Biochemistry-Problem-based multiple choice questions

1)- Several complexes in the electron transport chain contain non-heme iron. The iron in these complexes is bound tightly to which of the following amino acids?

a) Serine

b) Tyrosine

c) Cysteine

d) Methionine

e) Glutamine

2)- A 27 –year-old female with epilepsy has been taking Phenytoin to control her seizures. She is pregnant and considering the risk of potential bleeding episodes in the infant. Her physician is considering changing her medicine. What biochemical activity might be deficient in the baby if her medication is continued as such?

a) Hydroxylation of proline

b) Gamma carboxylation of glutamic acid residues

c) Glucuronidation of bilirubin

d) Oxidation of lysine

e) Oxidation of glutathione.

3)- A 75-year-old female is seen in the emergency room with a fractured arm. Physical examination reveals multiple bruises, perifollicular hemorrhages, and bleeding gums. Her diet consisted mainly of plain buns, pasta, rolls, and coffee. Laboratory result indicates Microcytic hypochromic anemia. Which of the following enzymes should be less active than normal in this patient?

a) Glutathione peroxidase

b) Prolyl hydroxylase

c) Gamma Glutamyl transferase

d) ALA synthase

e) Glutathione reductase

4)- An 8-year-old child with IDDM (Insulin-dependent diabetes mellitus) has been brought to the emergency semi-consciously. History reveals that he had a flu-like episode 8 days back. His breathing is rapid, and his breath has a fruity odor. His blood glucose is 345 mg/dl. The physician has started with I/V fluids, Insulin, and potassium chloride. Insulin under such conditions would rapidly stimulate which of the following processes-

a) Gluconeogenesis in liver

b) Glycogenolysis in liver

c) Uptake of glucose in peripheral cells

d) Lipolysis in adipose tissue

e) Ketone body utilization in brain cells.

5)- A 55-year-old chronic alcoholic was brought to the emergency by his friends. During their nighttime gathering in the local bar, he fell unconscious, and they could not revive him. The attending physician ordered I/V Glucose and an injection of Thiamine. The patient was well oriented and alert the following day; his vital signs were stable, his blood glucose was normal, and he was discharged from the hospital. Which of the following enzymes is Thiamine dependent and vital for glucose oxidation in the brain?

a) Transketolase

b) Transaldolase

c) Transaminase

d) Pyruvate dehydrogenase complex

e) Alpha keto acid dehydrogenase complex

6)- During acute myocardial infarction, the oxygen supply to an area of the heart is reduced, forcing the cardiac muscle cells to switch to anaerobic oxidation. Under these conditions, the activity of which of the following enzymes is increased by the increasing concentration of AMP?

a) Phospho fructokinase-1

b) Pyruvate kinase

c) Citrate synthase

d) Lactate dehydrogenase

e) Succinate dehydrogenase

7)- A 50- year-old male is seen in the emergency with a severe headache. His blood pressure is 210/130 mm Hg. Evidence of retinal hemorrhage and epistaxis is also there. He has been given an infusion of nitroprusside. Which of the following enzymes is directly affected by the active metabolite of this drug?

a) Phospholipase A2

b) Phospholipase C

c) Guanylate cyclase

d) Phosphodiesterase

e)  Adenylate cyclase

8) A 16-month-old girl was found to have ingested approximately 30 mL of an acetonitrile-based cosmetic nail remover when she vomited 15 minutes post-ingestion. The poison control center was contacted, but no treatment was recommended because it was confused with an acetone-based nail polish remover. The child was put to bed at her normal time, which was 2 hours post-ingestion. Respiratory distress developed sometime after the child was put to bed, and she was found dead the following day.

Inhibition of which of the following enzymes was the most likely cause of this child’s death?

a) Cytochrome c reductase

b) Cytochrome oxidase

c) Coenzyme Q reductase

d) NADH dehydrogenase

e) Succinate dehydrogenase

9)- Excess nitroprusside sometimes causes cyanide toxicity and is treated by giving thiosulfate. Which complex associated with electron transport chain or oxidative phosphorylation gets inhibited by the toxic metabolic product of nitroprusside?

a) ATP synthase complex

b) Succinate dehydrogenase complex

c) ADP/ATP transporter

d) NADH dehydrogenase complex

e) Cytochrome a-a3 oxidase

10)-A patient has been exposed to a toxic compound that increases the mitochondrial membrane permeability for protons. Which of the following will not be observed in the liver cells?

a) Increased glycolysis

b) Increased activity of ATP synthase complex

c) Increased concentration of ADP

d) Increased activity of PFK-1

e) Increased activity of pyruvate kinase

11) – A 56-year-old man with a history of genetic disease underwent hip replacement surgery for arthritis. During surgery, black stains were observed in the cartilage. These stains are usually observed in patients suffering from Ochronosis, a condition initially characterized by the darkening of urine upon standing (Alkaptonuria). There is a deficiency of Homogentisic acid oxidase in this condition. Which of the following vitamins acts as a coenzyme for the above-said enzyme?

a) Vitamin B12

b) Folic acid

c) Ascorbic acid

d) Niacin

e) Riboflavin

12)  In a  patient with Abetalipoproteinemia,  abnormal red blood cells (Acanthocytes- thorny-looking cells) are observed. There is a defective synthesis of Apo B protein in this condition. Which of the following would have impaired absorption, the deficiency of which leads to impaired membrane formation in this condition?

a) Folic acid

b) Ascorbic acid

c) Palmitic acid

d) Arachidonic acid

e) Linolenic acid

13) Failure of down-regulation of extrahepatic receptors for oxidized LDL is mainly responsible for the formation of foam cells and for triggering the process of atherosclerosis. This process can be prevented by timely supplementation of antioxidants. Which of the following should be considered the best choice to be considered as an antioxidant?

a) Vitamin B6

b) Vitamin K

c) Vitamin D

d) Vitamin E

e) Folic acid

14)- A factory worker has been on a hunger strike for the last three days. Beta oxidation is presumed to be highly active under such conditions. What would be the expected fate of mitochondrial pyruvate?

a)  Oxidatively decarboxylated to form Acetyl co A to be used in the TCA cycle

b) Carboxylated to Phosphoenol pyruvate  to be used for gluconeogenesis

c) Reduced to lactate to be used for gluconeogenesis

d) Oxidatively decarboxylated to form Acetyl co A to be used for ketogenesis

e) Carboxylated to Oxaloacetate to be used for gluconeogenesis.

15) -In the fed state, after a very heavy meal, there is active lipogenesis in the adipose tissue. Glycolysis must go on at the same pace to provide which of the following intermediate from glycolysis is required for fat storage?

a) Acetyl co A

b) Pyruvate

c) Glucose-6-P

d) Glycerol

e) Dihydroxy acetone phosphate

16) A child is diagnosed with congenital deficiency of medium chain Acyl co A dehydrogenase. Which of the following biochemical finding would be observed in the fasting state?

a) Hyperglycemia

b) Low blood lactate level

c) Ketosis

d) Dicarboxylic acidosis

e) Alkalosis

17)  A 6-year-old child has been brought with impairment of vision. He is diagnosed with Galactosemia.  Which enzyme is responsible for causing premature cataracts in such affected children?

a) Sorbitol dehydrogenase

b) Aldose reductase

c) Galactokinase

d) Galactose-1-P- Uridyl transferase

e) Aldolase -B

Key to Answers-

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