Nutrition and Metabolism Practice Questions

Q: Which of the following caseins predominates in cow milk?

alpha-casein. **Explanation:** **Casein** is the primary group of phosphoproteins found in mammalian milk, accounting for approximately 80% of the total protein content in cow milk. It exists in several molecular forms: alpha ($\alpha$), beta ($\beta$), and kappa ($\kappa$) caseins. 1. **Why Alpha-casein is Correct:** In bovine (cow) milk, **alpha-casein ($\alpha$-casein)** is the most abundant fraction, representing roughly 45–50% of the total casein content. It is further subdivided into $\alpha_{s1}$ and $\alpha_{s2}$ types. This high concentration of $\alpha$-casein is a distinguishing feature of cow milk compared to human milk. 2. **Why Other Options are Incorrect:** * **Beta-casein:** While present in cow milk (about 35%), it is not the predominant form. Interestingly, $\beta$-casein is the **predominant** casein in **human milk**. * **Equally present:** The distribution is not equal; the ratio in cow milk is roughly 3:2:1 for $\alpha$, $\beta$, and $\kappa$ caseins respectively. **High-Yield Facts for NEET-PG:** * **Casein vs. Whey:** Cow milk has a Casein:Whey ratio of **80:20**, whereas human milk has a ratio of **40:60**. This makes human milk easier to digest for infants. * **Curd Formation:** Casein precipitates at its isoelectric point (**pH 4.6**), which is the biochemical basis for curd formation. * **Micelles:** Caseins are held together in "micelles" by **Calcium Phosphate** bridges. * **Clinical Pearl:** The high $\alpha$-casein content and the higher casein-to-whey ratio in cow milk lead to the formation of a **hard, tough curd** in the infant's stomach, which is why unmodified cow milk is unsuitable for human neonates.

Q: Chromium deficiency may lead to which of the following?

Insulin dysfunction. **Explanation:** **1. Why Insulin Dysfunction is Correct:** Chromium (specifically the trivalent form, $Cr^{3+}$) is an essential trace element that plays a critical role in carbohydrate and lipid metabolism. It functions as a component of **Chromodulin** (also known as Glucose Tolerance Factor or GTF). Chromodulin enhances the action of insulin by increasing the sensitivity of insulin receptors on target cells. Therefore, chromium deficiency leads to impaired glucose tolerance, insulin resistance, and a clinical picture mimicking Type 2 Diabetes Mellitus. **2. Why Other Options are Incorrect:** * **Cardiomyopathy:** This is characteristically associated with **Selenium deficiency** (Keshan disease). While severe Thiamine (Vitamin B1) deficiency can cause "Wet Beriberi" (high-output heart failure), chromium is not linked to primary myocardial pathology. * **Endocarditis:** This is an inflammatory/infectious condition of the heart valves, typically caused by bacteria (e.g., *Staphylococcus aureus*) or fungi, and is unrelated to trace element deficiencies. * **External Ophthalmoplegia:** This is a hallmark of **Thiamine (B1) deficiency** (Wernicke-Korsakoff syndrome) or certain mitochondrial myopathies. It is not a feature of chromium deficiency. **3. High-Yield Clinical Pearls for NEET-PG:** * **Chromodulin Mechanism:** It facilitates the binding of insulin to its receptor and stimulates tyrosine kinase activity. * **Trivalent vs. Hexavalent:** $Cr^{3+}$ is the nutritional form; $Cr^{6+}$ (Hexavalent) is industrial and highly toxic/carcinogenic. * **TPN Association:** Chromium deficiency is most commonly seen in patients on long-term **Total Parenteral Nutrition (TPN)** without adequate trace element supplementation. * **Key Deficiency Sign:** Unexplained hyperglycemia and weight loss in a patient on TPN.

Q: A child presents with growth retardation, hypogonadism, alopecia, and immunodeficiency. The child has a deficiency of which of the following nutrients?

Zinc. **Explanation:** The clinical presentation of **growth retardation, hypogonadism, alopecia, and immunodeficiency** is a classic manifestation of **Zinc deficiency**. Zinc is an essential trace element required for the function of over 300 enzymes (e.g., Carbonic anhydrase, Alkaline phosphatase, Alcohol dehydrogenase). It plays a pivotal role in DNA synthesis, cell division, and protein synthesis, which explains why its deficiency primarily affects rapidly dividing cells (skin, immune system, and gonads). * **Why Zinc is correct:** Zinc is crucial for the "Zinc-finger motif" in transcription factors and for the activity of growth hormone. Deficiency leads to stunted growth, delayed sexual maturation (hypogonadism), impaired wound healing, and cell-mediated immune dysfunction. A specific genetic defect in zinc absorption leads to **Acrodermatitis Enteropathica**, characterized by periorificial and acral dermatitis. **Analysis of Incorrect Options:** * **Vitamin A:** Deficiency typically presents with ocular symptoms (Xerophthalmia, Night blindness/Nyctalopia) and Bitot’s spots, not hypogonadism. * **Folic Acid:** Deficiency leads to Megaloblastic anemia and neural tube defects in newborns, but does not cause alopecia or hypogonadism. * **Cholecalciferol (Vitamin D):** Deficiency leads to Rickets in children (characterized by bone deformities like bow legs and rachitic rosary) and Osteomalacia in adults. **NEET-PG High-Yield Pearls:** * **Acrodermatitis Enteropathica:** An autosomal recessive disorder of the *SLC39A4* gene causing severe zinc malabsorption. * **Zinc & Insulin:** Zinc is required for the storage of insulin in the β-cells of the pancreas. * **Wound Healing:** Zinc is a cofactor for collagenase, making it vital for tissue repair.

Q: Which of the following is NOT a biological antioxidant that acts against free radicals formed inside the body?

Glycine. **Explanation:** The body utilizes a complex defense system of **antioxidants** to neutralize reactive oxygen species (ROS) and free radicals, preventing oxidative stress and cellular damage. **Why Glycine is the correct answer:** Glycine is a non-essential amino acid. While it is a structural component of **Glutathione** (a major intracellular antioxidant), glycine itself does not possess the chemical properties to directly scavenge free radicals or act as a cofactor for antioxidant enzymes. Therefore, it is not classified as a biological antioxidant. **Analysis of incorrect options:** * **Selenium (Option A):** This is an essential trace element that acts as a vital cofactor for **Glutathione Peroxidase**, an enzyme that neutralizes hydrogen peroxide into water. * **Uric acid (Option C):** Often overlooked, uric acid is a potent endogenous antioxidant in human plasma. It accounts for over half of the total antioxidant capacity of blood by scavenging hydroxyl radicals and singlet oxygen. * **Ascorbic acid (Option D):** Also known as Vitamin C, it is a powerful water-soluble antioxidant. It directly neutralizes free radicals and is essential for regenerating Vitamin E (Tocopherol) from its oxidized form. **High-Yield NEET-PG Pearls:** * **Enzymatic Antioxidants:** Superoxide Dismutase (SOD - requires Zn, Cu, or Mn), Catalase (requires Heme/Iron), and Glutathione Peroxidase (requires Selenium). * **Non-Enzymatic Antioxidants:** Vitamin E (chain-breaking), Vitamin C, Vitamin A (Beta-carotene), Glutathione, and Bilirubin. * **Glutathione (GSH):** A tripeptide made of **Glutamate, Cysteine, and Glycine**. Cysteine provides the active -SH (sulfhydryl) group responsible for its antioxidant action.

Q: All the following affect the absorption of calcium, EXCEPT?

Retinoic acid. **Explanation:** Calcium absorption occurs primarily in the duodenum and jejunum via active transport (regulated by Vitamin D) and passive diffusion. The efficiency of this process is significantly influenced by dietary factors that either enhance or inhibit its solubility. **Why Retinoic Acid is the correct answer:** Retinoic acid is a metabolite of **Vitamin A**. While Vitamin A is essential for bone remodeling and osteoblast activity, it does **not** directly influence the intestinal absorption of calcium. In contrast, **Vitamin D (Calcitriol)** is the primary fat-soluble vitamin responsible for increasing calcium absorption by inducing the synthesis of Calbindin in intestinal mucosal cells. **Analysis of Incorrect Options:** * **Citric acid:** This is an **enhancer** of calcium absorption. Organic acids like citrate and ascorbate form soluble complexes with calcium, preventing it from precipitating and making it more available for absorption. * **Phytates:** Found in cereal grains, phytates are **inhibitors**. They form insoluble calcium-phytate complexes in the gut, which cannot be absorbed, leading to decreased bioavailability. * **Oxalates:** Found in spinach, rhubarb, and beets, oxalates are potent **inhibitors**. They bind to calcium to form insoluble calcium oxalate crystals, which are excreted in the feces. **Clinical Pearls for NEET-PG:** * **Promoters of Calcium Absorption:** Vitamin D, PTH, acidic pH (gastric HCl), lactose, and amino acids (Lysine and Arginine). * **Inhibitors of Calcium Absorption:** Phytates, oxalates, high dietary phosphate (decreases solubility), malabsorption syndromes (steatorrhea), and alkaline pH. * **High-Yield Fact:** The most active form of Vitamin D, **1,25-dihydroxycholecalciferol**, acts via nuclear receptors to increase the expression of **TRPV6** (calcium channels) and **Calbindin-D9k**.

Q: What is the recommended nitrogen to caloric ratio in total parenteral nutrition?

1 gm of N2: 150 non-protein calories. ### Explanation **The Concept of Nitrogen-Calorie Ratio** In Total Parenteral Nutrition (TPN), the goal is to provide adequate energy (calories) so that the administered amino acids are used for protein synthesis (anabolism) rather than being oxidized for energy. This is known as the **"Protein Sparing Action"** of carbohydrates and fats. The standard recommended ratio for a stable, non-stressed patient is **1 gm of Nitrogen for every 150 non-protein calories (NPC)**. * **Calculation Note:** Since 6.25 gm of protein contains approximately 1 gm of nitrogen, this ratio ensures that the body has enough non-protein energy (from glucose and lipids) to efficiently utilize the protein provided. **Analysis of Options:** * **Option A (Correct):** 1:150 is the gold standard ratio for maintenance in stable patients to achieve a positive nitrogen balance. * **Option B & C:** These ratios (1:100 or 1.25:100) represent a higher nitrogen density. While these may be used in **hypermetabolic states** (e.g., severe burns, sepsis, or multi-trauma) where protein requirements are significantly elevated, they are not the standard recommended baseline ratio. * **Option D:** This is a distractor; Potassium (K) requirements are calculated based on milliequivalents (mEq) per liter or per kcal, not as a primary ratio for nitrogen balance. **High-Yield Clinical Pearls for NEET-PG:** 1. **Nitrogen Content:** To convert protein (gm) to Nitrogen (gm), divide by **6.25**. 2. **Non-Protein Calories:** Only calories from Carbohydrates (3.4 kcal/g in TPN) and Fats (9 kcal/g) are counted in this ratio. 3. **Stress Levels:** * Normal/Stable: 1:150 * Moderately Stressed: 1:100 to 1:120 * Severely Stressed: 1:80 4. **Respiratory Quotient (RQ):** If the NPC ratio is too high in carbohydrates, the RQ increases (>1.0), which can make weaning from a ventilator difficult due to increased $CO_2$ production.

Q: Which amino acid is the limiting amino acid in Bengal gram?

Methionine. ### Explanation **1. Why Methionine is Correct:** In nutritional biochemistry, a **limiting amino acid** is the essential amino acid found in the shortest supply relative to the body's requirements in a specific food source. * **Pulses and Legumes** (including Bengal gram/Chickpea) are rich in Lysine but characteristically **deficient in sulfur-containing amino acids**, specifically **Methionine** and Cysteine. * Therefore, Methionine is the primary limiting amino acid in Bengal gram. **2. Analysis of Incorrect Options:** * **B. Lysine:** This is the limiting amino acid in **Cereals** (like wheat, rice, and maize). Pulses are actually used to supplement cereal-based diets because they are rich in Lysine. * **C. Leucine:** While present in various quantities, it is rarely the "limiting" factor in common plant proteins. However, an excess of Leucine in Jowar (Sorghum) can interfere with Tryptophan metabolism, leading to Pellagra. * **D. Tryptophan:** This is the limiting amino acid in **Maize** (along with Lysine). **3. High-Yield Clinical Pearls for NEET-PG:** * **Mutual Supplementation:** To achieve a "complete protein" profile, cereals (deficient in Lysine) and pulses (deficient in Methionine) are consumed together (e.g., Dal-Chawal or Khichdi). * **Limiting Amino Acid Summary Table:** * **Pulses/Legumes:** Methionine * **Cereals:** Lysine * **Maize:** Tryptophan and Lysine * **Egg/Milk:** No limiting amino acids (Reference proteins with Biological Value of 100 and 95 respectively). * **Biological Value (BV):** Pulses generally have a lower BV (~60) compared to animal proteins due to these limiting amino acids.

Q: Endemic cardiomyopathy in children is linked to the deficiency of which trace element?

Selenium. **Explanation:** The correct answer is **Selenium**. Endemic cardiomyopathy, specifically known as **Keshan Disease**, is a congestive cardiomyopathy primarily affecting children and young women in regions of China where the soil is severely deficient in selenium. **Why Selenium is Correct:** Selenium is a vital component of the enzyme **Glutathione Peroxidase**, which protects cardiomyocytes from oxidative damage by neutralizing free radicals. In its absence, oxidative stress leads to myocardial necrosis and fibrosis. While selenium deficiency is the primary trigger, it is often associated with a secondary viral trigger (like Coxsackievirus B). **Why Other Options are Incorrect:** * **Zinc:** Deficiency typically presents as **Acrodermatitis Enteropathica** (periorificial rashes), growth retardation, impaired wound healing, and immune dysfunction, rather than cardiomyopathy. * **Cobalt:** While cobalt toxicity can cause "Beer-drinker's cardiomyopathy," its deficiency is not linked to endemic heart disease. Cobalt is a core component of Vitamin B12. * **Chromium:** Deficiency is rare but is associated with **impaired glucose tolerance** (insulin resistance) and peripheral neuropathy, as chromium enhances insulin action. **High-Yield Clinical Pearls for NEET-PG:** * **Keshan Disease:** Selenium deficiency + Cardiomyopathy. * **Kashin-Beck Disease:** Selenium deficiency + Osteoarthropathy (cartilage degeneration). * **Total Parenteral Nutrition (TPN):** Long-term TPN without supplementation is a common modern cause of selenium deficiency. * **Glutathione Peroxidase:** The key antioxidant enzyme requiring Selenium as a cofactor.

Q: The most frequent trace mineral deficiency developing in a patient receiving parenteral alimentation is a deficiency of which mineral?

Zinc. **Explanation:** The correct answer is **Zinc**. Total Parenteral Nutrition (TPN) solutions, unless specifically supplemented, often lack adequate trace minerals. Zinc is the most common trace mineral deficiency in this setting because it is primarily absorbed in the small intestine and has significant losses through gastrointestinal secretions. Patients on TPN often have underlying malabsorption or chronic diarrhea, which further depletes zinc stores. **Why the other options are incorrect:** * **Calcium:** While electrolyte imbalances are common in TPN, calcium is a macro-mineral, not a trace mineral. It is routinely added to TPN formulations in significant quantities. * **Chromium:** Chromium deficiency can occur during long-term TPN and manifests as glucose intolerance (insulin resistance), but it is statistically much rarer than zinc deficiency. * **Cobalt:** Cobalt is a constituent of Vitamin B12. Isolated cobalt deficiency is not clinically recognized in humans; deficiency manifests as Vitamin B12 deficiency. **High-Yield Clinical Pearls for NEET-PG:** * **Zinc Deficiency Presentation:** Look for **Acrodermatitis Enteropathica** (periorificial and acral dermatitis), alopecia, diarrhea, impaired wound healing, and hypogeusia (decreased taste). * **Copper Deficiency:** The second most common trace mineral deficiency in TPN; presents with **microcytic anemia** (refractory to iron) and neutropenia. * **Selenium Deficiency:** Can lead to **Keshan disease** (cardiomyopathy) or skeletal muscle pain. * **Manganese/Copper Caution:** These are excreted via bile; they should be restricted in patients with obstructive jaundice to prevent toxicity.

Q: Which amino acid is deficient in rice?

Lysine. ### Explanation **Core Concept: Limiting Amino Acids in Cereals** In nutritional biochemistry, a "limiting amino acid" is the essential amino acid found in the smallest quantity in a specific food source, thereby limiting the body's ability to synthesize proteins. Cereals (like rice, wheat, and maize) are generally characterized by a deficiency in **Lysine**. **Why Option A is Correct:** Rice is a cereal grain. All cereals are deficient in the essential amino acid **Lysine**, but they are relatively rich in sulfur-containing amino acids like Methionine and Cysteine. Therefore, to achieve a "complete protein" profile, rice is traditionally consumed with pulses (dal), which are rich in Lysine but deficient in Methionine. **Why Other Options are Incorrect:** * **B. Methionine:** This is the limiting amino acid in **pulses/legumes**. Rice actually contains adequate amounts of Methionine, making it the perfect complementary protein source for lentils. * **C. Glutamic acid:** This is a non-essential amino acid and is generally abundant in most dietary proteins; it is not a limiting factor in rice. * **D. Tryptophan:** This is the classic limiting amino acid in **Maize (Corn)**. A diet solely based on maize can lead to Pellagra because Tryptophan is a precursor for Niacin (Vitamin B3) synthesis. **High-Yield NEET-PG Pearls:** 1. **Cereals:** Deficient in Lysine; Rich in Methionine. 2. **Pulses:** Deficient in Methionine; Rich in Lysine. 3. **Maize:** Deficient in both Lysine and Tryptophan. 4. **Reference Protein:** Egg albumin is considered the "standard" or reference protein (Biological Value = 100) against which other proteins are compared. 5. **Mutual Supplementation:** The practice of mixing cereals and pulses (e.g., Khichdi or Idli) ensures all essential amino acids are present, improving the overall **Net Protein Utilization (NPU)**.

Question 1

Which of the following caseins predominates in cow milk?

Accepted Answer

alpha-casein

Answer

beta-casein

Answer

Equally present

Answer

None of the above

Question 2

Chromium deficiency may lead to which of the following?

Accepted Answer

Insulin dysfunction

Answer

Cardiomyopathy

Answer

Endocarditis

Answer

External ophthalmoplegia

Question 3

A child presents with growth retardation, hypogonadism, alopecia, and immunodeficiency. The child has a deficiency of which of the following nutrients?

Accepted Answer

Zinc

Answer

Vitamin A

Answer

Folic Acid

Answer

Cholecalciferol

Question 4

Which of the following is NOT a biological antioxidant that acts against free radicals formed inside the body?

Accepted Answer

Glycine

Answer

Selenium

Answer

Uric acid

Answer

Ascorbic acid

Question 5

All the following affect the absorption of calcium, EXCEPT?

Accepted Answer

Retinoic acid

Answer

Citric acid

Answer

Phytates

Answer

Oxalates

Question 6

What is the recommended nitrogen to caloric ratio in total parenteral nutrition?

Accepted Answer

1 gm of N2: 150 non-protein calories

Answer

1 gm of N2: 100 non-protein calories

Answer

1.25 gm of N2: 100 non-protein calories

Answer

1.25 gm of K: 150 non-protein calories

Question 7

Which amino acid is the limiting amino acid in Bengal gram?

Accepted Answer

Methionine

Answer

Lysine

Answer

Leucine

Answer

Tryptophan

Question 8

Endemic cardiomyopathy in children is linked to the deficiency of which trace element?

Accepted Answer

Selenium

Answer

Zinc

Answer

Cobalt

Answer

Chromium

Question 9

The most frequent trace mineral deficiency developing in a patient receiving parenteral alimentation is a deficiency of which mineral?

Accepted Answer

Zinc

Answer

Calcium

Answer

Chromium

Answer

Cobalt

Question 10

Which amino acid is deficient in rice?

Accepted Answer

Lysine

Answer

Methionine

Answer

Glutamic acid

Answer

Tryptophan

Nutrition and Metabolism — MCQs

Nutrition and Metabolism — MCQs

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