Monday, October 22, 2012

Multiple choice Questions- Pentose phosphate pathway


1) Glucose breakdown in certain mammalian and bacterial cells can occur by mechanisms other than classic glycolysis. In most of these, glucose 6-phosphate is oxidized to 6- phosphogluconate, which is then further metabolized by:

a) an aldolase-type split to form glyceric acid and glyceraldehyde 3-phosphate.

b) an aldolase-type split to form glycolic acid and erythrose 4-phosphate.

c) conversion to 1,6-bisphosphogluconate.

d) decarboxylation to produce keto- and aldopentoses

e) oxidation to a six-carbon dicarboxylic acid.

2) Which of the following enzymes acts in the pentose phosphate pathway?

a) 6-phosphogluconate dehydrogenase

b) Aldolase

c) Glycogen phosphorylase

d) Phosphofructokinase-1

e) Pyruvate kinase

3) The oxidation of 3 mol of glucose by the pentose phosphate pathway may result in the production of:

a) 2 mol of pentose, 4 mol of NADPH, and 8 mol of CO2.

b) 3 mol of pentose, 4 mol of NADPH, and 3 mol of CO2.

c) 3 mol of pentose, 6 mol of NADPH, and 3 mol of CO2.

d) 4 mol of pentose, 3 mol of NADPH, and 3 mol of CO2.

e) 4 mol of pentose, 6 mol of NADPH, and 6 mol of CO2.

4) In a tissue that metabolizes glucose via the pentose phosphate pathway, C-1 of glucose would be expected to end up principally in:

a) Carbon dioxide

b) Glycogen

c) Phosphoglycerate

d) Pyruvate

e) Ribulose 5-phosphate

5) The main function of the pentose phosphate pathway is to:

a) give the cell an alternative pathway should glycolysis fail

b) provide a mechanism for the utilization of the carbon skeletons of excess amino acids

c) supply energy

d) supply NADH

e) supply Pentoses and NADPH

6) Which of the following statements about the pentose phosphate pathway is correct?

a) It generates 38 mol of ATP per mole of glucose consumed.

b) It generates 6 moles of CO2 for each mole of glucose consumed

c) It is a reductive pathway; it consumes NADH.

d) It is present in plants, but not in animals.

e) It provides precursors for the synthesis of nucleotides.

7) The reactions of the pentose phosphate pathway using glucose-6 phosphate as the initial substrate are best described by which of the following statements ?

a) They produce 2 moles of NADPH for each mole of CO2 released.

b) They generate 2 moles of adenosine triphosphate per mole of glucose-6-phosphate metabolized to ribulose-5 phosphate.

c) They occur in the matrix of mitochondria.

d) They are not required for the production of NADPH in the mature red blood cells

e) They are required for the  metabolism of glucose in the muscles.

8) In the pentose phosphate pathway, the major products are which of the followings ?

a) Ribulose and ATP

b) Ribulose and NADPH

c) Ribose and NADH

d) Ribose and NAD+

e) Xylulose and ATP

9) Which of the following statements about the oxidative section of the pentose phosphate pathway is correct?

a) The pentose phosphate pathway generates NADH.

b) The pentose phosphate pathway oxidizes NADPH to NADP+

c) The rate-limiting reaction of the pentose phosphate pathway is catalyzed by glucose-6-phosphatase.

d) The pathway supplies ribose-5-phosphate and NADPH in the quantities the cells requires.

e) The pathway is highly active in the fasting state.

10) Which of the following statements about the nonoxidative section of the pentose phosphate pathway is correct?

a) The nonoxidative reactions of the pentose phosphate pathway are not reversible.

b) Transketolase is an enzyme that transfers three-carbon units in the pentose phosphate pathway

c) Transaldolase is an enzyme that transfers two-carbon units in the pentose phosphate pathway

d) Pentoses can provide glycolytic intermediates in this phase of HMP pathway

e) Pentoses can be metabolized to provide NADPH in this phase of HMP pathway.

11) Which of the following statements about the use of the NADPH generated from the pentose phosphate pathway is not correct?

a) NADPH generated from the pentose phosphate pathway is used for steroid synthesis.

b) NADPH generated from the pentose phosphate pathway is used for the regeneration of glutathione to its reduced state.

c) NADPH generated from the pentose phosphate pathway is used for the synthesis of fatty acids

d) NADPH generated from the pentose phosphate pathway can be oxidized in the electron transport chain to provide 38 ATPs

e) NADPH generated from the pentose phosphate pathway is used for the Macrophageal functions.

12) A 19- year-old, African-American male military recruit is about to be sent to Iraq on his assignment. In preparation for his tour of duty, he is given a prophylactic dose of primaquine to prevent malaria. Several days after he develops fatigue and hemolytic anemia. Which of the following enzymes is likely deficient ?

a) Fructokinase

b) Aldolase B

c) Glucose-6-P dehydrogenase

d) Galactokinase

e) Galactosyl Transferase.

13) A 50 -year-old alcoholic male presents with pain, numbness, tingling and weakness in his feet. He is diagnosed with thiamine deficiency. Thiamine and ATP condense together to form   thiamine pyrophosphate, a cofactor important for the enzymes that catalyze oxidative decarboxylation of (α-keto acids) in the TCA cycle and also at one of the steps in pentose phosphate pathway, which out of the following enzymes requires TPP as a coenzyme ?

a) Glucose-6-P dehydrogenase

b) Transaldolase

c) Transketolase

d) 6-P-Gluconate dehydrogenase

e)  Gluconolactone hydrolase.

14) The key regulatory enzyme of HMP pathway is-

a) Glucose-6-P dehydrogenase

b) Transaldolase

c) Transketolase

d) 6-P-Gluconate dehydrogenase

e)  Gluconolactone hydrolase.

15) Xylulose 5-phosphate can be formed from Ribulose 5-phosphate by the action of-

a) Glucose-6-P dehydrogenase

b) Transaldolase

c) Transketolase

d) Phosphopentose epimerase

e)Phosphopentose isomerase.

16)-The pentose phosphate pathway is active in liver, adipose tissue, adrenal cortex, thyroid, erythrocytes, testis, and lactating mammary gland. Why is the pathway less active in skeletal muscle?

a) Muscle tissue contains very small amount of dehydrogenases

b) Muscle tissues do not require NADPH

c) Pentoses the major product of this pathway are not required by muscle tissue

d) Muscle tissue contains very small amount of enzymes of non oxidative phase

e) All of the above.

17) In rapidly dividing cancer cells the need for large amount of ribose is fulfilled by-

a) Highly active Glucose-6-P dehydrogenase

b) Highly active Transaldolase

c) Highly active Transketolase

d) Highly active 6-P-Gluconate dehydrogenase

e) Reversal of non oxidative phase using glycolytic intermediates.



 Answers-        1)-d                2)-a                  3)-c                  4)-a                  5)-e                

                        6)-b                 7)-a                  8)-b                 9)-d                 10)-d

                        11)-d               12)-c                13)-c                14)-a                15)-d

                        16)-a                17)-e



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