UPSC-CMS 2012 — Biochemistry

Q: Consider the following statements: 1. Diets high in vitamin C have been claimed to lower the incidence of certain cancers, particularly oesophageal and gastric cancers. 2. Vitamin C can prevent the conversion of nitrites and secondary amines to carcinogenic nitrosamines. Which of the statements given above is/are correct?

Both 1 and 2. ***Both 1 and 2*** - **Statement 1 is correct:** Epidemiological studies have consistently shown that diets high in vitamin C are associated with a **lower incidence of oesophageal and gastric cancers**, attributed to its antioxidant properties and protective mechanisms. - **Statement 2 is correct:** Vitamin C acts as a **reducing agent that blocks nitrosamine formation** by preventing nitrites and secondary amines from reacting to form these carcinogenic compounds in the acidic gastric environment. - Both statements are **independently true and complementary** - statement 2 explains one of the key mechanisms by which statement 1's observation occurs. *1 only* - This option is incorrect because it ignores statement 2, which describes a **well-established biochemical mechanism** of vitamin C's cancer-protective effect. - The ability of vitamin C to prevent nitrosamine formation is a **proven protective mechanism**, not just a claim. *2 only* - This option is incorrect because it ignores statement 1, which accurately reflects **epidemiological evidence** linking high vitamin C intake with reduced cancer risk. - The association between dietary vitamin C and lower cancer incidence is **well-documented in observational studies**. *Neither 1 nor 2* - This option is completely incorrect as **both statements are scientifically accurate** and supported by substantial evidence. - Vitamin C's role in **cancer prevention through antioxidant activity and nitrosamine inhibition** is well-established in biochemistry and nutrition science. [Practice more Biochemistry PYQs on OnCourse]

Q: The biological value of a given protein depends upon

Digestibility and amino acid composition. ***Digestibility and amino acid composition*** - The **biological value (BV)** of a protein measures how efficiently the body can use the absorbed protein from a food source for growth and maintenance. - It is primarily determined by two factors: the **digestibility** of the protein (how much is absorbed) and its **amino acid composition** (the proportion and availability of essential amino acids). *Digestibility and leucine content* - While **digestibility** is an important factor for biological value, **leucine content** alone is not sufficient to determine it. - The biological value depends on the **overall balance of essential amino acids**, not just one specific amino acid. *Amino acid composition and specific dynamic effect* - **Amino acid composition** is crucial for biological value, but the **specific dynamic effect (SDE)**, also known as the thermic effect of food, refers to the energy expended during the digestion, absorption, and assimilation of food. - SDE is related to energy metabolism, not directly to the protein's utility for tissue synthesis. *Amino acid composition alone* - **Amino acid composition** is a key determinant, particularly the presence and proportion of **essential amino acids**. - However, for a protein to be utilized, it must first be **digested and absorbed**, making digestibility an equally critical factor affecting its overall biological value. [Practice more Biochemistry PYQs on OnCourse]

Q: Which one of the following vitamins given as a supplement during the peri-conceptional period to a woman can help prevent the neural tube defects in the baby ?

Folic acid. ***Folic acid*** - **Folic acid** (vitamin B9) supplementation is crucial during the **peri-conceptional period** to prevent neural tube defects. - Adequate folic acid intake helps in the proper development and closure of the **neural tube** in the embryo, which forms the brain and spinal cord. *Riboflavin* - **Riboflavin** (vitamin B2) is essential for energy metabolism and cellular growth but has no direct, established role in preventing neural tube defects. - Deficiency can lead to **ariboflavinosis**, characterized by skin lesions, but not directly linked to neural tube malformations. *Thiamine* - **Thiamine** (vitamin B1) is vital for carbohydrate metabolism and nerve function. - Its deficiency causes **beriberi** and neurological problems in adults, but it does not directly prevent neural tube defects. *Vitamin B12* - **Vitamin B12** (cobalamin) is important for DNA synthesis and nerve function, and it works closely with folate. - While B12 deficiency can lead to megaloblastic anemia and neurological issues, **folic acid** is the primary vitamin for preventing neural tube defects. [Practice more Biochemistry PYQs on OnCourse]

Q: Match List-I with List-II and select the correct answer using the code given below the Lists:

A→3 B→1 C→2 D→4. ***A→3 B→1 C→2 D→4*** - **Thiamine (Vitamin B1)** deficiency can lead to **beriberi**, which often manifests as **wet beriberi** characterized by **high-output cardiac failure**, edema, and peripheral neuropathy. - **Niacin (Vitamin B3)** deficiency causes **pellagra**, a disease classically presenting with the "4 Ds": **dermatitis**, diarrhea, dementia, and death. - **Retinol (Vitamin A)** deficiency is primarily known for causing **xerophthalmia**, which includes early signs like **night blindness** and later stages like Bitot's spots (foamy keratin debris on the conjunctiva) and keratomalacia. - **Cholecalciferol (Vitamin D)** deficiency leads to **rickets in children**, characterized by impaired bone mineralization causing skeletal deformities such as a **rachitic rosary** (enlargement of the costochondral junctions). *A→3 B→2 C→1 D→4* - This option incorrectly matches Niacin with Bitot's spots (Vitamin A deficiency) and Retinol with Dermatitis (Niacin deficiency). - The correct associations are Thiamine with cardiac failure, Niacin with dermatitis, Retinol with Bitot's spots, and Cholecalciferol with rachitic rosary. *A→1 B→4 C→2 D→3* - This option incorrectly matches Thiamine with dermatitis, Niacin with rachitic rosary, and Cholecalciferol with cardiac failure. - Each of these pairings contradicts the established clinical manifestations of the respective vitamin deficiencies. *A→4 B→2 C→1 D→3* - This option incorrectly associates Thiamine with rachitic rosary, Niacin with Bitot's spots, and Retinol with dermatitis. - The symptoms listed are characteristic of different vitamin deficiencies than those incorrectly matched in this choice. [Practice more Biochemistry PYQs on OnCourse]

Q: An average-sized hen egg would provide

70 Kcal. ***70 Kcal*** - An average-sized hen egg (approximately 50 grams) typically provides around **70-75 kilocalories** of energy. - This energy content is primarily derived from the egg's **protein and fat** components. *90 Kcal* - This value is slightly higher than the average for a standard hen egg and might be applicable to a **larger-sized egg** or if additional ingredients are included. - The precise caloric content varies with the **size and preparation** of the egg. *50 Kcal* - This value is generally **too low** for an average-sized whole hen egg. - An egg white alone might be closer to this caloric count, as **most of the fat and calories are in the yolk**. *110 Kcal* - This caloric value is significantly **higher** than what an average hen egg provides. - Such a high value would typically be found in **very large eggs** or in egg preparations that include added fats like butter or oil. [Practice more Biochemistry PYQs on OnCourse]

7 Previous Year Questions with Answers & Explanations

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Consider the following statements: 1. Diets high in vitamin C have been claimed to lower the incidence of certain cancers, particularly oesophageal and gastric cancers. 2. Vitamin C can prevent the conversion of nitrites and secondary amines to carcinogenic nitrosamines. Which of the statements given above is/are correct?

The biological value of a given protein depends upon

Which one of the following vitamins given as a supplement during the peri-conceptional period to a woman can help prevent the neural tube defects in the baby ?

Match List-I with List-II and select the correct answer using the code given below the Lists:

An average-sized hen egg would provide

Which one of the following is a polyunsaturated fatty acid ?

Which of the following dietary sources contains the lowest percent of linoleic acid?

UPSC-CMS 2012 - Biochemistry UPSC-CMS Practice Questions and MCQs

Question 1: Consider the following statements: 1. Diets high in vitamin C have been claimed to lower the incidence of certain cancers, particularly oesophageal and gastric cancers. 2. Vitamin C can prevent the conversion of nitrites and secondary amines to carcinogenic nitrosamines. Which of the statements given above is/are correct?

A. 1 only
B. 2 only
C. Both 1 and 2 (Correct Answer)
D. Neither 1 nor 2

Explanation: ***Both 1 and 2*** - **Statement 1 is correct:** Epidemiological studies have consistently shown that diets high in vitamin C are associated with a **lower incidence of oesophageal and gastric cancers**, attributed to its antioxidant properties and protective mechanisms. - **Statement 2 is correct:** Vitamin C acts as a **reducing agent that blocks nitrosamine formation** by preventing nitrites and secondary amines from reacting to form these carcinogenic compounds in the acidic gastric environment. - Both statements are **independently true and complementary** - statement 2 explains one of the key mechanisms by which statement 1's observation occurs. *1 only* - This option is incorrect because it ignores statement 2, which describes a **well-established biochemical mechanism** of vitamin C's cancer-protective effect. - The ability of vitamin C to prevent nitrosamine formation is a **proven protective mechanism**, not just a claim. *2 only* - This option is incorrect because it ignores statement 1, which accurately reflects **epidemiological evidence** linking high vitamin C intake with reduced cancer risk. - The association between dietary vitamin C and lower cancer incidence is **well-documented in observational studies**. *Neither 1 nor 2* - This option is completely incorrect as **both statements are scientifically accurate** and supported by substantial evidence. - Vitamin C's role in **cancer prevention through antioxidant activity and nitrosamine inhibition** is well-established in biochemistry and nutrition science.

Question 2: The biological value of a given protein depends upon

A. Digestibility and leucine content
B. Digestibility and amino acid composition (Correct Answer)
C. Amino acid composition and specific dynamic effect
D. Amino acid composition alone

Explanation: ***Digestibility and amino acid composition*** - The **biological value (BV)** of a protein measures how efficiently the body can use the absorbed protein from a food source for growth and maintenance. - It is primarily determined by two factors: the **digestibility** of the protein (how much is absorbed) and its **amino acid composition** (the proportion and availability of essential amino acids). *Digestibility and leucine content* - While **digestibility** is an important factor for biological value, **leucine content** alone is not sufficient to determine it. - The biological value depends on the **overall balance of essential amino acids**, not just one specific amino acid. *Amino acid composition and specific dynamic effect* - **Amino acid composition** is crucial for biological value, but the **specific dynamic effect (SDE)**, also known as the thermic effect of food, refers to the energy expended during the digestion, absorption, and assimilation of food. - SDE is related to energy metabolism, not directly to the protein's utility for tissue synthesis. *Amino acid composition alone* - **Amino acid composition** is a key determinant, particularly the presence and proportion of **essential amino acids**. - However, for a protein to be utilized, it must first be **digested and absorbed**, making digestibility an equally critical factor affecting its overall biological value.

Question 3: Which one of the following vitamins given as a supplement during the peri-conceptional period to a woman can help prevent the neural tube defects in the baby ?

A. Riboflavin
B. Folic acid (Correct Answer)
C. Thiamine
D. Vitamin B12

Explanation: ***Folic acid*** - **Folic acid** (vitamin B9) supplementation is crucial during the **peri-conceptional period** to prevent neural tube defects. - Adequate folic acid intake helps in the proper development and closure of the **neural tube** in the embryo, which forms the brain and spinal cord. *Riboflavin* - **Riboflavin** (vitamin B2) is essential for energy metabolism and cellular growth but has no direct, established role in preventing neural tube defects. - Deficiency can lead to **ariboflavinosis**, characterized by skin lesions, but not directly linked to neural tube malformations. *Thiamine* - **Thiamine** (vitamin B1) is vital for carbohydrate metabolism and nerve function. - Its deficiency causes **beriberi** and neurological problems in adults, but it does not directly prevent neural tube defects. *Vitamin B12* - **Vitamin B12** (cobalamin) is important for DNA synthesis and nerve function, and it works closely with folate. - While B12 deficiency can lead to megaloblastic anemia and neurological issues, **folic acid** is the primary vitamin for preventing neural tube defects.

Question 4: Match List-I with List-II and select the correct answer using the code given below the Lists:

A. A→3 B→2 C→1 D→4
B. A→1 B→4 C→2 D→3
C. A→4 B→2 C→1 D→3
D. A→3 B→1 C→2 D→4 (Correct Answer)

Explanation: ***A→3 B→1 C→2 D→4*** - **Thiamine (Vitamin B1)** deficiency can lead to **beriberi**, which often manifests as **wet beriberi** characterized by **high-output cardiac failure**, edema, and peripheral neuropathy. - **Niacin (Vitamin B3)** deficiency causes **pellagra**, a disease classically presenting with the "4 Ds": **dermatitis**, diarrhea, dementia, and death. - **Retinol (Vitamin A)** deficiency is primarily known for causing **xerophthalmia**, which includes early signs like **night blindness** and later stages like Bitot's spots (foamy keratin debris on the conjunctiva) and keratomalacia. - **Cholecalciferol (Vitamin D)** deficiency leads to **rickets in children**, characterized by impaired bone mineralization causing skeletal deformities such as a **rachitic rosary** (enlargement of the costochondral junctions). *A→3 B→2 C→1 D→4* - This option incorrectly matches Niacin with Bitot's spots (Vitamin A deficiency) and Retinol with Dermatitis (Niacin deficiency). - The correct associations are Thiamine with cardiac failure, Niacin with dermatitis, Retinol with Bitot's spots, and Cholecalciferol with rachitic rosary. *A→1 B→4 C→2 D→3* - This option incorrectly matches Thiamine with dermatitis, Niacin with rachitic rosary, and Cholecalciferol with cardiac failure. - Each of these pairings contradicts the established clinical manifestations of the respective vitamin deficiencies. *A→4 B→2 C→1 D→3* - This option incorrectly associates Thiamine with rachitic rosary, Niacin with Bitot's spots, and Retinol with dermatitis. - The symptoms listed are characteristic of different vitamin deficiencies than those incorrectly matched in this choice.

Question 5: An average-sized hen egg would provide

A. 90 Kcal
B. 70 Kcal (Correct Answer)
C. 50 Kcal
D. 110 Kcal

Explanation: ***70 Kcal*** - An average-sized hen egg (approximately 50 grams) typically provides around **70-75 kilocalories** of energy. - This energy content is primarily derived from the egg's **protein and fat** components. *90 Kcal* - This value is slightly higher than the average for a standard hen egg and might be applicable to a **larger-sized egg** or if additional ingredients are included. - The precise caloric content varies with the **size and preparation** of the egg. *50 Kcal* - This value is generally **too low** for an average-sized whole hen egg. - An egg white alone might be closer to this caloric count, as **most of the fat and calories are in the yolk**. *110 Kcal* - This caloric value is significantly **higher** than what an average hen egg provides. - Such a high value would typically be found in **very large eggs** or in egg preparations that include added fats like butter or oil.

Question 6: Which one of the following is a polyunsaturated fatty acid ?

A. Stearic acid
B. Oleic acid
C. Linoleic acid (Correct Answer)
D. Palmitic acid

Explanation: ***Linoleic acid*** - **Linoleic acid** contains **two double bonds** in its carbon chain making it a **polyunsaturated fatty acid (PUFA)**. - It is an **omega-6 fatty acid**, and an essential fatty acid, meaning it cannot be synthesized by the human body and must be obtained from the diet. *Stearic acid* - **Stearic acid** is a **saturated fatty acid** with no double bonds in its hydrocarbon chain. - Saturated fatty acids are typically solid at room temperature and primarily found in animal fats. *Oleic acid* - **Oleic acid** is a **monounsaturated fatty acid (MUFA)**, meaning it contains only **one double bond** in its carbon chain. - It is an **omega-9 fatty acid**, commonly found in olive oil. *Palmitic acid* - **Palmitic acid** is also a **saturated fatty acid**, similar to stearic acid, with no double bonds. - It is one of the most common saturated fatty acids in animals and plants and is a major component of palm oil.

Question 7: Which of the following dietary sources contains the lowest percent of linoleic acid?

A. Coconut oil (Correct Answer)
B. Corn oil
C. Mustard oil
D. Groundnut oil

Explanation: ***Coconut oil*** - Coconut oil is primarily composed of **saturated fats**, particularly **lauric acid**, and has a very low percentage of linoleic acid. - Its high saturated fat content distinguishes it from most other vegetable oils, which are generally rich in unsaturated fats. *Corn oil* - Corn oil is a **polyunsaturated fatty acid (PUFA)**-rich oil, with a significant proportion of **linoleic acid** (an omega-6 fatty acid). - It is often used in cooking for its neutral flavor and high smoke point. *Mustard oil* - Mustard oil contains a substantial amount of **monounsaturated fatty acids (MUFA)**, like **erucic acid**, and also a notable percentage of **linoleic acid**. - Its distinct pungent flavor is popular in certain cuisines. *Groundnut oil* - Groundnut oil, also known as peanut oil, is rich in both **monounsaturated** and **polyunsaturated fatty acids**, including a good percentage of **linoleic acid**. - It is commonly used for frying due to its high smoke point and mild flavor.