UPSC-CMS 2025 - Biochemistry PYQs Practice Questions

Q: A 36 year old man presents with decreased appetite, mouth soreness, diarrhoea and irritability. On examination he has a bright red tongue with a pigmented scaly rash around the neck. Which one of the following food items in his diet has a bearing on his disease?

Corn. ***Corn*** - A diet heavily reliant on **corn** (maize) as a staple lacking proper fortification or preparation can lead to **niacin (Vitamin B3) deficiency**, historically common in regions where corn was the primary dietary component. - The symptoms described—**decreased appetite, mouth soreness, diarrhea, irritability, bright red tongue (glossitis)**, and a **pigmented scaly rash around the neck (Casal's necklace)**—are classic manifestations of **pellagra**, a disease caused by niacin deficiency. *Wheat* - While wheat is a common dietary staple, it is not typically associated with classic pellagra symptoms like **Casal's necklace** or severe **glossitis** that point specifically to niacin deficiency. - Wheat-related issues usually involve **celiac disease** (gluten intolerance) or other sensitivities, presenting with different gastrointestinal and dermatological profiles. *Fish* - Fish is a good source of various nutrients, including some B vitamins, and is generally not associated with causing nutritional deficiencies like pellagra. - No symptoms described are typically linked to a diet rich in fish or lack thereof in a way that points to the given presentation. *Rice* - Rice can be a staple food, but a diet predominantly of polished rice can lead to **thiamine (Vitamin B1) deficiency** causing **beriberi**, which presents differently (e.g., neuropathy, heart failure). - It does not cause the characteristic dermatological signs of pellagra like **Casal's necklace**. [Practice more Biochemistry PYQs on OnCourse]

Q: Acrodermatitis enteropathica is an autosomal recessive metabolic disorder which affects the absorption of which one of the following micronutrients?

Zinc. ***Correct: Zinc*** - **Acrodermatitis enteropathica** is an autosomal recessive disorder caused by a defect in the absorption of **zinc** from the intestines (due to mutations in the *SLC39A4* gene encoding the ZIP4 zinc transporter). - This leads to the characteristic clinical triad: periorificial and acral **dermatitis**, **alopecia**, and **diarrhea**. - Treatment involves lifelong zinc supplementation. *Incorrect: Selenium* - **Selenium** deficiency can lead to **Keshan disease** (cardiomyopathy) and **Kashin-Beck disease** (osteoarthropathy), which are distinct from acrodermatitis enteropathica. - Symptoms related to selenium deficiency do not typically include the prominent dermatological and gastrointestinal features seen in acrodermatitis enteropathica. *Incorrect: Iron* - **Iron** deficiency primarily causes **anemia** and symptoms like fatigue, pallor, and pica. - While iron is a crucial micronutrient, its malabsorption does not result in the specific skin, hair, and gastrointestinal manifestations of acrodermatitis enteropathica. *Incorrect: Iodine* - **Iodine** deficiency is strongly associated with **goiter** and various thyroid dysfunctions, including **hypothyroidism** and **cretinism**. - These conditions are entirely different from the syndrome of acrodermatitis enteropathica, which is characterized by zinc malabsorption. [Practice more Biochemistry PYQs on OnCourse]

Q: Which one of the following is the major contributor to the total energy intake, in terms of energy provided, in an average Indian diet?

Carbohydrates. ***Carbohydrates*** - **Carbohydrates** are the primary source of energy in an average Indian diet, mainly from staple foods like rice, wheat, and millets. - They provide approximately **4 kcal/gram** and constitute the bulk of daily caloric intake for most individuals in India. *Proteins* - While essential for growth and repair, **proteins** are typically consumed in smaller quantities than carbohydrates in the average Indian diet. - They provide about **4 kcal/gram**, but total protein intake often contributes less to overall energy compared to carbohydrates. *Fats* - **Fats** are the most energy-dense macronutrient, providing **9 kcal/gram**, but their overall contribution to total energy intake is usually less than that of carbohydrates. - The typical Indian diet emphasizes carbohydrate-rich vegetarian staples, with fats often used for cooking rather than forming the primary energy source. *Vitamins* - **Vitamins** are micronutrients essential for various bodily functions and do not provide any direct energy (calories). - They are crucial for metabolic processes but are not considered a source of energy intake. [Practice more Biochemistry PYQs on OnCourse]

Q: Consider the following with regard to Amino Acids : I. Essential Amino Acids are those that the body cannot synthesize and they must be obtained from dietary proteins. II. Not just the Essential Amino Acids, Non-essential Amino Acids are also needed by the body for synthesis of tissue proteins. III. Unless a protein contains all the Essential Amino Acids in amounts corresponding to human needs, a protein is said to be biologically incomplete. IV. Animal proteins are rated superior to vegetable proteins. Of the above statements, how many are correct?

All four. ***All four*** - **Statement I is correct:** Essential amino acids cannot be synthesized by the body and must be obtained from dietary sources. The 9 essential amino acids include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. - **Statement II is correct:** Both essential and non-essential amino acids are required for tissue protein synthesis. Non-essential amino acids (like alanine, aspartic acid, glutamic acid, etc.) are equally important for building proteins, even though the body can synthesize them. - **Statement III is correct:** A protein is considered **biologically incomplete** if it lacks one or more essential amino acids in adequate amounts. Complete proteins contain all essential amino acids in proportions that meet human nutritional requirements. - **Statement IV is correct:** Animal proteins (meat, fish, eggs, dairy) are traditionally rated as superior to most plant proteins because they are **complete proteins** containing all essential amino acids in adequate proportions with high biological value. Most plant proteins (except soy, quinoa) are incomplete or limiting in one or more essential amino acids. Since all four statements (I, II, III, and IV) are factually correct, the answer is **all four**. *Only three* - This option is incorrect because all four statements about amino acids are medically accurate, not just three of them. *Only two* - This option is incorrect as it significantly underestimates the number of correct statements. All four statements are valid principles in biochemistry and nutrition. *Only one* - This option is incorrect as multiple statements are correct. All four statements represent established knowledge about protein nutrition and amino acid classification. [Practice more Biochemistry PYQs on OnCourse]

Q: Dietary fibres have :

no metabolic effect. ***no metabolic effect*** - Dietary fibers are **indigestible polysaccharides** that cannot be broken down by human digestive enzymes. - Humans lack enzymes like **cellulase** necessary to hydrolyze the β-glycosidic bonds in dietary fiber. - Dietary fibers pass through the gastrointestinal tract **without being metabolized** by human cells, meaning they do not participate in anabolic or catabolic pathways. - While gut bacteria can ferment some fibers producing short-chain fatty acids (SCFAs), this is **bacterial metabolism**, not human metabolism. - The physiological effects of fiber (improved bowel motility, reduced cholesterol absorption, glycemic control) are **mechanical and physicochemical**, not metabolic. *catabolic effect* - Catabolic processes involve **breakdown of molecules with energy release** (e.g., glycolysis, lipolysis). - Dietary fibers cannot undergo catabolism in humans because we lack the enzymes to break them down. - The fermentation by gut bacteria is not human catabolism. *anabolic effect* - Anabolic processes involve **synthesis of complex molecules** from simpler ones (e.g., protein synthesis, glycogenesis). - Dietary fibers are not absorbed or incorporated into human tissues, so they cannot participate in anabolic reactions. *sometimes anabolic and sometimes catabolic effect, depending on the type* - Regardless of fiber type (soluble or insoluble), **all dietary fibers remain non-metabolizable** by human enzymes. - Neither type undergoes anabolic or catabolic metabolism in human cells. [Practice more Biochemistry PYQs on OnCourse]

Question 1

A 36 year old man presents with decreased appetite, mouth soreness, diarrhoea and irritability. On examination he has a bright red tongue with a pigmented scaly rash around the neck. Which one of the following food items in his diet has a bearing on his disease?

Accepted Answer

Corn

Answer

Wheat

Answer

Fish

Answer

Rice

Question 2

Acrodermatitis enteropathica is an autosomal recessive metabolic disorder which affects the absorption of which one of the following micronutrients?

Accepted Answer

Zinc

Answer

Selenium

Answer

Iron

Answer

Iodine

Question 3

Which one of the following is the major contributor to the total energy intake, in terms of energy provided, in an average Indian diet?

Accepted Answer

Carbohydrates

Answer

Proteins

Answer

Fats

Answer

Vitamins

Question 4

Consider the following with regard to Amino Acids :
I. Essential Amino Acids are those that the body cannot synthesize and they must be obtained from dietary proteins.
II. Not just the Essential Amino Acids, Non-essential Amino Acids are also needed by the body for synthesis of tissue proteins.
III. Unless a protein contains all the Essential Amino Acids in amounts corresponding to human needs, a protein is said to be biologically incomplete.
IV. Animal proteins are rated superior to vegetable proteins.

Of the above statements, how many are correct?

Accepted Answer

All four

Answer

Only two

Answer

Only three

Answer

Only one

Question 5

Dietary fibres have :

Accepted Answer

no metabolic effect

Answer

catabolic effect

Answer

sometimes anabolic and sometimes catabolic effect, depending on the type

Answer

anabolic effect

Question 6

Egg proteins are considered to be the best among food proteins because :
I. of their biological value
II. of their digestibility
III. they contain all the essential amino acids
IV. their calorie content is higher than in proteins of vegetable sources

Which of the statements given above is/are correct?

Accepted Answer

I, II and III

Answer

II, III and IV

Answer

I only

Answer

I, III and IV

Question 7

Which one among the following essential amino acids is usually the "limiting" amino acid in most of the pulses?

Accepted Answer

Methionine

Answer

Valine

Answer

Threonine

Answer

Lysine

UPSC-CMS 2025 — Biochemistry