycogen synthase in the resting muscles is increased by the action of: A. fasting B. glucagon C. epinephrine D. insulin

Answer 34

D. insulin The (pancreatic) β cells are the most important glucose-sensing cells in the body. Like the liver, β cells contain GLUT-2 transporters (see p. 97) and have glucokinase activity, and thus can phosphorylate glucose in amounts proportional to its actual concentration in the blood. Ingestion of glucose or a carbohydrate-rich meal leads to a rise in blood glucose, which is a signal for increased insulin secretion (as well as decreased glucagon synthesis and release). Glucose is the most important stimulus for insulin secretion. (P310 – Lippincott)

Question 35

62.Deficiency with this enzyme is associated with crampy abdominal pain and passage of loose, watery stools after significant intake of dairy product. A. sucrase B. maltase C. lactase D. galactose

Answer 35

C. Lactase Lactose Intolerance (Lactase Deficiency) – Lactose is not degraded (Not absorbed) & goes to the colon; It attracts water (Carbohydrate); Stool = Watery, Acidic, Foul-Smelling, Explosive.

Question 36

63.Pancreatic enzymes have an absolute requirement for these ions once carbohydrate digestion resumes in the lumen of the small intestines. A. sodium B. chloride C. bicarbonate D. calcium

Answer 36

C. bicarbonate Further digestion of carbohydrates by pancreatic enzymes occurs in the small intestine When the acidic stomach contents reach the small intestine, they are neutralized by bicarbonate secreted by the pancreas, and pancreatic α-amylase continues the process of starch digestion. (P86 – Lippincott)

Question 37

64.This carbohydrate is absorbed from intestine by facilitated diffusion and enters cells; converted to intermediates in glycolytic pathway; A. Sucrose B. Ribose C. Ribulose D. Fructose

Answer 37

A. Sucrose Fructose Metabolism The major source of fructose is the disaccharide sucrose, which, when cleaved in the intestine, releases equimolar amounts of fructose and glucose. (P137 – Lippincott)

Question 38

65.During the well-fed state, the liver and _________produce glycogen from excess glucose. A. Brain B. Kidney C. Muscle D. Pancreas

Answer 38

C. Muscle Fluctuation of glycogen stores Liver glycogen stores increase during the well-fed state, and are depleted during a fast. Muscle glycogen is not affected by short periods of fasting (a few days) and is only moderately decreased in prolonged fasting (weeks). Muscle glycogen is synthesized to replenish muscle stores after they have been depleted following strenuous exercise. [Note: Glycogen synthesis and degradation are cytosolic processes that go on continuously. The differences between the rates of these two processes determine the levels of stored glycogen during specific physiologic states.] (P126 – Lippincott)