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Kuwait MOH Dietitian practice questions

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Question 1Nutrition Science and Macronutrient Metabolism

Which monosaccharide is the primary fuel used by the brain and red blood cells under normal physiological conditions?

  1. Galactose
  2. Glucose Correct answer.
  3. Ribose
  4. Fructose

Explanation

Glucose is the obligate fuel for red blood cells and the preferred substrate for brain tissue because these cells lack the capacity for meaningful ketone or fructose utilization under fed conditions. Fructose and galactose must first be converted in the liver before entering glycolytic pathways.

Question 2Nutrition Science and Macronutrient Metabolism

A dietitian calculates that a 70 kg adult receiving 1.2 g/kg/day of protein consumes approximately how many grams of protein daily?

  1. 120 g
  2. 96 g
  3. 84 g Correct answer.
  4. 70 g

Explanation

Multiplying body weight by the prescribed factor gives 70 × 1.2 = 84 g of protein per day. This calculation is routine when translating g/kg recommendations into practical food prescriptions.

Question 3Nutrition Science and Macronutrient Metabolism

Which lipid fraction carries the greatest share of circulating triacylglycerol in the postprandial state?

  1. Chylomicrons Correct answer.
  2. Low-density lipoprotein
  3. High-density lipoprotein
  4. Free fatty acids bound to albumin

Explanation

Chylomicrons are assembled in enterocytes and transport dietary triacylglycerol through lymph into plasma after a meal, so they dominate postprandial triglyceride carriage. LDL and HDL are mostly cholesterol carriers, and albumin-bound fatty acids reflect adipose lipolysis rather than absorbed dietary fat.

Question 4Nutrition Science and Macronutrient Metabolism

Which enzyme initiates starch digestion in the oral cavity?

  1. Lactase
  2. Pepsin
  3. Pancreatic lipase
  4. Salivary amylase Correct answer.

Explanation

Salivary alpha-amylase hydrolyses internal alpha-1,4 glycosidic bonds of starch, producing dextrins and maltose before the bolus reaches the stomach. Pepsin acts on protein, lipase on fat, and lactase on the disaccharide lactose.

Question 5Nutrition Science and Macronutrient Metabolism

Which amino acid is classified as conditionally essential because synthesis may become insufficient during critical illness?

  1. Alanine
  2. Asparagine
  3. Serine
  4. Glutamine Correct answer.

Explanation

Glutamine is the most abundant free amino acid and becomes conditionally essential when demand by enterocytes and immune cells outpaces endogenous synthesis during catabolic stress. Alanine, asparagine and serine are readily synthesized in adequate amounts.

Question 6Nutrition Science and Macronutrient Metabolism

Which dietary component provides the most energy per gram?

  1. Fat Correct answer.
  2. Protein
  3. Alcohol
  4. Available carbohydrate

Explanation

Fat supplies approximately 9 kcal per gram, compared with about 4 kcal/g for protein and carbohydrate and 7 kcal/g for alcohol. This energy density explains why fat reduction is a common strategy in weight-management counselling.

Question 7Nutrition Science and Macronutrient Metabolism

Which form of stored carbohydrate is found in human liver and muscle?

  1. Glycogen Correct answer.
  2. Cellulose
  3. Inulin
  4. Amylose

Explanation

Glycogen is the branched glucose polymer stored in hepatocytes and myocytes for maintaining blood glucose and fueling contraction respectively. Amylose, cellulose and inulin are plant polysaccharides that human enzymes cannot fully digest.

Question 8Nutrition Science and Macronutrient Metabolism

Which vitamin is a coenzyme required for the oxidative decarboxylation of pyruvate to acetyl-CoA?

  1. Thiamine Correct answer.
  2. Cobalamin
  3. Ascorbic acid
  4. Tocopherol

Explanation

Thiamine pyrophosphate is the coenzyme of the pyruvate dehydrogenase complex, linking glycolysis to the citric acid cycle. Deficiency therefore impairs glucose oxidation and can precipitate wet beriberi or Wernicke encephalopathy.

Question 9Nutrition Science and Macronutrient Metabolism

A patient with newly diagnosed type 2 diabetes asks how carbohydrate intake affects glycaemia. Which statement best reflects current nutrition practice?

  1. Carbohydrate must be eliminated entirely to control glucose
  2. Only simple sugars raise glucose, while starches do not
  3. Total carbohydrate and food source both influence postprandial glucose Correct answer.
  4. Carbohydrate quantity is irrelevant if protein intake is high

Explanation

Both the amount and the type of carbohydrate, including fibre content and glycaemic index, affect postprandial glucose excursions, so counselling emphasises consistent distribution and quality rather than total elimination. Very low carbohydrate diets are an option but not a universal requirement.

Question 10Nutrition Science and Macronutrient Metabolism

A vegan client consumes adequate total protein but relies solely on wheat and rice. Which strategy best improves protein quality?

  1. Consuming all protein in a single meal
  2. Reducing fibre to enhance absorption
  3. Combining cereals with legumes to complement amino acid patterns Correct answer.
  4. Increasing total fat intake

Explanation

Cereals are limiting in lysine while legumes are limiting in methionine, so combining them within the day supplies a more complete essential amino acid profile. Modern evidence indicates complementation need not occur at every meal.

Question 11Nutrition Science and Macronutrient Metabolism

Which biochemical marker is most appropriate for assessing long-term glycaemic control in a patient with type 2 diabetes?

  1. Urinary ketones
  2. Fasting plasma glucose
  3. Random capillary glucose
  4. Glycated haemoglobin Correct answer.

Explanation

Glycated haemoglobin reflects average glucose exposure over the preceding two to three months, making it the standard index of chronic control. Fasting and random glucose capture only a single time point.

Question 12Nutrition Science and Macronutrient Metabolism

A patient with chronic kidney disease not on dialysis has an eGFR of 35 mL/min/1.73 m². Which protein prescription is generally recommended?

  1. 1.2–1.5 g/kg/day
  2. 2.5 g/kg/day
  3. 1.8–2.0 g/kg/day
  4. 0.6–0.8 g/kg/day Correct answer.

Explanation

Guidelines advise roughly 0.6–0.8 g/kg/day of protein for non-dialysed chronic kidney disease to limit hyperfiltration and nitrogenous waste while preserving nutritional status. Higher intakes are reserved for dialysis or catabolic states.

Question 13Nutrition Science and Macronutrient Metabolism

Which fatty acid is the parent of the omega-3 series and must be supplied by diet?

  1. Oleic acid
  2. Alpha-linolenic acid Correct answer.
  3. Linoleic acid
  4. Palmitic acid

Explanation

Alpha-linolenic acid (18:3 n-3) cannot be synthesized by humans because they lack the desaturase needed beyond the delta-9 position, so it is an essential fatty acid. Linoleic acid is the parent of the omega-6 series.

Question 14Nutrition Science and Macronutrient Metabolism

Which metabolic state is characterised by increased hepatic ketogenesis?

  1. Moderate aerobic exercise after breakfast
  2. Immediately after a carbohydrate-rich meal
  3. Ingestion of a high-protein snack
  4. Prolonged fasting Correct answer.

Explanation

Prolonged fasting lowers insulin and raises glucagon, promoting lipolysis and hepatic conversion of fatty acids to ketone bodies for use by brain and muscle. Postprandial insulin suppresses ketogenesis.

Question 15Nutrition Science and Macronutrient Metabolism

A client reports bloating after increasing fibre intake. Which recommendation is most appropriate?

  1. Remove all fibre sources permanently
  2. Add fibre only at the evening meal
  3. Increase fibre gradually with adequate fluid intake Correct answer.
  4. Substitute fruit juice for whole fruit

Explanation

Gradual titration of fibre with sufficient fluid allows the gut microbiota and motility to adapt and reduces gas and bloating. Abrupt large increases are the usual cause of intolerance.

Question 16Nutrition Science and Macronutrient Metabolism

Which statement about the thermic effect of food is accurate?

  1. It is highest for protein and lowest for fat Correct answer.
  2. It accounts for about half of daily energy expenditure
  3. It is identical for all macronutrients
  4. It is highest for fat and lowest for protein

Explanation

Protein has the highest thermic effect, roughly 20–30% of its energy, because of costs of deamination and peptide synthesis, whereas fat costs only about 0–3%. The thermic effect of food overall contributes around 10% of total energy expenditure.

Question 17Nutrition Science and Macronutrient Metabolism

Which hormone promotes glycogenolysis and gluconeogenesis during fasting?

  1. Glucagon Correct answer.
  2. Insulin
  3. Adiponectin
  4. Leptin

Explanation

Glucagon, secreted by pancreatic alpha cells in response to falling glucose, stimulates hepatic glycogen breakdown and gluconeogenesis to maintain blood glucose. Insulin has the opposite anabolic action.

Question 18Nutrition Science and Macronutrient Metabolism

A patient with lactose intolerance wants to maintain calcium intake. Which approach is most suitable?

  1. Use lactose-free milk or small portions of yoghurt with meals Correct answer.
  2. Consume milk only on an empty stomach
  3. Avoid all dairy products permanently
  4. Replace dairy with calcium supplements alone

Explanation

Lactose-free milk and fermented products such as yoghurt provide calcium with reduced or partially digested lactose, and consuming them with meals slows gastric emptying and improves tolerance. Complete dairy avoidance risks inadequate calcium and protein.

Question 19Nutrition Science and Macronutrient Metabolism

Which factor most increases dietary iron bioavailability from a plant-based meal?

  1. Adding calcium-rich foods
  2. Adding phytate-rich bran
  3. Adding a source of vitamin C Correct answer.
  4. Adding tea with the meal

Explanation

Ascorbic acid reduces ferric iron to the more absorbable ferrous form and chelates it, counteracting inhibitors. Tannins in tea, calcium and phytates all reduce non-haem iron absorption.

Question 20Nutrition Science and Macronutrient Metabolism

A client following a very low carbohydrate ketogenic diet reports fatigue and dizziness in the first week. Which explanation is most plausible?

  1. Increased insulin secretion
  2. Sodium and water loss accompanying glycogen depletion Correct answer.
  3. Excess protein intake
  4. Excessive dietary fibre

Explanation

Restricting carbohydrate depletes glycogen, and each gram of glycogen stores water, so natriuresis and diuresis follow, producing transient hypovolaemia and electrolyte loss often called keto flu. Adequate sodium and fluid usually relieve symptoms.

Question 21Nutrition Science and Macronutrient Metabolism

Which amino acid serves as the primary precursor for hepatic gluconeogenesis during prolonged fasting?

  1. Lysine
  2. Phenylalanine
  3. Alanine Correct answer.
  4. Leucine

Explanation

Alanine released from muscle undergoes the glucose-alanine cycle, transferring nitrogen to the liver while its carbon skeleton feeds gluconeogenesis. Leucine and lysine are strictly ketogenic, and phenylalanine is not a major gluconeogenic precursor.

Question 22Nutrition Science and Macronutrient Metabolism

A patient with cirrhosis and ascites requires nutrition support. Which approach best balances protein needs and fluid restriction?

  1. Restrict all sodium and protein simultaneously without monitoring
  2. Give only intravenous glucose until ascites resolves
  3. Restrict protein to 0.4 g/kg/day to reduce ammonia
  4. Provide 1.2–1.5 g/kg/day protein with concentrated energy-dense formulas Correct answer.

Explanation

Cirrhotic patients are catabolic and need 1.2–1.5 g/kg/day of protein, and energy-dense, low-volume formulas help meet needs while managing fluid restriction. Protein restriction is no longer recommended because it worsens sarcopenia without reliably improving encephalopathy.

Question 23Nutrition Science and Macronutrient Metabolism

Which statement best explains why medium-chain triglycerides are preferred in some fat malabsorption states?

  1. They require micelle formation for absorption
  2. They are stored preferentially in adipose tissue
  3. They inhibit pancreatic lipase activity
  4. They are absorbed directly into portal blood without chylomicron formation Correct answer.

Explanation

Medium-chain triglycerides are water-soluble enough to be absorbed and transported via the portal vein bound to albumin, bypassing bile salt micelles and chylomicron assembly. This makes them useful in cholestasis and lymphatic obstruction.

Question 24Nutrition Science and Macronutrient Metabolism

A researcher observes that a high-protein meal raises postprandial amino acid availability but does not raise blood glucose. Which mechanism best explains this?

  1. Amino acids are converted entirely to ketone bodies
  2. Insulin and glucagon responses support amino acid uptake and modest gluconeogenesis without net hyperglycaemia Correct answer.
  3. Protein is not digested in the small intestine
  4. Dietary protein inhibits all glucose production

Explanation

Protein ingestion raises insulin and glucagon together, promoting amino acid uptake into tissues while hepatic gluconeogenesis is modest and offset by reduced glycogenolysis, so net glucose remains stable. Complete conversion to ketones or absent digestion would not match the observed aminoacidaemia.

Question 25Nutrition Science and Macronutrient Metabolism

In a patient with short bowel syndrome and massive ileal resection, which nutritional consequence is most expected?

  1. Impaired absorption of bile salts and fat-soluble vitamins Correct answer.
  2. Increased absorption of vitamin B12
  3. Increased gastric acid neutralisation
  4. Enhanced enterohepatic circulation of bile acids

Explanation

The terminal ileum is the site of bile salt and vitamin B12 absorption, so resection causes bile salt malabsorption, steatorrhoea and deficiency of fat-soluble vitamins. Loss of bile salts also reduces micellar fat digestion.

Question 26Nutrition Science and Macronutrient Metabolism

Which statement correctly describes the energy yield of the three macronutrients when metabolised in the body?

  1. Carbohydrate provides 9 kcal/g, protein provides 4 kcal/g, and fat provides 4 kcal/g.
  2. Carbohydrate provides 4 kcal/g, protein provides 9 kcal/g, and fat provides 4 kcal/g.
  3. Carbohydrate provides 7 kcal/g, protein provides 4 kcal/g, and fat provides 9 kcal/g.
  4. Carbohydrate provides 4 kcal/g, protein provides 4 kcal/g, and fat provides 9 kcal/g. Correct answer.

Explanation

The Atwater general factors assign 4 kcal per gram to carbohydrate and protein and 9 kcal per gram to fat. These values are used in dietetic practice to estimate the energy content of foods and diets. Alcohol is separately assigned 7 kcal/g, which is not one of the three macronutrients.

Question 27Nutrition Science and Macronutrient Metabolism

Which statement best describes the role of dietary fibre in glycaemic control?

  1. Insoluble fibre forms a gel in the stomach that delays carbohydrate digestion and lowers blood glucose.
  2. Fibre has no effect on postprandial glycaemia because it is not absorbed in the small intestine.
  3. Soluble fibre slows gastric emptying and glucose absorption, reducing postprandial glycaemic excursions. Correct answer.
  4. Dietary fibre increases the glycaemic index of carbohydrate foods by accelerating glucose release.

Explanation

Soluble fibres such as beta-glucan and pectin form viscous gels that slow gastric emptying and the absorption of glucose, blunting postprandial glucose peaks. Insoluble fibres mainly add bulk and promote laxation rather than forming gels. Fibre is not absorbed, but its physicochemical effects in the gut do influence glycaemia.

Question 28Nutrition Science and Macronutrient Metabolism

A 30-year-old man with phenylketonuria (PKU) is planning a pregnancy with his partner. He asks whether his diet affects the risk to the child. Which statement is the most appropriate response?

  1. Phenylalanine restriction is only necessary for the mother with PKU, not for the father.
  2. He should maintain strict phenylalanine restriction before conception to prevent fetal hyperphenylalaninaemia. Correct answer.
  3. His phenylalanine intake does not affect the fetus because PKU is inherited and the mother's diet determines fetal exposure.
  4. His partner should follow a low-phenylalanine diet during pregnancy to protect the fetus.

Explanation

In PKU, elevated maternal phenylalanine is teratogenic to the fetus, but the father's phenylalanine levels do not directly expose the fetus. However, men with PKU are advised to maintain metabolic control before conception because elevated phenylalanine can affect spermatogenesis and overall health, and because a father with PKU may transmit the gene. The key point is that the father's diet does not directly determine fetal phenylalanine exposure; the mother's phenylalanine level does.

Question 29Nutrition Science and Macronutrient Metabolism

A patient with type 2 diabetes and stage 3 chronic kidney disease (eGFR 45 mL/min/1.73 m²) asks about protein intake. Which prescription is most appropriate?

  1. 1.2 g/kg/day of protein to prevent malnutrition.
  2. 0.8 g/kg/day of mixed protein, avoiding excessive animal protein. Correct answer.
  3. 1.5 g/kg/day of protein to compensate for renal losses.
  4. 0.6 g/kg/day of high-biological-value protein to reduce hyperfiltration.

Explanation

For patients with diabetes and stage 3 CKD not on dialysis, guidelines recommend a protein intake of approximately 0.8 g/kg/day, similar to the general population, because lower intakes have not consistently slowed progression and may increase malnutrition risk. Higher intakes may worsen hyperfiltration and are not routinely advised. Very low intakes require careful monitoring and are not first-line.

Question 30Nutrition Science and Macronutrient Metabolism

A client with short bowel syndrome after extensive ileal resection is at risk for which specific nutritional deficiency?

  1. Calcium deficiency due to loss of the jejunum.
  2. Thiamine deficiency due to reduced gastric acid production.
  3. Vitamin B12 deficiency due to loss of the terminal ileum, the site of intrinsic factor–B12 receptor activity. Correct answer.
  4. Iron deficiency due to impaired absorption in the duodenum.

Explanation

The terminal ileum is the exclusive site for absorption of the vitamin B12–intrinsic factor complex, so its resection leads to B12 deficiency requiring lifelong parenteral supplementation. Iron is absorbed mainly in the duodenum, calcium in the duodenum and jejunum, and thiamine in the jejunum and ileum, so these are less specifically affected by ileal resection.

Question 31Micronutrients, Biochemistry, and Physiology

Which vitamin functions as the precursor for the coenzyme NAD+, which is essential for hydrogen transfer in cellular respiration?

  1. Pyridoxine
  2. Niacin Correct answer.
  3. Thiamine
  4. Riboflavin

Explanation

Niacin (vitamin B3) is incorporated into the coenzymes NAD and NADP, which carry electrons and hydrogen in oxidation-reduction reactions of glycolysis, the Krebs cycle, and the electron transport chain. Riboflavin forms FMN and FAD, thiamine forms TPP, and pyridoxine forms pyridoxal phosphate, so each of those serves different coenzyme roles.

Question 32Micronutrients, Biochemistry, and Physiology

A patient presents with night blindness and Bitot spots on conjunctival examination. Deficiency of which micronutrient best explains these findings?

  1. Vitamin D
  2. Vitamin E
  3. Vitamin K
  4. Vitamin A Correct answer.

Explanation

Vitamin A is required for rhodopsin synthesis in the retina and for maintaining epithelial integrity, so deficiency causes night blindness and xerophthalmia with Bitot spots. The other fat-soluble vitamins serve different roles: calcium homeostasis, antioxidant protection, and coagulation factor carboxylation.

Question 33Micronutrients, Biochemistry, and Physiology

Which mineral is an essential component of the thyroid hormones thyroxine (T4) and triiodothyronine (T3)?

  1. Selenium
  2. Iodine Correct answer.
  3. Zinc
  4. Iron

Explanation

Iodine is covalently incorporated into the tyrosine residues of thyroglobulin to form T3 and T4, making it indispensable for thyroid hormone synthesis. Iron, zinc, and selenium support other functions such as hemoglobin synthesis, enzyme catalysis, and deiodinase activity, but they are not structural components of the hormones themselves.

Question 34Micronutrients, Biochemistry, and Physiology

Which enzyme catalyzes the rate-limiting step of glycolysis, the phosphorylation of glucose to glucose-6-phosphate?

  1. Hexokinase Correct answer.
  2. Phosphofructokinase-1
  3. Glucose-6-phosphatase
  4. Pyruvate kinase

Explanation

Hexokinase (glucokinase in the liver) catalyzes the ATP-dependent phosphorylation of glucose to glucose-6-phosphate, trapping glucose inside the cell. Phosphofructokinase-1 is the major regulatory step but acts later on fructose-6-phosphate, pyruvate kinase acts at the end of glycolysis, and glucose-6-phosphatase reverses the hexokinase reaction in the liver.

Question 35Micronutrients, Biochemistry, and Physiology

Which vitamin acts as the primary antioxidant in cell membranes, protecting polyunsaturated fatty acids from lipid peroxidation?

  1. Vitamin B12
  2. Vitamin E Correct answer.
  3. Vitamin C
  4. Folate

Explanation

Vitamin E (alpha-tocopherol) is lipid-soluble and resides in membrane phospholipid bilayers, where it scavenges peroxyl radicals and halts lipid peroxidation. Vitamin C is a water-soluble antioxidant that can regenerate tocopherol, while B12 and folate are involved in one-carbon metabolism and blood formation.

Question 36Micronutrients, Biochemistry, and Physiology

Which trace element is central to the structure of hemoglobin and is absorbed in the duodenum in the ferrous (Fe2+) form?

  1. Chromium
  2. Copper
  3. Iron Correct answer.
  4. Manganese

Explanation

Iron is incorporated into the heme ring of hemoglobin, where the ferrous ion binds oxygen reversibly. Absorption occurs in the duodenum, with Fe2+ taken up by DMT1 more efficiently than Fe3+, which must first be reduced. Copper assists iron export but is not part of the heme structure.

Question 37Micronutrients, Biochemistry, and Physiology

A patient on long-term warfarin therapy is counseled about dietary consistency. Which vitamin intake should be kept stable to avoid fluctuations in anticoagulant effect?

  1. Vitamin D
  2. Vitamin A
  3. Vitamin K Correct answer.
  4. Vitamin B6

Explanation

Warfarin inhibits vitamin K epoxide reductase, reducing the regeneration of reduced vitamin K needed for gamma-carboxylation of clotting factors II, VII, IX, and X. A sudden increase in vitamin K intake from leafy greens can overcome the blockade and lower the INR, so intake should be consistent rather than eliminated.

Question 38Micronutrients, Biochemistry, and Physiology

A child with poor sunlight exposure has low serum calcium, low phosphate, and elevated alkaline phosphatase. Which deficiency best explains this biochemical pattern?

  1. Iron deficiency
  2. Thiamine deficiency
  3. Vitamin C deficiency
  4. Vitamin D deficiency Correct answer.

Explanation

Vitamin D deficiency limits intestinal calcium and phosphate absorption, causing hypocalcemia and hypophosphatemia, while elevated alkaline phosphatase reflects increased bone turnover in rickets. The other deficiencies do not produce this combination of low calcium, low phosphate, and high alkaline phosphatase.

Question 39Micronutrients, Biochemistry, and Physiology

Which coenzyme form of thiamine is required for the oxidative decarboxylation of pyruvate to acetyl-CoA?

  1. Biotin
  2. Thiamine pyrophosphate Correct answer.
  3. Pyridoxal phosphate
  4. Tetrahydrofolate

Explanation

Thiamine pyrophosphate (TPP) is the coenzyme for the pyruvate dehydrogenase complex, which decarboxylates pyruvate and transfers the acetyl group to coenzyme A. Pyridoxal phosphate serves amino acid reactions, biotin serves carboxylation reactions, and tetrahydrofolate carries one-carbon units.

Question 40Micronutrients, Biochemistry, and Physiology

In the electron transport chain, which mineral is a component of cytochrome c oxidase (complex IV) and is essential for the final transfer of electrons to oxygen?

  1. Zinc
  2. Selenium
  3. Copper Correct answer.
  4. Magnesium

Explanation

Complex IV (cytochrome c oxidase) contains copper centers (CuA and CuB) and heme iron that together reduce molecular oxygen to water. Copper deficiency can impair oxidative phosphorylation, while zinc, selenium, and magnesium serve unrelated roles in this context.

Question 41Micronutrients, Biochemistry, and Physiology

Which micronutrient deficiency is the most common cause of preventable childhood blindness worldwide, largely through corneal damage in severe xerophthalmia?

  1. Riboflavin
  2. Vitamin A Correct answer.
  3. Zinc
  4. Vitamin B12

Explanation

Severe vitamin A deficiency progresses from night blindness to conjunctival xerosis, Bitot spots, and corneal ulceration that can lead to blindness, making it the leading preventable cause of childhood blindness globally. Riboflavin, zinc, and B12 deficiencies do not cause this corneal sequence.

Question 42Micronutrients, Biochemistry, and Physiology

A vegan patient has macrocytic anemia with hypersegmented neutrophils and elevated methylmalonic acid. Which deficiency best fits these findings?

  1. Folate deficiency
  2. Vitamin B12 deficiency Correct answer.
  3. Vitamin C deficiency
  4. Iron deficiency

Explanation

Vitamin B12 deficiency produces megaloblastic anemia with hypersegmented neutrophils because impaired methionine synthase blocks DNA synthesis, and elevated methylmalonic acid distinguishes B12 from folate deficiency. Folate deficiency causes megaloblastic anemia but methylmalonic acid remains normal, since methylmalonyl-CoA mutase requires adenosylcobalamin.

Question 43Micronutrients, Biochemistry, and Physiology

Which enzyme requires zinc as a cofactor and catalyzes the interconversion of carbon dioxide and bicarbonate?

  1. Lactate dehydrogenase
  2. Carbonic anhydrase Correct answer.
  3. Alkaline phosphatase
  4. Glutathione peroxidase

Explanation

Carbonic anhydrase contains a zinc ion at its active site that polarizes water and enables rapid hydration of carbon dioxide to bicarbonate, a reaction central to acid-base balance and CO2 transport. Lactate dehydrogenase uses NADH, alkaline phosphatase is a metalloenzyme with zinc and magnesium but catalyzes phosphate hydrolysis, and glutathione peroxidase requires selenium.

Question 44Micronutrients, Biochemistry, and Physiology

In a patient with chronic kidney disease, which form of vitamin D should be used to bypass impaired renal 1-alpha-hydroxylation?

  1. Calcitriol Correct answer.
  2. Cholecalciferol
  3. 7-Dehydrocholesterol
  4. Ergocalciferol

Explanation

Calcitriol is the active 1,25-dihydroxyvitamin D form and does not require renal 1-alpha-hydroxylation, so it is effective when kidney function is reduced. Cholecalciferol and ergocalciferol are precursors that still need hepatic and renal activation, and 7-dehydrocholesterol is a skin precursor.

Question 45Micronutrients, Biochemistry, and Physiology

Which water-soluble vitamin is a coenzyme for carboxylase enzymes, including pyruvate carboxylase and acetyl-CoA carboxylase, and is bound by avidin in raw egg white?

  1. Pantothenic acid
  2. Thiamine
  3. Biotin Correct answer.
  4. Niacin

Explanation

Biotin is covalently attached to carboxylase enzymes and carries activated CO2 during carboxylation reactions such as gluconeogenesis and fatty acid synthesis. Avidin in raw egg white binds biotin tightly and prevents its absorption, which can cause deficiency with prolonged raw egg consumption.

Question 46Micronutrients, Biochemistry, and Physiology

Which mineral is required for the antioxidant enzyme glutathione peroxidase, whose activity helps protect red blood cells from oxidative hemolysis?

  1. Copper
  2. Manganese
  3. Selenium Correct answer.
  4. Chromium

Explanation

Selenium is incorporated as selenocysteine into glutathione peroxidase, which reduces hydrogen peroxide and lipid hydroperoxides using glutathione. This protects erythrocyte membranes from oxidative damage, and selenium deficiency can contribute to hemolytic anemia in susceptible individuals.

Question 47Micronutrients, Biochemistry, and Physiology

A patient with chronic alcoholism develops Wernicke encephalopathy with ataxia, confusion, and ophthalmoplegia. Which biochemical consequence of thiamine deficiency underlies this presentation?

  1. Impaired oxidative decarboxylation of pyruvate and reduced alpha-ketoglutarate dehydrogenase activity Correct answer.
  2. Impaired conversion of phenylalanine to tyrosine
  3. Impaired deamination of glutamate to alpha-ketoglutarate
  4. Impaired carboxylation of pyruvate to oxaloacetate

Explanation

Thiamine pyrophosphate is required by pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase, so deficiency reduces ATP production in highly oxidative tissues such as the brain. The resulting energy failure and lactate accumulation in vulnerable regions produce the classic triad of Wernicke encephalopathy.

Question 48Micronutrients, Biochemistry, and Physiology

A patient with malabsorption has prolonged prothrombin time that corrects with vitamin K administration, while platelet count and fibrinogen are normal. Which vitamin K-dependent factor is most likely deficient in this scenario?

  1. Fibrinogen
  2. Factor VIII
  3. Factor VII Correct answer.
  4. Factor V

Explanation

Factor VII has the shortest half-life among the vitamin K-dependent factors (II, VII, IX, X), so its deficiency raises the prothrombin time earliest when vitamin K is lacking. Factor VIII and factor V are not vitamin K-dependent, and fibrinogen is measured separately and was normal here.

Question 49Micronutrients, Biochemistry, and Physiology

A patient with cystic fibrosis has fat-soluble vitamin deficiencies despite adequate intake. Which physiologic mechanism best explains this pattern?

  1. Impaired micelle formation due to reduced pancreatic lipase and bile salt availability Correct answer.
  2. Increased renal tubular reabsorption of tocopherol
  3. Enhanced hepatic synthesis of retinol-binding protein
  4. Upregulation of intestinal fatty acid translocase

Explanation

Fat-soluble vitamins A, D, E, and K require bile salts and pancreatic lipase to form micelles for efficient absorption. In cystic fibrosis, pancreatic insufficiency and altered bile flow impair micelle formation, so deficiencies develop even when dietary intake is adequate.

Question 50Micronutrients, Biochemistry, and Physiology

During prolonged fasting, which biochemical pathway becomes the major source of glucose, and which vitamin-derived coenzyme is required for its rate-limiting carboxylation step?

  1. Glycolysis; thiamine
  2. Pentose phosphate pathway; riboflavin
  3. Glycogenolysis; pyridoxal phosphate
  4. Gluconeogenesis; biotin Correct answer.

Explanation

During prolonged fasting, gluconeogenesis in the liver and kidney supplies glucose, and its first committed step is the biotin-dependent carboxylation of pyruvate to oxaloacetate by pyruvate carboxylase. Glycogenolysis only sustains glucose briefly, and the other coenzymes are not required for this carboxylation.