Practice questions-set-6

1. A 24-year-old female presents with complaints of intestinal bloating, gas, cramps, and diarrhea following a meal including dairy products. A lactose-tolerance test confirms that she has a deficiency of lactase. Which of the following dairy products could you recommend that would be least likely to cause her difficulties in the future?

a) Condensed milk

b) Cottage cheese

c) Ice cream

d) Skim milk

e) Yogurt

2. A 25-year-old female meets with her family physician. She is interested in starting a family soon and is looking for advice on what nutritional supplements would be beneficial during pregnancy. Which of the two supplements should be considered as the most important?

a) Vitamin K and copper

b) Selenium and thiamine

c) Iron and folate

d) Vitamin C and D

e) Vitamin A and E

3. A 16 -year-old girl presents with severe menstrual camping, caused by increased prostaglandin production. Prostaglandins are synthesized from which of the following?

a) Arachidonic acid

b) Glucose

c) Acetyl co A

d) Palmitic acid

e) Propionyl co A

4. A 45 -year-old man presents with multiple gunshot wounds to the abdomen. He undergoes emergent surgery during which a part of his intestine is resected. After surgery, he is placed on total parenteral nutrition (TPN), an intravenous form of nutrition.TPN supplies essential fatty acids also in the diet. Which of the following is an essential fatty acid?

a) Palmitic acid

b) Linoleic acid

c) Elaidic acid

d) Oleic acid

e) Erucic acid

5. A 35-year-old woman presents with severe upper abdominal pain, nausea, and vomiting. She is diagnosed with pancreatitis (inflammation of the pancreas). Her serum triglyceride level is 1500 mg/dl (normal 150-199 mg/dl). Triglycerides are primarily synthesized in which of the following tissues?

a) Skeletal muscle

b) Heart muscle

c) Liver

d) Spleen

e) Red blood cells

6. An 8 -year-old boy has been brought to the emergency room with generalized tonic/clonic seizure. The child has a history of epilepsy and ataxia. Blood biochemistry reveals lactic acidosis. Upon questioning the parents state that their child was born with the disease, “Pyruvate carboxylase deficiency”. Which of the following products is the fate of pyruvate when the reaction is catalyzed by pyruvate carboxylase?

a) Lactate

b) Alanine

c) Acetyl co A

d) Oxaloacetate

e) Acetaldehyde

7. The catabolism of 1 mol of glucose to lactate in the glycolytic pathway is accompanied by the reduction of how many moles of O2?

a) 0

b) 2

c) 4

d) 8

e) 10

8. After digestion of a piece of cake that contains flour, milk, and sucrose as its primary ingredients, the major carbohydrate products entering the blood are-

a) Glucose

b) Galactose and fructose

c) Glucose and galactose

d) Glucose and fructose

e) Fructose, glucose, and galactose

9. Which of the following enzymes is not present in muscle?

a) Glycogen synthase

b) Lactate dehydrogenase

c) Glucose-6-Phosphatase

d) Hexokinase        

e) Phosphorylase

10. A 43-year-old man with a long history of poorly controlled hypertension presents to the emergency with a severe headache. His blood pressure is found to be dramatically elevated at 220/150 mm Hg. Which of the following products derived from amino acids, might bring down his highly elevated blood pressure?

a) Melanin

b) Nitric oxide

c) GABA

d) Dopamine

e) Serotonin

Answers

 1 – e) – Lactose intolerance is the inability or insufficient ability to digest lactose, a sugar found in milk and milk products. Lactase breaks down lactose into two simpler forms of sugar called glucose and galactose, which are then absorbed into the bloodstream. Lactose intolerance is caused by a deficiency of the enzyme lactase, which is produced by the cells lining the small intestine. Enzyme levels are highest shortly after birth and decline with aging, despite a continued intake of lactose.

Although the body’s ability to produce lactase cannot be changed, the symptoms of lactose intolerance can be managed with dietary changes. Most people with lactose intolerance can tolerate some amount of lactose in their diet. Gradually introducing small amounts of milk or milk products may help some people adapt to them with fewer symptoms. Lactose-free, lactose-reduced milk, Soy milk, and other products may be recommended.

The microorganisms that convert milk to yogurt (Streptococcus salivarius thermophilus and Lactobacillus delbrueckii bulgaricus) metabolize most of the lactose in the milk. Yogurt is also a good source of dietary calcium. Thus yogurt would cause the least difficulties and can be safely recommended to the patient.

2- c)- Pregnancy is a time of increased metabolic demand, and two of the most important supplements are Iron and folic acid; Iron to prevent anemia and folic acid to prevent neural tube defects in the developing fetus. Copper and selenium are the trace elements that are rarely deficient. Thiamine is present in grain products. Vitamin C and D are sufficiently obtained from the diet. Vitamin A derivatives are teratogenic and therefore should be avoided during pregnancy. Vitamin K deficiency is common in newborns and often the supplementation is required after birth.

3- a)- Prostaglandins are synthesized from Arachidonic acid; they cannot be synthesized from glucose, acetyl co A, Palmitic acid or propionyl co A.

Arachidonate, which may be obtained from the diet, but is usually derived from the 2nd position of phospholipids in the plasma membrane by the action of phospholipase A2, is the substrate for the synthesis of the prostanoids – prostaglandins (PG2) and thromboxane (TX2) series by the cyclooxygenase pathway, or the leukotrienes- LT4 and Lipoxins -LX4 series by the lipoxygenase pathway, with the two pathways competing for the arachidonate substrate.

4- b)- Linoleic acid is the right answer.  It has 18 carbon atoms and two double bonds (ω6), octadecadienoic acid. Linoleic (ω6), α-Linolenic (ω3) and Arachidonic acid (ω6) are the essential fatty acids. Arachidonic acid is relatively non-essential since it can be synthesized from Linoleic acid in the body.

Palmitic acid is a saturated fatty acid with 18 carbon atoms. Elaidic acid, Oleic acid, and Erucic acid are monounsaturated fatty acids (ω9). Elaidic and oleic are Trans and cis isomers respectively with 18 carbon atoms. Elaidic acid is the major Trans fat found in hydrogenated vegetable oils. Erucic acid has 22 carbon atoms and one double bond.

5- c) The liver is the right answer. Triglycerides are mainly synthesized in the liver but they can also be synthesized in the adipose tissue and intestinal cells. In the liver, they are packaged in VLDL and are secreted into the blood. The triglycerides synthesized in the intestine are packaged in chylomicrons and are transported to peripheral cells for utilization. Triglycerides cannot be synthesized in skeletal, heart muscle, spleen, and red blood cells. They are stored in adipose tissue and liver.

6- d) The right answer is (d) – Oxaloacetate. Pyruvate carboxylase catalyzes the conversion of pyruvate to oxaloacetate. It is the first step of gluconeogenesis and is also considered an “anaplerotic” or “filling up” or “CO2 fixation reaction” to replenish the oxaloacetate concentration in conditions of a sudden influx of Acetyl co A, for the optimum functioning of TCA cycle. Biotin is required as a cofactor in this energy-requiring reaction.

Lactate is the product of lactate dehydrogenase catalyzed reaction. Alanine is produced by a transamination reaction catalyzed by Alanine transferase (ALT) also called SGPT (Serum glutamate pyruvate transaminase).

Acetyl co A is the product of pyruvate dehydrogenase reaction. Acetaldehyde is the product of pyruvate decarboxylase catalyzed reaction that does not occur in human beings. This reaction is common in microorganisms and is commercially used for the fermentation of glucose for wine production.

7- a) Production of lactate through glycolysis takes place under anaerobic conditions. No oxygen is used; hence the right answer is zero (0). Glycolysis can provide energy in the absence of oxygen; it is the unique pathway that can operate both aerobically as well as anaerobically. One mol of glucose yields 2 moles of lactate, with a yield of 2ATP by substrate-level phosphorylation. In aerobic respiration, via Electron transport chain O2 is used as a final acceptor and is reduced to water.

8) -e) – As per the ingredients, the products would be- Glucose, galactose, and fructose.

Flour- Starch-Starch is a polymer of glucose. The digestion of starch would produce glucose.

Milk- Lactose (milk sugar). Lactose is a disaccharide of galactose and glucose. Thus the digestion products of milk would be galactose and glucose. Sucrose is a disaccharide, made up of glucose and fructose. Digestion by sucrase in the intestine would produce glucose and fructose. In the end, the net products of digestion entering blood would be – Glucose, galactose, and fructose.

9- c) – Glucose-6-phosphatase is not present in muscle and does not contribute to blood glucose. Glucose-6-p produced from gluconeogenesis or from the degradation of glycogen is channeled towards glycolytic pathway in muscle. Lactate dehydrogenase is not absent in muscle. In fact, excessive lactate accumulation is the reason for muscle fatigue and the lactate produced from pyruvate by the action of lactate dehydrogenase is transported through the blood to the liver for glucose production (Cori’s cycle). Hexokinase is the first enzyme of the glycolytic pathway, glycogen synthase is the rate-controlling enzyme of glycogenesis synthesis and phosphorylase is the rate-limiting enzyme of glycogen degradation, all these three are present in the muscle.

10- b) Hypertensive emergencies require an immediate lowering of blood pressure. This may be accomplished with IV nitroprusside, a short-acting vasodilator with a rapid onset of action that allows for minute-to-minute control of blood pressure. Nitroprusside acts by releasing Nitric oxide (NO). Nitric oxide was previously referred to as an endothelial-derived relaxing factor. It is a smooth muscle relaxant and a potent vasodilator. Nitroglycerin, amyl nitrite, (isobutyl nitrite or similar) and other nitrite derivatives used in the treatment of heart disease are also converted to nitric oxide, which in turn dilates the coronary arteries, thereby increasing the blood supply.

Melanin is derived from Tyrosine and is the major pigment of skin and hair.

GABA (gamma-aminobutyric acid), a decarboxylation product of glutamic acid is an inhibitory neurotransmitter.

Dopamine is derived from the decarboxylation of DOPA, which is a product of tyrosine. Dopamine is used for raising the blood pressure in patients of shock. It is a stimulatory neurotransmitter.

Serotonin is derived from tryptophan; it is also a vasoconstrictor and a stimulatory neurotransmitter. Serotonin is involved in mood elevation and depression.