Monday, October 22, 2012

Multiple Choice Questions- Carbohydrate metabolism

Q.1 – Which of the following substrates derived from adipose tissues contributes to net Gluconeogenesis in mammalian liver?

a) Alanine

b) Glutamate

c) Glycerol

d) Pyruvate                                                                                                               (    c     )

Q.2 – Which of the following statements is incorrect?

a) Aerobically, oxidative decarboxylation of pyruvate forms acetate that enters the citric acid cycle.

b) In anaerobic muscle, pyruvate is converted to lactate.

c) Reduction of pyruvate to lactate generates a coenzyme essential for Glycolysis.

d) Under anaerobic conditions pyruvate does not form because Glycolysis does not occur.

                                                                                                                                                         (     d    )

Q.3- The steps of Glycolysis between glyceraldehyde 3-phosphate and 3-phosphoglycerate involve all of the following except:

a) ATP synthesis.

b) Catalysis by phosphoglycerate kinase.

c) Oxidation of NADH to NAD+.

d) The formation of 1, 3- bisphosphoglycerate.                                                    (    c     )

Q.4 – 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 8mol of CO2.

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

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

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

Q.5 – How many ATP molecules can be derived from each molecule of acetyl CoA that enters the Krebs’ Cycle?

a) 6

b) 12

c) 18

d) 38                                                                                                                                       (     b    )

Q.6 – All of the following vitamins except one participate in the TCA cycle-

a)Pantothenic acid

b)Lipoic acid

c) Folic acid

d)Riboflavin                                                                                                                        (    c     )

Q.7 – Why Phosphofructokinase rather than hexokinase is the pacemaker of Glycolysis?

a) Glucose 6-phosphate is not solely a glycolytic intermediate

b) Hexokinase has low km for glucose

c) Hexokinase is inhibited by feed back inhibition

d) None of the above                                                                                                       (     a    )

Q.8 - All are correct about pyruvate dehydrogenase complex except one-

a)The formation of acetyl CoA from pyruvate is an irreversible step

b) Pyruvate dehydrogenase is switched off when Acetyl co A is in excess

c)Phosphorylation switches off the activity of the complex.

d) Pyruvate as well as ADP (a signal of low energy charge) inhibits the complex.    (     d    )

Q.9-Cellular isozymes of pyruvate kinase are allosterically inhibited by:

a) High concentrations of AMP.

b) High concentrations of ATP.

c) High concentrations ofFr1,6 bisphosphate.

d) Low concentrations of acetyl-CoA.                                                                       (    b     )

Q.10 – Which of the followings is not an intermediate of the citric acid cycle?

a) Acetoacetate

b) Citrate

c) Oxalosuccinate

d) Succinyl-CoA                                                                                                                 (    a     )

Q.11 - In an anaerobic system that is metabolizing glucose as a substrate, which of the following compounds would you expect to increase in concentration following the addition of fluoride?

 a) 2-phosphoglycerate

b) Glucose

c) Phosphoenolpyruvate

d) Pyruvate                                                                                                                            (   a    )

Q.12 – Which of the following is a coenzyme  in the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase?

a) ATP

b) Cu2+

c) Heme

d) NAD+                                                                                                                               (     d    )

Q.13 - An enzyme used in both glycolysis and gluconeogenesis is:

a) 3-phosphoglycerate kinase.

b)Glucose 6-phosphatase.

C) Hexokinase.

d)Phosphofructokinase-1.                                                                                            (     a    )

Q.14 – Which of the following statements about the pentose phosphate pathway is incorrect?

 a) It generates 36 mol of ATP per mole of glucose consumed.

b) It generates 6 moles of CO2for each mole of glucose consumed

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

d) It provides precursors for the synthesis of nucleotides                                 (     c    )

Q.15 – Which of the following enzymes catalyzes a reaction that involves a decarboxylation reaction?

 a)Pyruvate dehydrogenase

b) Isocitrate dehydrogenase

c) α-keto glutarate dehydrogenase

d all of the above                                                                                                              (     d    )

Q.16 -Anaplerotic reactions are those that result in replenishing intermediates in the TCA cycle. Which of the following enzymes catalyzes an Anaplerotic reaction?

a)  Malate dehydrogenase

b) Pyruvate carboxylase

c) Pyruvate kinase

d). Citrate synthase                                                                                                         (      b   )

Q.17- Which statement BEST describes the fate of Propionyl-CoA in mammalian systems?

a) Propionyl-CoA is metabolized via are action sequence that involves vitamin B12 and biotin.

b) Propionyl-CoA is converted to acetyl CoA.

c) Propionyl-CoA and acetyl CoA condense to form a 5 carbon precursor of a TCA cycle intermediate.

d) Propionyl-CoA is oxidized to Malonate and CoA                                              (      a   )

Q.18 – It is very important to feed the baby very soon after birth, because during the first few hours after birth the enzyme Phosphoenolpyruvate carboxykinase is present in very low amounts, and this fact compromises:

a) Gluconeogenesis

b) Glucose phosphorylation

c) Glycogenesis

d) Glycogenolysis                                                                                                                (    a     )

Q.19 – The citric acid cycle is inhibited by which of the following?

 a) Fluoroacetate

b) Aerobic conditions

c) Malic acid

d) Fluorouracil                                                                                                                    (     a    )

Q.20 – Which of the following enzymes is associated with Glycogen synthesis?

a) Amylo- (1, 4->1,6) – transglycosylase

b) Phosphorylase

c) Amylo-1,6-glucosidase

d) Glucose-6- phosphatase                                                                                            (       a  )

Q.21 – A medical student developed hemolytic anemia after taking the oxidizing Antimalarial drug primaquine. This severe reaction is most likely due to

 a) Glucose-6- phosphate dehydrogenase deficiency

b) Concomitant Scurvy

c) Diabetes

d) Glycogen phosphorylase deficiency                                                                     (    a     )

Q.22- Which of the following explains why individuals with hyperlipidemia should minimize their intake of sucrose and high fructose syrup?

 a) Fructose metabolism is faster than glucose

b) After initial modification fructose is cleaved by a specific Enolase

c) Fructose is ultimately converted to galactose

d) Fructose can be phosphorylated by hexokinase in adipose cells                   (    a     )

Q.23-The major glycolytic product produced under normal circumstances by erythrocytes required for unloading of oxygen to the peripheral tissues is

 a) 2,3bisphosphoglycerate

b) 1,3bisphosphoglycerate

d)Lactate                                                                                                                                       (     a    )

c) Pyruvate

Q.24 – Poorly perfused areas exposed to chronic hypoxia have decreased metabolic energy for tissue maintenance and repair an important reason for this is-

 a)  Increased hexokinase activity owing to increased oxidative phosphorylation

b) Decreased ATP production and increased glucose utilization due to an aerobic mode of glycolysis

c) Increased glucose utilization by HMP pathway on changing from anaerobic to aerobic glycolysis

d) Decreased respiratory quotient on changing from carbohydrates to fats as the major fuel                                                                                                                                                              (    b     )

Q.25 – Asians and Native Americans may flush and feel ill after drinking a small amount of ethanol in alcoholic beverages. This reaction is due to genetic variation in an enzyme that metabolizes the liver metabolite of alcohol, which is-

 a) Methanol

b) Acetone

c) Acetaldehyde

d) Glycerol                                                                                                                                    (    c     )

Q.26 – Which one of the following enzymes catalyzes the phosphorylation of the substrate with the use of inorganic phosphate-?

a) Hexokinase

b) Phospho fructokinase

c) Glyceraldehyde-3-phosphate dehydrogenase

d) Phospho glycerate kinase                                                                                                  (     c    )

------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123, ------------------------------------------

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