Biological oxidation and Electron Transport Chain (Mcqs) – part-2

1. Dehydrogenases catalyze the transfer of hydrogen from one substrate to another in a coupled oxidation-reduction reaction.These dehydrogenases are specific for their substrates but often utilize common coenzymes or hydrogen carriers, e.g. NAD+. Which out of the following is not niacin ( NAD+) dependent dehydrogenase?

a) Pyruvate dehydrogenase

b) Glycerol-3-P dehydrogenase( Mitochondrial )

c) Glyceraldehyde-3-P dehydrogenase

d) Lactate dehydrogenase

e) Alpha-ketoglutarate dehydrogenase

2. The cytochromes are iron-containing hemoproteins in which the iron atom oscillates between Fe³⁺ and Fe²⁺ during oxidation and reduction. Most of the cytochromes of the electron transport chain are classified as dehydrogenases. Which out of the following cytochromes is not a dehydrogenase?

a) NADH-Q oxidoreductase (Complex I)

b) Q-cytochrome c oxidoreductase (Complex III)

c) cytochrome c oxidase (Complex IV)

d) Succinate Q reductase (Complex II)

e) cytochrome c

3. A 2-year – old child has been brought to pediatric OPD with the complaint of the passage of black colored urine. A probable diagnosis of Alkaptonuria has been made. Alkaptonuria is a congenital disorder of deficiency of Homogentisic acid oxidase. Homogentisic acid oxidase is an enzyme of tyrosine metabolic pathway and functionally it is –

a) A dehydrogenase

b) An oxidase

c) Monooxygenase

d) Dioxygenase

e) Hydroperoxidase

4. A 23 -year – old male has been brought to medical OPD with jaundice and passage of dark-colored urine. History reveals that he took antibiotic sulphonamides for a sore throat and ever since he developed the symptoms. There is a history of previous such episodes also. A probable diagnosis of Glucose-6-P dehydrogenase deficiency has been made. NADPH  produced from the activity of this enzyme is required for the reductive processes in the body. The reduction of oxidized glutathione is one such process. G-SH (Reduced glutathione) is required for the activity of a selenium-containing peroxidase, an enzyme required for the maintenance of the integrity of the red blood cell membrane. The reduced activity of this enzyme is responsible for hemolytic anemia in such patients. Which of the following is not a product of this enzyme-catalyzed reaction?

a) Hydrogen peroxide

b) Water

c) Oxidized substrate

d) NADP⁺

e) Oxidized glutathione

5. A chronic alcoholic has been brought to a medical emergency. Blood biochemistry reveals lactic acidosis. The deficiency of the pyruvate dehydrogenase complex is suspected. Pyruvate dehydrogenase complex (PDH complex) is a multienzyme complex, that requires, thiamine, Pantothenic acid, lipoic acid, riboflavin, and niacin for its action and catalyzes the oxidative decarboxylation of pyruvate to form acetyl co A. During this process of oxidation what is the expected P:O ratio?

a) 3:1

b) 6:1

c) 4:1

d) 12:1

e) 38 :1

6. For each acetyl Co-A oxidized by the citric acid cycle, what is the energy gain by substrate-level phosphorylation?

a) 2 ATP

b) 4 ATP

c) 6 ATP

d) 1 ATP

e) Zero ATP

7.Which of the following enzymes catalyzes a reaction with the resultant  P:O ratio of 2:1?

a) Glycerol-3-P-dehydrogenase (Cytosolic)

b) Succinate dehydrogenase

c) Malate dehydrogenase

d) Lactate dehydrogenase

e) Glucose-6-P dehydrogenase

8. Which of the following compounds inhibits oxidative phosphorylation by inhibiting the transporter of ADP into and ATP out of the mitochondrion?

a) Malonate

b) Oxamate

c) Atractyloside

d) Barbiturates

e) Cyanide

9. The energy of oxidation is initially trapped as a high-energy phosphate compound and then used to form ATP. Which of the following intermediates of glycolysis is a high energy compound?

a) Fructose-6-P

b) Glyceraldehyde-3-P

c) Fructose-1,6 bisphosphate

d) Glucose-6-P

e) Phosphoenol pyruvate

10. ATP is a nucleotide consisting of adenine, a ribose, and a triphosphate unit. The active form of ATP is usually a complex of ATP with Mg²⁺ or Mn2+. ATP is an energy-rich molecule because its triphosphate unit contains two phosphoanhydride bonds. A large amount of free energy of the amount ——– approximately is liberated when ATP is hydrolyzed to adenosine diphosphate (ADP) and orthophosphate (Pi).

a) 12.3 kcal/mol

b) 10.9 kcal/mol

c) 6.8 kcal/mol

d) 7.3 kcal/mol

e) 8.3 kcal/mol

11.  Which of the components of the electron transport chain does not contain the Iron-sulfur center?

a) NADH dehydrogenase complex

b) Cytochrome a-a3 oxidase

c) Succinate dehydrogenase

d) Cytochrome bc₁-c reductase

12. Aspirin in a high dosage produces hyperthermia, despite the fact that it is itself an antipyretic agent. The reason for this effect is-

a) Aspirin affects hypothalamic functions

b) It uncouples oxidative phosphorylation

c) It stimulates metabolism

d) It is itself metabolized to high energy compound

e) All of the above.

13. Choose the incorrect statement out of the following about complete oxidation of glucose in the presence of oxygen-

a) In RBC s nearly 90% of the energy is obtained via oxidative phosphorylation

b) 1,3 Bisphosphoglycerate is a high energy compound

c) The conversion of phosphoenolpyruvate to pyruvate  yields 2 ATP

d) Net energy output in skeletal muscle is 36 ATP

e) 10 % of the total energy is obtained by substrate-level phosphorylation in most tissues

14. Choose the correct statement out of the following about Iron-Sulfur centers-

a) Iron-sulfur proteins (non-heme iron proteins, Fe-S)  are found in Complexes IV

b) These may contain five  iron atoms linked to inorganic sulfur atoms

c) Iron may be linked through  cysteine-SH groups to the protein

d) The Fe-S take part in two-electrons transfer reactions

e) The Fe atom always remains in the reduced form ( Fe²⁺⁾ .

Key to answers- 1)-b , 2)-c, 3)-  d, 4)- a, 5- b, 6)-a, 7)-b, 8)-c, 9)-e,10)-d, 11)-b, 12-b, 13)-a, 14)-c.