Monday, October 22, 2012

Gluconeogenesis- Multiple Choice Questions


1)  A 4-month-old boy is being evaluated for seizures, psychomotor retardation, and hypotonia. Work up reveals elevated serum levels of lactate, alanine, pyruvate and keto acids. Based on the clinical presentation,pyruvate carboxylase activity is measured using fibroblasts from a skin biopsy and is found to be markedly decreased. This enzyme is normally used to directly synthesize which of the following molecules ?

a) Pyruvate

b) Oxaloacetate

c) Malate

d) Acetyl co A

e) α- Keto glutarate

2) A 34-year-old woman presents with central obesity, relatively thin extremities and purple stria on her abdomen. Further work up reveals an excessive serum cortisol level and a blood sugar level of 258 mg/dl. Which of the following is the most likely cause of her hyperglycemia ?

a) Excessive consumption of processed carbohydrates

b) A pancreatic adenoma secreting  ACTH and glucagon

c) Cortisol induced inhibition of insulin

d) Glucorticoids cause induction of Phosphoenolpyruvate carboxy kinase gene

e) Increased gluconeogenesis due to increased provision of substrates through fatty acid oxidation.

3) A 56-year-old, obese man complains of polydipsia, polyuria and fatigue. A glucose tolerance test confirms the diagnosis of diabetes. He is placed on Metformin, which works by which of the following mechanisms ?

a) Inhibiting hepatic gluconeogenesis

b) Increasing glucagon level

c) Increasing cellular responsiveness to circulating insulin

d) Stimulating the release or preformed insulin

e) Replacing the need for endogenous insulin

4) An enzyme used in both glycolysis and gluconeogenesis is:

a) 3-phosphoglycerate kinase.

b) Glucose 6-phosphatase

c) Hexokinase

d) Phosphofructokinase-1

e) Pyruvate kinase

5) Which one of the following statements about gluconeogenesis is false?

a) For starting materials, it can use carbon skeletons derived from certain amino acids.

b) It consists entirely of the reactions of glycolysis, operating in the reverse direction.

c) It employs the enzyme glucose 6-phosphatase.

d) It is one of the ways that mammals maintain normal blood glucose levels between meals.

e) It requires metabolic energy (ATP or GTP).

6) All of the following enzymes involved in the flow of carbon from glucose to lactate (glycolysis) are

also involved in the reversal of this flow (gluconeogenesis) except:

a) 3-phosphoglycerate kinase.

b) Aldolase

c) Enolase

d) Phosphofructokinase-1

e) Phosphohexoseisomerase

7) In humans, gluconeogenesis:

a) can result in the conversion of protein into blood glucose.

b) helps to reduce blood glucose after a carbohydrate-rich meal.

c) is activated by the hormone insulin

d) is essential in the conversion of fatty acids to glucose.

e) requires the enzyme hexokinase.

8) Which of the following substrates cannot contribute to net gluconeogenesis in mammalian liver?

a) Alanine

b) Glutamate

c) Palmitate

d) Pyruvate

e) α-Keto glutarate.

9) A 6-year-old boy begins playing soccer in a community league. After his first game of the year, he is brought to see his pediatrician because of his severe muscle cramps and blood in urine. He is subsequently found to be having deficiency of lactate dehydrogenase. This enzyme is important in which of the following conversions ?

a) Pyruvate to Acetyl co A

b) Pyruvate to Oxaloacetate

c) Pyruvate to Alanine

d) Pyruvate to Phosphoenol pyruvate

e) Pyruvate to lactate

10) A new-born infant is found to be having persistent hypoglycemia, despite decreased feeding intervals. The child is also irritable with a moderate degree of hepatomegaly. He is found to have a normal level of muscle fructose 1,6 bisphosphatase but decreased level of liver isoform. Which of the following statement is true of fructose 1,6 bisphosphatase?

a) It is induced by Adenosine mono phosphate (AMP)

b) It is induced by Insulin

c) It is inhibited by Fructose 2,6 bisphosphate

d) It is induced in the fed state

e) It is inhibited during fasting.

11) A 14-year-old  high school girl who is extremely conscious about her appearance has gone a full day fasting to fit in to a dress she intentionally brought a size smaller than her actual size for a dance party. Which of the following organs/tissues contributes to the glucose  that is being synthesized through gluconeogenesis ?

a) Spleen

b) Red blood cells

c) Skeletal muscle

d) Liver

e) Brain

12) An 8 -year-old boy presents with frequent episodes of weakness, accompanied by sweating and feelings of dizziness. Physical examination is remarkable for palpably enlarged liver and kidneys. Blood biochemistry reveals lactic acidemia. The patient is diagnosed with deficiency  of glucose-6-phosphatase, which is normally only expressed in-

a) Liver and muscle

b) Liver and brain

c) Erythrocytes

d) Liver and adipose tissues

e) Liver and kidney.

13)  A 32-year-old body builder has decided to go on a diet consisting of egg whites to ensure only proteins for muscle growth. After a few weeks he experiences  decreased energy and is found to be hypoglycemic. A nutritionist tells the patient that he most likely has the deficiency of vitamin Biotin. Which of the following enzymes is unable to catalyze its step in synthesizing glucose from pyruvate?

a) Pyruvate carboxylase

b) Phospho enol pyruvate carboxy kinase

c) Glucose-6-phosphatase

d) Fr 1,6 bisphosphatase

e) Phosphoglycerate kinase.

14) In an individual at rest, who has fasted for 12 hours, which of the following occurs ?

a) Gluconeogenesis is the major process by which blood glucose is maintained

b) Liver glycogen stores are depleted

c) Glycogen synthase is activated in liver

d) Adenylate cyclase is inactivated in liver

e) Phosphorylase, pyruvate kinase and glycogen synthase are phosphorylated in liver.

15) Which of the following is a common intermediate in the conversion of glycerol and lactate to glucose ?

a) Pyruvate

b) Oxaloacetate

c) Malate

d) Glucose-6-phosphate

e) Phosphoenolpyruvate.

16) In the conversion of pyruvate to glucose during gluconeogenesis,

a) Biotin is required

b) CO2 added in one reaction, appears in the final product

c) Energy is used up in the form of GTP

d) All the reactions take place in the cytosol

e) PDH is the allosteric enzyme used.

17) Which of the following glycolytic enzymes is used in gluconeogenesis ?

a) Glucokinase

b) Phosphofructokinase-1

c) Aldolase B

d) Phosphoglycerate kinase

e) Pyruvate kinase.

18) The conversion of pyruvate to fructose 1,6 bisphosphate by the gluconeogenic pathway involves which of the followings ?

a) Requires lactate dehydrogenase

b) Requires hexokinase

c) Produces 2 ATP and 2GTP

d) Requires 4 ATP and 2 GTP

e) Acetyl co A is not required to activate this pathway.

19) A high ratio of insulin to glucagon can:

a) Promote gluconeogenesis

b) Promote glycogenolysis

c) Found in Type 1 Diabetes Mellitus

d) Occurs during fasting state

e) Promotes synthesis of  Glycogen

20) Which of the followings is a precursor for gluconeogenesis ?

a) Glycogen

b) Glycerol

c) Glucagon

d) Galactose

e) Glucose-1- P.



Answers-  1)-b ,  2)-d,  3)-a,  4)-a,  5)-b,  6)-d,  7)-a,  8)-c,  9)-e,  10)-c,  11)-d,  12)-e,  13)-a,  14)-e,  15)-d,  16)-a ,17)-d,  18)-d,

19)-e,  20)-b.



------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com ------------------------------------------
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