Problem Based Multiple Choice Questions(solved with complete discussion)-set-1

1- A 38-year- old woman sees an advertisement for a new weight loss medication. The ad claims that the drug causes your body to burn calories without having to exercise. In theory which of the following compounds could make this claim?

a) Rotenone

b) Antimycin

c) Dinitrophenol

d) Amytal

e) Atractyloside

2-A 65-year-old man with a long history of diabetes presents to his physician after failing the driver’s license renewal eye examination. Patients with diabetes have abnormally high blood glucose levels. Glucose can enter the lens of the eye, where it can be converted to Sorbitol. Which of the following converts glucose to Sorbitol?

a) Hexokinase

b) Aldose reductase

c) Sorbitol dehydrogenase

d) Aldose oxidase

e) Glucokinase

3- A 40-year-old, obese woman presents with acute pain in the right upper quadrant of her abdomen as well as vomiting. She is diagnosed with gall stones and is placed on ursodeoxycholate, a bile salt used to inhibit the formation of cholesterol gall stones by facilitating the dissolution of cholesterol. 
Which of the following is also a bile salt?

a) HMG Co A

b) Mevalonate

c) Lanosterol

d) Squalene

e) Glycocholate

4-High carbohydrate ingestion leads to obesity, which one out of the following is the most important cause?

a) More formation of NADPH

b) More formation of fatty acids

c) More formation of glycerol

d) None of the above

e) All of the above.

5-An 18 month-old-child is left unattended while in the kitchen and ingests a small portion of rat poison found in the cupboard found under the sink. The ingredient fluoroacetate reacts with Oxaloacetate to form fluorocitrate. Which pathway of the body is inhibited by this poison?

a) Glycolysis

b) TCA cycle

c) Fatty acid oxidation

d) Fatty acid synthesis

e) HMP pathway

6- An infant is born with a high forehead, abnormal eye folds, and deformed ear lobes. He shows little muscle tone and movement. After multiple tests, he is diagnosed with Zellweger syndrome, a disorder caused by malformation of peroxisomes. 
Which of the following is expected to be high in concentration in the brain tissue of the affected individual? 

a) Ketone bodies

b) Lactate

c) Cholesterol

d) Very long-chain fatty acids

e) Branched-chain amino acids

7-A 23-year-old, boxing contender presents with an assorted metabolic disorder, most notably ketosis. During the history and physical examination, he describes his training regimen, which involves consuming a dozen raw eggs a day for protein. Raw eggs contain a protein called Avidin, with an extremely high affinity for a cofactor required for the propionyl co A carboxylase and Acetyl co A carboxylase. Name the cofactor which gets deficient by consumption of raw eggs.

a) B12

b) Vitamin C

c) Vitamin E

d) Folic acid

e) Biotin

8-A 40 -year-old woman presented with chest pain. Her blood biochemistry report did not reveal significant changes and ECG was also normal. Her family history was positive for IHD. She was kept under observation and was discharged later after a few hours. She was advised to start a low dose of Aspirin. Aspirin is considered cardioprotective since it inhibits cyclooxygenase (COX) enzyme.
COX is required for the production of which of these?

a) Thromboxane from arachidonic acid

b) Leukotrienes from Arachidonic acid

c) Phospholipids from Arachidonic acid

d) Arachidonic acid from Linoleic acid

e) Linolenic acid from Arachidonic acid

9-A 71-year-old man had a 3-week history of weakness, polyuria, intense thirst, difficulty in speaking and understanding commands, staggering walk, confusion and a weight loss of 10 kgs. For one month he took 200,000 units of vitamin D each day because he had severe osteoarthritis. His plasma calcium was 3.38 mmol/L(13.5 mg/dl)
What is the most probable diagnosis?

a) Diabetes Insipidus

b) Renal failure

c) Diabetes mellitus

d) Hypervitaminosis D

e) Hypothyroidism

10- A young infant, who was nourished with a synthetic formula, had sugar in the blood and urine. This compound gave a positive reducing sugar test but was negative when measured with glucose oxidase(specific test for detection or estimation of Glucose). Treatment of blood and urine with acid (which cleaves glycosidic bonds) did not increase the amount of reducing sugar measured. Which of the following compounds is most likely to be present in this infant’s blood and urine?

a) Glucose

b) Fructose

c) Maltose

d) Sorbitol

e) Lactose

11- A gall stone that blocked the upper part of the bile duct would cause an increase in which of the following?

a) The excretion of fats in the feces

b) Formation of chylomicrons

c) Excretion of bile salts

d) Conjugation of bile acids

e) Recycling of bile salts

12- A 3-year-old Caucasian female presents with chronic diarrhea and a failure to thrive. Stools were oily. History reveals that she was breastfed and had no problems until she was weaned. Which of the enzymes would be expected to be deficient following stimulation with secretin?

a) Cholesteryl esterase

b) Gastric lipase

c) Hormone-sensitive lipase

d) Lipoprotein lipase

e) Pancreatic lipase

13- Which of the following is least likely to contribute to the hyperglycemia associated with uncontrolled type I diabetes?

a) Decreased skeletal muscle glucose uptake

b) Decreased adipose lipogenesis

c) Increased adipose lipolysis

d) Increased hepatic gluconeogenesis

e) Increased skeletal muscle glycogenolysis

14- After excessive drinking over an extended period of time, while eating poorly, a middle-aged man is admitted to the hospital with “high output” heart failure. Which of the following enzymes is most likely inhibited?

a) Aconitase

b) Citrate synthase

c) Isocitrate dehydrogenase

d) α-Ketoglutarate dehydrogenase

e) Succinate thiokinase

15-Which of the following complications is less likely to occur in type II diabetics, as opposed to type I diabetics?

a) Retinopathy

b) Weight gain

c) Cardiovascular disease

d) hypoglycemic coma

e) Neuropathy

Answers to Multiple Choice Questions

1- The right answer is-c)  Dinitrophenol. The mechanism of action of the drug is through uncoupling of oxidative phosphorylation and Dinitrophenol is the only uncoupler in the list, rest all inhibitors of ETC except, Atractyloside which is an inhibitor of ATP/ADP transporter.

2- The right answer is b) Aldolase reductase. Hexokinase and Glucokinase are enzymes for phosphorylation of glucose in the pathway of glycolysis and sorbitol dehydrogenase is an enzyme to convert sorbitol to fructose. It is absent in most of the tissues except for liver, seminal epithelium and testicular tissue. Aldose oxidase has no role to play. Had sorbitol dehydrogenase been there in all tissues, diabetes-related complications would not have occurred, though this is not the only mechanism responsible for causing complications but a major contributor.

3- The right answer is-e)  Glycocholate. Bile salts and phospholipids keep cholesterol in the soluble form. Any condition that causes less bile salt or more cholesterol formation leads to precipitation of cholesterol. Initially, crystals are formed upon accumulation from stones. Synthetically prepared bile salt, ursodeoxycholic acid is given for the dissolution of cholesterol stones to those patients who do not want surgery or are not fit for surgery. Cholecystectomy is the ultimate cure for symptomatic gall stones. In the majority of cases, gall stones do not cause symptoms.

4- Excessive carbohydrate consumption leads to obesity The right answer is -e)
1) Excess glucose available- two main pathways of glucose utilization provide Precursors for lipogenesis
A) HMP pathway- Provides NADPH for reductive biosynthesis
 Glycolysis- Provides Acetyl co A and Glycerol-3-p
a) Excess of Pyruvate from glucose- Excess of Acetyl co A – Excessive fatty acid synthesis
b) Excess of glycerol-3-p – available from Dihydroxyacetone Phosphate
Esterification of Glycerol-3-P with fatty acids to form Triglycerides- Increased adipose mass and hence Obesity.

5 – The right answer is -b) TCA cycle

Fluoroacetate first gets converted to Fluoroacetyl COA then condenses with Oxaloacetate to get converted to Fluoro citrate to inhibit the Aconitase enzyme of the TCA cycle. It is an example of suicidal inhibition.

6-The right answer is d)-“Very long-chain fatty acids”. Very long-chain fatty acids are first trimmed in the peroxisomes till the length of C16 or C18, then they are transported to mitochondria in a conventional way through carnitine shuttle to be oxidized completely by beta-oxidation. In Zellweger syndrome the peroxisomal trimming is impaired, thus VLFA accumulates in the brain and blood of affected patients.

7- The right answer is e)- Biotin. Egg white contains Avidin, that binds with a high affinity to Biotin. Biotin is the cofactor required for conversion of Propionyl co A to D-Methyl malonyl co A and also for the conversion of Acetyl co A to Malonyl co A. Consumption of raw eggs promotes the formation of Avidin-Biotin complex causing Biotin deficiency, known as Egg white injury. The said complex is not formed if the same number of cooked eggs are ingested since cooking causes denaturation of Avidin and that loses the ability to bind with biotin.

8- a) Aspirin irreversibly acetylates cyclo-oxygenase-1 of platelets and inhibits the enzyme so that Thromboxane (TxA2) is not formed. So there is no vasoconstriction and no platelet aggregation and hence the thrombus formation is prevented.
At the same time, Aspirin also inhibits the production of Prostacyclin (PGI2) by endothelial cells, which prevents platelet aggregation and produces vasodilatation. But unlike platelets, the endothelial cells regenerate cyclo-oxygenase within a few hours. Thus the overall balance shifts towards the prevention of thrombus formation by promoting the Prostacyclin formation. Aspirin is clinically used for the prevention and management of Angina. Myocardial infarction, Stroke and Transient Ischaemic Attacks (TIA).

9- d)- It is a case of vitamin D toxicity. Usually, vitamin D toxicity results from taking excessive amounts. Because the synthesis of 1,25(OH)2D (the most active metabolite of vitamin D) is tightly regulated, vitamin D toxicity usually occurs only if excessive doses (prescription or megavitamin) are taken. Marked hypercalcemia commonly causes symptoms. Anorexia, nausea, and vomiting can develop, often followed by polyuria, polydipsia, weakness, nervousness, pruritus, and eventually renal failure. Proteinuria, urinary casts, azotemia, and metastatic calcifications (particularly in the kidneys) can develop.
Diagnosis is typically based on elevated blood levels of 25(OH)D. Treatment consists of stopping vitamin D, restricting dietary Ca, restoring intravascular volume deficits, and, if toxicity is severe, giving corticosteroids or bisphosphonates.

10 – The right answer is b)- fructose. Glucose cannot be there since a specific test is negative. Sorbitol is non-reactive to reduction test. Maltose and lactose would have caused an increase in the amount of reducing sugar upon acid hydrolysis. Hence it is fructose which is reducing in nature nut non-reactive to glucose oxidase.

11- The right answer is-a)  excretion of excess fats in the feces, In this situation, bile salts cannot enter the digestive tract. therefore recycling and excretion of bile salts, digestion of fats, and formation of chylomicrons are decreased. As a consequence fat in the feces is increased (Steatorrhea).

12- e),  Neither hormone-sensitive lipase nor lipoprotein lipase is a digestive enzyme. The patient’s symptoms are consistent with an inability to absorb triglycerides, which would eliminate cholesteryl esterase from consideration. Since the patient did not have any problem while being breastfed, then the most likely enzyme to be deficient is pancreatic lipase, since gastric lipase is most active on short-chain triglycerides, such as those that are found in breast milk.

13- e)- Unlike the liver, skeletal muscle cannot export glucose into the circulation.
Once glucose enters the myocyte, it is destined for use by that cell. Thus, intramyocellular glycogen is used as a fuel source by skeletal muscle and therefore cannot contribute to the hyperglycemia observed in uncontrolled type I diabetes. In contrast, decreased insulin-mediated glucose utilization by skeletal muscle and adipose will contribute to hyperglycemia, as will decreased insulin-mediated suppression of hepatic glucose output. Decreased insulin-mediated suppression of lipolysis will indirectly contribute to hyperglycemia, by providing alternative, nonglucose, fuels (fatty acids and ketone bodies) or organs such as skeletal muscle and the liver.

14- d)- This patient has exhibited symptoms of beri-beri heart disease, which is a result of a nutritional deficiency in vitamin B1 (thiamine). The active form of the vitamin, thiamine pyrophosphate, is a required cofactor for α-ketoglutarate dehydrogenase.

15- d)-  Hypoglycemia is a common complication associated with over-supplementation of type I diabetics with insulin. This is less common in type II diabetics because insulin therapy generally occurs only in the later stages of the pathogenesis of this disease. Retinopathy, cardiovascular disease, and neuropathy are common complications associated with both forms of diabetes mellitus. In contrast to type I diabetics, type II diabetics tend to be overweight. Whether weight gain is a cause or consequence of disease progression is under the current debate.