UPSC-CMS 2023 — Biochemistry

Q: Which one of the following statements about Human Immunoglobulins is not correct?

IgG and IgM can both cross the placenta. ***IgG and IgM can both cross the placenta*** - This statement is incorrect because only **IgG** can actively cross the placenta, providing **passive immunity** to the fetus. - **IgM** is too large to cross the placental barrier, so its presence in a newborn suggests **congenital infection**. *The half life of IgM is about 10 days* - The approximate **half-life of IgM** is indeed around **5-10 days**, making this statement largely correct in general contexts. - This relatively short half-life means that IgM levels can change quickly in response to acute infections. *IgG comprises about 75-80% of the total serum immunoglobulins* - **IgG** is the most abundant immunoglobulin in serum, typically accounting for **75-80%** of the total immunoglobulins. - Its high concentration and long half-life contribute to its critical role in **secondary immune responses** and **long-term immunity**. *IgA comprises 15% of the total serum immunoglobulins and is mainly found in the body secretions* - **IgA** accounts for about **10-15%** of the total serum immunoglobulins, with a significant proportion found in secretions. - It plays a crucial role in **mucosal immunity**, protecting surfaces like the gastrointestinal, respiratory, and genitourinary tracts. [Practice more Biochemistry PYQs on OnCourse]

Q: Which food proteins among the following are considered to be the best and are used in nutritional studies as 'reference protein' ?

Egg proteins. ***Egg proteins*** - **Egg proteins** provide all **essential amino acids** in proportions that closely match human requirements, making them a **high-quality protein**. - Due to their excellent amino acid profile and high digestibility, **egg proteins** are often used as a **reference protein** in nutritional studies to evaluate the biological value of other proteins. *Milk proteins* - While **milk proteins** (casein and whey) are generally considered high-quality, their amino acid profile is not as perfectly balanced for human needs as egg protein. - They are commonly used as a reference for assessing protein quality, but **egg protein** often serves as the gold standard for comparison. *Legume proteins* - **Legume proteins** are typically deficient in **methionine and cysteine**, essential amino acids, making them an incomplete protein when consumed alone. - Their overall **biological value** is lower than animal proteins, and they are not considered a reference protein. *Wheat proteins* - **Wheat proteins** (gluten) are deficient in the **essential amino acid lysine**. - They have a lower **biological value** and are not as easily digestible as animal proteins, thus not suitable as a reference protein. [Practice more Biochemistry PYQs on OnCourse]

Q: Consider the following statements with reference to 'trans fatty acids' : 1. They are geometrical isomers of cis-unsaturated fatty acids. 2. Though atherogenic, being unsaturated they are less so than saturated fatty acids. 3. It takes years for trans fatty acids to be flushed from the body. 4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?

1 only. ***1 only*** - **Statement 1 is CORRECT**: Trans fatty acids are **geometrical isomers of cis-unsaturated fatty acids**, differing in the spatial arrangement of hydrogen atoms around the carbon-carbon double bond. This structural difference gives them physical and biological properties more similar to saturated fats. - **Statement 2 is INCORRECT**: Trans fatty acids are **MORE atherogenic** than saturated fatty acids, not less. They raise LDL cholesterol and lower HDL cholesterol more significantly than saturated fats. - **Statement 3 is INCORRECT**: Trans fatty acids are metabolized and eliminated from the body within **days to weeks**, not years. Long-term cardiovascular damage results from chronic dietary exposure, not slow elimination kinetics. - **Statement 4 is INCORRECT**: Trans fatty acids **raise LDL cholesterol** ("bad" cholesterol) and **lower HDL cholesterol** ("good" cholesterol). They do not lower both as stated. *1 and 3 only* - Statement 1 is correct, but statement 3 is **incorrect**. The body processes and eliminates trans fatty acids relatively quickly (days to weeks), not years. The detrimental cardiovascular effects accumulate due to chronic dietary exposure, not slow metabolism of individual molecules. *2, 3 and 4* - All three statements are **incorrect**. Statement 2 is wrong because trans fats are **more atherogenic** than saturated fats. Statement 3 is wrong because trans fats are metabolized within weeks, not years. Statement 4 is wrong because trans fats **raise LDL** (not lower it) while lowering HDL. *1, 3 and 4* - Only statement 1 is correct. Statement 3 is **incorrect** as trans fatty acids are metabolized within weeks, not years. Statement 4 is **incorrect** because trans fatty acids **increase LDL cholesterol** and **decrease HDL cholesterol** - they do not lower both. [Practice more Biochemistry PYQs on OnCourse]

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Which one of the following statements about Human Immunoglobulins is not correct?

Which food proteins among the following are considered to be the best and are used in nutritional studies as 'reference protein' ?

Consider the following statements with reference to 'trans fatty acids' : 1. They are geometrical isomers of cis-unsaturated fatty acids. 2. Though atherogenic, being unsaturated they are less so than saturated fatty acids. 3. It takes years for trans fatty acids to be flushed from the body. 4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?

UPSC-CMS 2023 - Biochemistry UPSC-CMS Practice Questions and MCQs

Question 1: Which one of the following statements about Human Immunoglobulins is not correct?

A. The half life of IgM is about 10 days
B. IgG comprises about 75-80% of the total serum immunoglobulins
C. IgA comprises 15% of the total serum immunoglobulins and is mainly found in the body secretions
D. IgG and IgM can both cross the placenta (Correct Answer)

Explanation: ***IgG and IgM can both cross the placenta*** - This statement is incorrect because only **IgG** can actively cross the placenta, providing **passive immunity** to the fetus. - **IgM** is too large to cross the placental barrier, so its presence in a newborn suggests **congenital infection**. *The half life of IgM is about 10 days* - The approximate **half-life of IgM** is indeed around **5-10 days**, making this statement largely correct in general contexts. - This relatively short half-life means that IgM levels can change quickly in response to acute infections. *IgG comprises about 75-80% of the total serum immunoglobulins* - **IgG** is the most abundant immunoglobulin in serum, typically accounting for **75-80%** of the total immunoglobulins. - Its high concentration and long half-life contribute to its critical role in **secondary immune responses** and **long-term immunity**. *IgA comprises 15% of the total serum immunoglobulins and is mainly found in the body secretions* - **IgA** accounts for about **10-15%** of the total serum immunoglobulins, with a significant proportion found in secretions. - It plays a crucial role in **mucosal immunity**, protecting surfaces like the gastrointestinal, respiratory, and genitourinary tracts.

Question 2: Which food proteins among the following are considered to be the best and are used in nutritional studies as 'reference protein' ?

A. Milk proteins
B. Legume proteins
C. Wheat proteins
D. Egg proteins (Correct Answer)

Explanation: ***Egg proteins*** - **Egg proteins** provide all **essential amino acids** in proportions that closely match human requirements, making them a **high-quality protein**. - Due to their excellent amino acid profile and high digestibility, **egg proteins** are often used as a **reference protein** in nutritional studies to evaluate the biological value of other proteins. *Milk proteins* - While **milk proteins** (casein and whey) are generally considered high-quality, their amino acid profile is not as perfectly balanced for human needs as egg protein. - They are commonly used as a reference for assessing protein quality, but **egg protein** often serves as the gold standard for comparison. *Legume proteins* - **Legume proteins** are typically deficient in **methionine and cysteine**, essential amino acids, making them an incomplete protein when consumed alone. - Their overall **biological value** is lower than animal proteins, and they are not considered a reference protein. *Wheat proteins* - **Wheat proteins** (gluten) are deficient in the **essential amino acid lysine**. - They have a lower **biological value** and are not as easily digestible as animal proteins, thus not suitable as a reference protein.

Question 3: Consider the following statements with reference to 'trans fatty acids' : 1. They are geometrical isomers of cis-unsaturated fatty acids. 2. Though atherogenic, being unsaturated they are less so than saturated fatty acids. 3. It takes years for trans fatty acids to be flushed from the body. 4. They lower both LDL cholesterol and HDL cholesterol in the body. Which of the statements given above are correct ?

A. 1 and 3 only
B. 2, 3 and 4
C. 1 only (Correct Answer)
D. 1, 3 and 4

Explanation: ***1 only*** - **Statement 1 is CORRECT**: Trans fatty acids are **geometrical isomers of cis-unsaturated fatty acids**, differing in the spatial arrangement of hydrogen atoms around the carbon-carbon double bond. This structural difference gives them physical and biological properties more similar to saturated fats. - **Statement 2 is INCORRECT**: Trans fatty acids are **MORE atherogenic** than saturated fatty acids, not less. They raise LDL cholesterol and lower HDL cholesterol more significantly than saturated fats. - **Statement 3 is INCORRECT**: Trans fatty acids are metabolized and eliminated from the body within **days to weeks**, not years. Long-term cardiovascular damage results from chronic dietary exposure, not slow elimination kinetics. - **Statement 4 is INCORRECT**: Trans fatty acids **raise LDL cholesterol** ("bad" cholesterol) and **lower HDL cholesterol** ("good" cholesterol). They do not lower both as stated. *1 and 3 only* - Statement 1 is correct, but statement 3 is **incorrect**. The body processes and eliminates trans fatty acids relatively quickly (days to weeks), not years. The detrimental cardiovascular effects accumulate due to chronic dietary exposure, not slow metabolism of individual molecules. *2, 3 and 4* - All three statements are **incorrect**. Statement 2 is wrong because trans fats are **more atherogenic** than saturated fats. Statement 3 is wrong because trans fats are metabolized within weeks, not years. Statement 4 is wrong because trans fats **raise LDL** (not lower it) while lowering HDL. *1, 3 and 4* - Only statement 1 is correct. Statement 3 is **incorrect** as trans fatty acids are metabolized within weeks, not years. Statement 4 is **incorrect** because trans fatty acids **increase LDL cholesterol** and **decrease HDL cholesterol** - they do not lower both.