Nutrition and Metabolism Practice Questions

Q: Which of the following is NOT a trace element required for human nutrition?

Zinc (Zn). **Explanation:** The classification of minerals in human nutrition is based on the daily dietary requirement. Minerals are divided into **Macro-minerals** (required in amounts >100 mg/day) and **Micro-minerals/Trace elements** (required in amounts <100 mg/day). **Why Zinc (Zn) is the correct answer:** Zinc is classified as a **trace element**. The average adult requirement for Zinc is approximately 8–11 mg/day. It serves as a vital cofactor for over 300 enzymes, including Carbonic Anhydrase, Alcohol Dehydrogenase, and DNA/RNA polymerases. Since the question asks which of the following is a trace element (noting the checkmark provided in the prompt), Zinc fits this classification perfectly. **Analysis of Incorrect Options (Macro-minerals):** * **Magnesium (Mg):** A macro-mineral required in amounts of ~300–400 mg/day. It is essential for ATP-related reactions and bone structure. * **Calcium (Ca):** The most abundant mineral in the body and a major macro-mineral. The RDA is ~1000 mg/day. * **Potassium (K):** The primary intracellular cation and a macro-mineral. The daily requirement is high (~3500–4700 mg/day) to maintain membrane potential. **High-Yield Clinical Pearls for NEET-PG:** * **Ultra-trace elements:** Required in <1 mg/day (e.g., Selenium, Manganese, Molybdenum). * **Zinc Deficiency:** Characterized by **Acrodermatitis enteropathica**, poor wound healing, hypogeusia (decreased taste), and growth retardation. * **Zinc Fingers:** These are structural motifs in proteins that help in binding DNA, crucial for steroid hormone receptor function. * **Chromium:** A trace element essential for insulin action (Glucose Tolerance Factor).

Q: Which protein is known as the reference protein?

Milk. **Explanation:** The concept of a **Reference Protein** refers to a protein that contains all essential amino acids in the optimal proportions required by the human body for growth and maintenance. **Why Milk is the Correct Answer:** In nutritional biochemistry, **Milk protein (specifically Egg protein and Milk protein)** is considered a reference protein because it has a high biological value (BV) and a Net Protein Utilization (NPU) score near 100. These proteins are almost completely absorbed and utilized by the body. While Egg is often cited as the "gold standard" reference protein in many textbooks, **Milk** is the correct choice among the given options as it provides a complete amino acid profile with high bioavailability. **Analysis of Incorrect Options:** * **B. Soyabean:** Although it is the richest plant source of protein, it is deficient in sulfur-containing amino acids like **Methionine**. Plant proteins are generally "incomplete" compared to animal sources. * **C. Orange:** Oranges are primarily a source of Vitamin C and carbohydrates; their protein content is negligible. * **D. Potato:** While potatoes contain high-quality protein (Tuberin), the total quantity is too low (approx. 2%) to serve as a primary reference source. **High-Yield NEET-PG Pearls:** * **Biological Value (BV):** Measures the proportion of absorbed protein retained in the body. Egg has a BV of 100. * **Limiting Amino Acids:** Pulses are deficient in **Methionine**, while Cereals are deficient in **Lysine**. * **Mutual Supplementation:** Combining cereals and pulses (e.g., Khichdi) provides a complete amino acid profile, a concept frequently tested in community medicine and biochemistry. * **Reference Protein Standard:** The FAO/WHO often uses the amino acid composition of **Egg or Milk** as the benchmark to calculate the "Chemical Score" of other foods.

Q: What is the major mineral component of bone?

Hydroxyapatite. **Explanation:** The correct answer is **Hydroxyapatite**. Bone is a specialized connective tissue consisting of an organic matrix (primarily Type I collagen) and an inorganic mineral phase. The mineral component accounts for approximately 65-70% of bone weight and is primarily composed of a crystalline form of calcium phosphate known as **Hydroxyapatite**, with the chemical formula **$\text{Ca}_{10}(\text{PO}_4)_6(\text{OH})_2$**. These crystals align along collagen fibers to provide the skeleton with its characteristic compressive strength and structural rigidity. **Analysis of Options:** * **Calcite (A):** This is a stable polymorph of calcium carbonate found in the shells of marine organisms and limestone, but it is not a biological component of human bone. * **Calcium oxide (C):** Also known as quicklime, this is a caustic chemical used in industrial processes. It does not occur naturally in human tissues. * **Calcium carbonate (D):** While small amounts of carbonate are incorporated into the hydroxyapatite lattice as impurities, pure calcium carbonate is the primary component of eggshells and antacid tablets, not the structural mineral of bone. **High-Yield Clinical Pearls for NEET-PG:** * **Mineralization:** The process of depositing hydroxyapatite into the organic matrix is regulated by **alkaline phosphatase**, which increases local phosphate concentrations. * **Fluorosis:** Fluoride ions can replace the hydroxyl (-OH) groups in hydroxyapatite to form **Fluoroapatite**, which is more resistant to acid dissolution (relevant in dental caries prevention). * **Vitamin D:** Essential for bone health as it maintains the calcium-phosphorus product necessary for the crystallization of hydroxyapatite. * **Bone Reservoir:** Hydroxyapatite serves as the body’s primary reservoir for calcium (99%) and phosphorus (85%).

Q: In marasmus, wasting is due to which of the following?

All of the above. **Explanation:** Marasmus is a form of severe protein-energy malnutrition (PEM) characterized by a global deficiency of nutrients. The underlying pathophysiology involves a state of negative energy balance where the body adapts to starvation. 1. **Why Option D is correct:** Marasmus results from a **prolonged deficiency of both calories (energy) and protein (Option A & B)**. Unlike Kwashiorkor, where protein deficiency is disproportionately greater than calorie intake, Marasmus is "balanced" starvation. To compensate for the lack of exogenous fuel, the body enters a hypercatabolic state. It mobilizes endogenous stores, leading to the **excess catabolism of subcutaneous fat and skeletal muscle (Option C)** to provide amino acids for gluconeogenesis and fatty acids for energy. This results in the characteristic "skin and bones" appearance. 2. **Analysis of Options:** * **Option A & B:** These are the primary triggers. While Kwashiorkor is classically "Protein deficiency with adequate calories," Marasmus is "Total calorie deficiency." * **Option C:** This is the physiological mechanism of wasting. The body sacrifices muscle mass to maintain blood glucose levels for vital organ function. **High-Yield Clinical Pearls for NEET-PG:** * **Appearance:** "Old man's face" or "Monkey-like facies" due to loss of buccal pads of fat. * **Edema:** Absent in Marasmus (present in Kwashiorkor due to hypoalbuminemia). * **Growth:** Severe growth retardation and "baggy pants" appearance (loose skin folds over buttocks). * **Key Difference:** Marasmus = Starvation (Calorie + Protein); Kwashiorkor = Protein deficiency + Stress/Infection.

Q: A patient receiving total parenteral nutrition is at risk of developing which of the following nutrient deficiencies?

Zinc. **Explanation:** **Correct Option: D (Zinc)** Patients on Total Parenteral Nutrition (TPN) are at a high risk of trace element deficiencies, most notably **Zinc**. Zinc is primarily absorbed in the small intestine; in TPN patients, the bypass of the gastrointestinal tract, coupled with increased urinary losses and high metabolic demands, leads to rapid depletion. * **Clinical Presentation:** Zinc deficiency in TPN patients typically manifests as **acrodermatitis enteropathica-like lesions** (periorificial and acral dermatitis), alopecia, impaired wound healing, and altered taste (hypogeusia). **Why Incorrect Options are Wrong:** * **A & B (Vitamin B12 and Folic Acid):** These are water-soluble vitamins that are standard components of routine parenteral multivitamin formulations (e.g., MVI-12). While B12 stores in the liver can last for years, folate stores last for months; however, acute deficiency is rare in TPN unless they are omitted from the daily infusion. * **C (Vitamin B6):** Pyridoxine is also routinely supplemented in TPN solutions. Isolated deficiency is uncommon compared to the rapid onset of trace element depletion like Zinc. **NEET-PG High-Yield Pearls:** * **Most common trace element deficiency in TPN:** Zinc. * **Chromium deficiency in TPN:** Presents as **glucose intolerance** (insulin resistance) because chromium is a component of the Glucose Tolerance Factor. * **Copper deficiency in TPN:** Presents as microcytic anemia and neutropenia (resembling Vitamin B12 deficiency but with normal B12 levels). * **Selenium deficiency in TPN:** Can lead to **cardiomyopathy** (Keshan-like disease) and muscle pain.

Q: Which amino acid is considered limiting in soybeans?

Methionine. ### Explanation The concept of a **limiting amino acid** refers to the essential amino acid present in the lowest quantity relative to the body's requirements in a specific protein source. This deficiency limits the body's ability to synthesize new proteins, even if other amino acids are abundant. **Why Methionine is the correct answer:** Soybeans are a high-quality plant protein source, but like most **legumes (pulses)**, they are deficient in sulfur-containing amino acids, specifically **Methionine** and Cysteine. To achieve a "complete protein" profile, legumes are often paired with cereals (like rice or wheat), which are rich in methionine but deficient in lysine. **Analysis of Incorrect Options:** * **A. Threonine:** This is the limiting amino acid in certain grains like rice (along with lysine), but it is present in adequate amounts in soy. * **B. Lysine:** This is the classic limiting amino acid in **cereals** (wheat, maize, rice). Soybeans are actually rich in lysine, which is why soy-flour is often used to fortify wheat flour. * **C. Tryptophan:** This is the limiting amino acid in **Maize (Corn)**. A deficiency of tryptophan (a precursor to Niacin) leads to Pellagra. **High-Yield Clinical Pearls for NEET-PG:** * **Pulses/Legumes:** Limiting amino acid is **Methionine**. * **Cereals:** Limiting amino acid is **Lysine**. * **Maize:** Limiting amino acids are **Lysine and Tryptophan**. * **Mutual Supplementation:** The practice of combining cereals and pulses (e.g., Dal-Chawal) to provide all essential amino acids is known as the **supplementary action of proteins**. * **Reference Protein:** Egg albumin is considered the "standard" or reference protein (Biological Value = 100) as it contains all essential amino acids in ideal proportions.

Q: Maize is deficient in which of the following amino acids?

Lysine. ### Explanation The correct answer is **B. Lysine**. **Underlying Concept:** In nutrition, "limiting amino acids" are essential amino acids found in the shortest supply relative to the body's requirements. Most cereals are deficient in **Lysine**, while legumes (pulses) are typically deficient in **Methionine**. Maize (corn) is a classic example of a cereal that is deficient in both **Lysine and Tryptophan**. **Analysis of Options:** * **Lysine (Correct):** Maize proteins (zein) are notoriously low in lysine. This is why populations relying solely on maize as a staple food are at risk for protein-energy malnutrition. * **Methionine (Incorrect):** Methionine is the limiting amino acid in **pulses/legumes**. Cereals like maize actually contain adequate amounts of sulfur-containing amino acids like methionine. * **Leucine (Incorrect):** Maize is actually **rich in Leucine**. In fact, an excess of leucine in maize interferes with the conversion of tryptophan to niacin (Vitamin B3), which can contribute to the development of **Pellagra**. **Clinical Pearls & High-Yield Facts for NEET-PG:** 1. **Pellagra and Maize:** Maize is deficient in Tryptophan (a precursor for Niacin) and contains Niacin in a bound, unabsorbable form (niacytin). The high Leucine content further inhibits Niacin synthesis, making maize-eaters highly susceptible to Pellagra (the 4 D's: Dermatitis, Diarrhea, Dementia, Death). 2. **Mutual Supplementation:** To achieve a "complete protein" profile, cereals (deficient in lysine) should be consumed with pulses (deficient in methionine). 3. **Limiting Amino Acids Summary:** * **Wheat/Rice/Maize:** Lysine * **Pulses:** Methionine * **Egg/Milk:** None (Reference proteins)

Q: Maize is deficient in which amino acid?

Tryptophan. **Explanation:** The correct answer is **Tryptophan**. Maize (corn) is a cereal grain that is notoriously deficient in two essential amino acids: **Tryptophan** and **Lysine**. **Why Tryptophan is the Correct Answer:** In biochemistry and nutrition, the "limiting amino acid" is the one present in the lowest quantity relative to human requirements. Maize proteins (zein) are severely lacking in Tryptophan. This deficiency is clinically significant because Tryptophan is the metabolic precursor for **Niacin (Vitamin B3)**. A diet solely dependent on maize leads to a secondary deficiency of Niacin, resulting in the clinical condition known as **Pellagra**. **Analysis of Incorrect Options:** * **A. Leucine:** Maize is actually **rich in Leucine**. High levels of Leucine are thought to interfere with the conversion of Tryptophan to Niacin by inhibiting the enzyme *quinolinate phosphoribosyltransferase (QPRT)*, further exacerbating the risk of Pellagra. * **B. Methionine:** This is the limiting amino acid in **pulses/legumes**. Cereals like maize are generally adequate in sulfur-containing amino acids like Methionine. * **D. Phenylalanine:** This is an essential amino acid that is generally present in sufficient quantities in most cereal proteins, including maize. **High-Yield Clinical Pearls for NEET-PG:** * **Pellagra Triad:** Dermatitis, Diarrhea, and Dementia (the 4th 'D' is Death). * **Limiting Amino Acids Mnemonic:** * **C**ereals are deficient in **L**ysine (C-L). * **P**ulses are deficient in **M**ethionine (P-M). * **Maize** is deficient in **T**ryptophan and **L**ysine. * **Niacytin:** The niacin present in maize is in a bound form called "Niacytin," which cannot be absorbed by the human gut unless treated with alkali (e.g., lime).

Q: Which of the following is not degraded by colonic flora?

Lignin. **Explanation:** The colonic flora consists of trillions of bacteria capable of fermenting various carbohydrates and fibers into short-chain fatty acids (SCFAs) like butyrate, acetate, and propionate. **Why Lignin is the correct answer:** Lignin is a complex, non-carbohydrate polymer of aromatic alcohols (phenylpropane units) found in the woody parts of plants. Unlike dietary fibers such as cellulose or pectin, **lignin is completely resistant to bacterial fermentation** in the human colon. It is technically not a polysaccharide, and its rigid structure cannot be broken down by human or microbial enzymes, making it the only option that remains entirely undegraded. **Analysis of Incorrect Options:** * **Pectin:** A soluble dietary fiber found in fruits. It is highly fermentable and is almost completely degraded by colonic bacteria. * **Starch:** While most starch is digested in the small intestine, "Resistant Starch" reaches the colon, where it is readily fermented by microflora. * **Glucose:** Although primarily absorbed in the small intestine, any glucose reaching the large intestine is rapidly utilized as an energy source by colonic bacteria. **High-Yield Clinical Pearls for NEET-PG:** * **Dietary Fiber Classification:** Fibers are divided into **Soluble** (Pectin, Gums, Mucilages) and **Insoluble** (Cellulose, Hemicellulose, Lignin). * **The Lignin Exception:** Lignin is the only major dietary fiber that is **not a polysaccharide**. * **Benefits of Fermentation:** Bacterial degradation of fiber produces **Butyrate**, which is the primary energy source for colonocytes and has anti-cancer properties. * **Laxative Effect:** Insoluble fibers like lignin and cellulose increase fecal bulk and decrease intestinal transit time, preventing constipation.

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.

Question 1

Which of the following is NOT a trace element required for human nutrition?

Accepted Answer

Zinc (Zn)

Answer

Magnesium (Mg)

Answer

Calcium (Ca)

Answer

Potassium (K)

Question 2

Which protein is known as the reference protein?

Accepted Answer

Milk

Answer

Soyabean

Answer

Orange

Answer

Potato

Question 3

What is the major mineral component of bone?

Accepted Answer

Hydroxyapatite

Answer

Calcite

Answer

Calcium oxide

Answer

Calcium carbonate

Question 4

In marasmus, wasting is due to which of the following?

Accepted Answer

All of the above

Answer

Prolonged dietary deficiency of calories

Answer

Prolonged dietary deficiency of protein

Answer

Excess catabolism of fat and muscle mass to provide energy

Question 5

A patient receiving total parenteral nutrition is at risk of developing which of the following nutrient deficiencies?

Accepted Answer

Zinc

Answer

Vitamin B12

Answer

Folic acid

Answer

Vitamin B6

Question 6

Which amino acid is considered limiting in soybeans?

Accepted Answer

Methionine

Answer

Threonine

Answer

Lysine

Answer

Tryptophan

Question 7

Maize is deficient in which of the following amino acids?

Accepted Answer

Lysine

Answer

Methionine

Answer

Leucine

Answer

All of the above

Question 8

Maize is deficient in which amino acid?

Accepted Answer

Tryptophan

Answer

Leucine

Answer

Methionine

Answer

Phenylalanine

Question 9

Which of the following is not degraded by colonic flora?

Accepted Answer

Lignin

Answer

Pectin

Answer

Starch

Answer

Glucose

Question 10

Which of the following caseins predominates in cow milk?

Accepted Answer

alpha-casein

Answer

beta-casein

Answer

Equally present

Answer

None of the above

Nutrition and Metabolism — MCQs

Nutrition and Metabolism — MCQs

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