Which immunoglobulin is known to be heat-labile?
Which of the following is not an acute phase reactant?
All of the following are required more during lactation as compared to pregnancy, except ?
What is the iron requirement for a normal menstruating adult female?
Which of the following conditions is primarily treated with Vitamin B6?
3 beta hydroxysteroid dehydrogenase deficiency causes increased production of -
Which of the following statements about Maple Syrup Urine Disease (MSUD) is true?
What is the effect of moderate alcohol consumption on lipid profiles in dyslipidemia?
Cystatin C levels are used for
Critical temperature for liquid nitrogen is ?
NEET-PG 2013 - Biochemistry NEET-PG Practice Questions and MCQs
Question 121: Which immunoglobulin is known to be heat-labile?
- A. IgA
- B. IgG
- C. IgM (Correct Answer)
- D. IgE
Explanation: ***IgM*** - **IgM** is known for its **heat lability** and is readily denatured at 56°C within a few minutes. - This characteristic is due to its **pentameric structure** held together by disulfide bonds and J chains, which are sensitive to thermal denaturation. - Heat lability of IgM is clinically important in complement fixation tests and other laboratory assays where heat inactivation is performed. - IgM is the first antibody produced in primary immune response and its heat sensitivity distinguishes it from other immunoglobulins. *IgA* - **IgA** exists in monomeric (serum) and dimeric (secretory) forms and shows moderate stability to heat. - Secretory IgA is relatively stable as it needs to function in harsh mucosal environments, though not as heat-resistant as IgG. - Does not exhibit the pronounced heat lability characteristic of IgM. *IgG* - **IgG** is the most stable immunoglobulin and is highly resistant to heat denaturation. - Can withstand temperatures up to 60-70°C without significant loss of activity. - Its monomeric structure with strong intramolecular bonds provides exceptional thermal stability. - Most abundant antibody in serum and has the longest half-life. *IgE* - **IgE** is actually quite stable to heat and can withstand 56°C for extended periods. - While it has a short half-life in serum (2-3 days), this is due to receptor binding rather than heat instability. - Important in type I hypersensitivity reactions and parasitic infections. - Does not show the characteristic heat lability that defines IgM.
Question 122: Which of the following is not an acute phase reactant?
- A. C-reactive protein
- B. Haptoglobin
- C. Endothelin (Correct Answer)
- D. Fibrinogen
Explanation: ***Endothelin*** - Endothelin is a **vasoconstrictive peptide** primarily involved in regulating **blood vessel tone** and blood pressure. - While it plays a role in processes like inflammation and tissue repair, it is not synthesized or regulated in the same rapid, systemic manner as a classic acute phase reactant. *C-reactive protein* - **C-reactive protein (CRP)** is a rapidly responding acute phase reactant produced by the liver in response to **inflammation**, infection, and tissue injury. - Its levels can rise dramatically within hours of an inflammatory stimulus and are used as a marker for disease activity. *Haptoglobin* - **Haptoglobin** is an acute phase reactant that binds to free **hemoglobin** released from red blood cells during hemolysis, preventing oxidative damage. - Its levels typically increase during acute inflammation or infection, although it can also decrease with severe hemolysis. *Fibrinogen* - **Fibrinogen** is a critical acute phase protein involved in the **coagulation cascade** and wound healing. - Its concentration increases significantly during acute inflammation, contributing to the elevated **erythrocyte sedimentation rate (ESR)**.
Question 123: All of the following are required more during lactation as compared to pregnancy, except ?
- A. Niacin
- B. Energy
- C. Iron (Correct Answer)
- D. Vitamin A
Explanation: ***Iron*** - **Iron requirements are significantly higher during pregnancy** (~27 mg/day) due to the expansion of maternal red blood cell mass, fetal development, and placental iron needs. - During lactation, iron requirement decreases to **~9-10 mg/day**, lower than in pregnancy, as **lactational amenorrhea** (absence of menstruation) reduces iron loss. - This represents the **most significant decrease** in requirement from pregnancy to lactation among the listed nutrients. *Vitamin A* - The **recommended daily allowance (RDA) for Vitamin A is higher during lactation** (~1300 μg/day) compared to pregnancy (~800 μg/day). - This increased requirement ensures **adequate transfer to breast milk** to support infant's **vision development and immune function**. *Niacin* - **Niacin requirements during lactation** (~17 mg/day) are **similar to pregnancy** (~18 mg/day). - While lactation involves increased metabolic demands, niacin requirements do not show a marked increase compared to pregnancy, unlike Vitamin A and Energy. - This option is less clearly "required more" during lactation. *Energy* - **Energy requirements are significantly higher during lactation** to fuel milk production, which is energetically demanding. - A lactating woman typically needs an **additional 500 kcal/day**, compared to ~300 kcal/day in the 2nd/3rd trimester of pregnancy.
Question 124: What is the iron requirement for a normal menstruating adult female?
- A. 30 mg/day
- B. 35 mg/day
- C. 20 mg/day
- D. 15 mg/day (Correct Answer)
Explanation: ***15 mg/day*** - The recommended daily iron intake for a normal menstruating adult female was **15 mg/day** according to guidelines at the time of this examination (NEET-2013). - This higher requirement compared to males and post-menopausal women is due to **iron loss in menstrual blood**, averaging approximately **0.5-1 mg/day** additional iron loss. - **Note:** Current guidelines recommend **18 mg/day** (US RDA) or **21 mg/day** (ICMR, India), but this question reflects the 2013 standard. *20 mg/day* - This amount is **higher than the typical recommendation** for healthy menstruating women without significant pathology. - While some women with heavier menstrual bleeding might require this, it's not the baseline requirement for normal menstruation. *30 mg/day* - This intake level is typically recommended for **pregnant women** in the second and third trimesters or individuals with **diagnosed iron deficiency anemia** requiring therapeutic supplementation. - It is significantly more than the daily requirement for a healthy menstruating female. *35 mg/day* - This is an **excessively high** daily iron intake for a healthy menstruating female. - Such high doses are usually prescribed for **severe iron deficiency anemia** or specific medical conditions under supervision. - Chronic intake at this level without medical indication could potentially lead to adverse effects.
Question 125: Which of the following conditions is primarily treated with Vitamin B6?
- A. Cystathionuria
- B. None of the options
- C. Xanthourenic aciduria
- D. Homocystinuria (Correct Answer)
Explanation: ***Homocystinuria*** - The most common form of **homocystinuria** is caused by **cystathionine β-synthase (CBS) deficiency**, which requires **pyridoxal phosphate (Vitamin B6)** as a cofactor. - Approximately **50% of patients** with CBS deficiency are **B6-responsive**, making **high-dose Vitamin B6 (100-500 mg/day)** a **first-line primary treatment** for these cases. - This is a **clinically significant condition** that requires treatment, manifesting with features like **ectopia lentis, marfanoid habitus, intellectual disability, and thromboembolism**. - B6 supplementation enhances residual CBS enzyme activity and reduces plasma homocysteine levels. *Cystathionuria* - Caused by **cystathionine γ-lyase deficiency**, which also uses **Vitamin B6** as a cofactor. - This is generally a **benign, asymptomatic condition** that does **NOT require treatment**. - While B6 can reduce cystathionine accumulation, it is **not a primary treatment indication** because the condition is clinically insignificant. *Xanthurenic aciduria* - Caused by **kynureninase deficiency** in the **tryptophan metabolism pathway**, which requires **pyridoxal phosphate**. - This is a **rare and usually benign condition** that does not typically require treatment. - Not a primary indication for B6 therapy. *None of the options* - Incorrect, as **Homocystinuria** (CBS deficiency) is a **primary indication** for high-dose Vitamin B6 therapy in B6-responsive patients.
Question 126: 3 beta hydroxysteroid dehydrogenase deficiency causes increased production of -
- A. DHEA (Correct Answer)
- B. Progesterone
- C. Deoxycortisol
- D. Estradiol
Explanation: ***DHEA*** - The enzyme **3 beta-hydroxysteroid dehydrogenase (3β-HSD)** is crucial for converting **delta-5 steroids (pregnenolone, 17-OH-pregnenolone, and DHEA)** into **delta-4 steroids (progesterone, 17-OH-progesterone, and androstenedione)**. - A **deficiency** in 3β-HSD leads to the accumulation of its substrates, particularly **DHEA (dehydroepiandrosterone)** and **17-OH-pregnenolone**, due to the impaired conversion in the steroid synthesis pathway. - Among the accumulated substrates, **DHEA** has weak androgenic activity, making it clinically significant in this enzyme deficiency. *Progesterone* - **Progesterone** is a delta-4 steroid, which is synthesized from **pregnenolone** via the action of **3β-HSD**. - A deficiency in this enzyme would **decrease** the production of progesterone, not increase it, as the enzyme is required for its synthesis. *Deoxycortisol* - **Deoxycortisol (11-deoxycortisol)** is a precursor to cortisol, formed later in the adrenal steroid synthesis pathway from **17-hydroxyprogesterone**. - Its production would be **decreased** by a 3β-HSD deficiency, as the pathway is blocked upstream, reducing the formation of downstream products like cortisol and its precursors. *Estradiol* - **Estradiol** is an estrogen, synthesized from androgens (like testosterone) via the enzyme **aromatase**. - A deficiency in 3β-HSD would impair the production of androgens like androstenedione and testosterone, which are precursors for estradiol, thereby leading to a **decrease** in estradiol levels, not an increase.
Question 127: Which of the following statements about Maple Syrup Urine Disease (MSUD) is true?
- A. FeCl3 turns navy blue
- B. Asymptomatic
- C. Deficiency of branched chain amino acid enzymes (Correct Answer)
- D. Hyperaminoaciduria of aromatic amino acids
Explanation: ***Deficiency of branched chain amino acid enzymes*** - MSUD is caused by a deficiency in the **branched-chain alpha-keto acid dehydrogenase complex (BCKDC)**, an enzyme responsible for metabolizing **leucine, isoleucine, and valine**. - This enzyme deficiency leads to the accumulation of these **branched-chain amino acids (BCAAs)** and their corresponding branched-chain alpha-keto acids in the body. *Asymptomatic* - MSUD is a severe metabolic disorder that is **not asymptomatic**; it typically presents with distinct neurological and metabolic symptoms shortly after birth. - Clinical manifestations can include **poor feeding, lethargy, seizures**, and a characteristic **maple syrup odor** in urine and earwax. *FeCl3 turns navy blue* - The **ferric chloride test (FeCl3 test)** in MSUD typically yields a **green-gray or dark-green color** when testing for the accumulation of alpha-keto acids (specifically alpha-ketoisocaproic acid). - A **navy blue color** with FeCl3 is more characteristic of **alkaptonuria** due to the presence of homogentisic acid. *Hyperaminoaciduria of aromatic amino acids* - MSUD is characterized by the accumulation and excretion of **branched-chain amino acids (leucine, isoleucine, valine)** and their corresponding keto acids. - **Hyperaminoaciduria of aromatic amino acids** (e.g., phenylalanine, tyrosine, tryptophan) is seen in other conditions like **phenylketonuria (PKU)**, not MSUD.
Question 128: What is the effect of moderate alcohol consumption on lipid profiles in dyslipidemia?
- A. Decreased HDL levels
- B. Increased HDL levels (Correct Answer)
- C. Increased triglyceride levels
- D. Decreased LDL levels
Explanation: ***Increased HDL levels*** - Moderate alcohol consumption is known to **increase high-density lipoprotein (HDL) cholesterol levels**, which is often considered beneficial for cardiovascular health. - This effect is thought to be mediated by alcohol's influence on **hepatic lipoprotein metabolism**, leading to enhanced HDL production and reduced catabolism. *Decreased HDL levels* - This is incorrect, as multiple studies have consistently shown that **moderate alcohol consumption** tends to elevate, rather than decrease, HDL cholesterol. - Low HDL levels are associated with increased cardiovascular risk, making this effect an undesirable outcome that is not typical of moderate drinking. *Increased triglyceride levels* - While heavy or chronic alcohol consumption can lead to **increased triglyceride levels**, moderate intake typically has a neutral or only slightly elevated effect, if any, often overshadowed by the HDL increase. - Significant hypertriglyceridemia is a concern with **excessive alcohol use**, not usually with moderate consumption in healthy individuals. *Decreased LDL levels* - Moderate alcohol consumption generally has **little to no significant effect** on **low-density lipoprotein (LDL) cholesterol levels**, often referred to as "bad" cholesterol. - While HDL increases are observed, alcohol does not effectively lower LDL, which is a primary target in the management of dyslipidemia.
Question 129: Cystatin C levels are used for
- A. Detecting UTI
- B. Estimating GFR (Correct Answer)
- C. Screening for Renal Ca
- D. Estimating difference between CRF and ARF
Explanation: ***Estimating GFR*** - **Cystatin C** is a **proteinase inhibitor** produced by all nucleated cells at a constant rate, and its level in the blood is inversely related to the **glomerular filtration rate (GFR)**. - Unlike **creatinine**, Cystatin C levels are less affected by **muscle mass, diet, or inflammation**, making it a more reliable marker for early and subtle changes in GFR, especially in certain populations. *Detecting UTI* - **Urinary tract infections (UTIs)** are primarily detected through **urinalysis** (presence of **leukocytes, nitrites**, and **bacteria**) and **urine culture**. - **Cystatin C** is a serum marker for renal function and has no direct role in detecting the presence of bacterial infection in the urinary tract. *Estimating difference between CRF and ARF* - Differentiating between **chronic renal failure (CRF)** and **acute renal failure (ARF)** typically involves assessing the **chronicity of symptoms**, trend in **creatinine levels**, and **kidney size** and **echogenicity** on ultrasound. - While Cystatin C can reflect current GFR, it doesn't inherently provide discriminatory power between acute and chronic processes without serial measurements or additional clinical context. *Screening for Renal Ca* - **Renal cell carcinoma (RCC)** screening is primarily done using **imaging techniques** like **ultrasonography, CT, or MRI**, especially in individuals with risk factors or symptoms like **hematuria**. - **Cystatin C** is a marker of kidney function and does not serve as a tumor marker for renal cancer.
Question 130: Critical temperature for liquid nitrogen is ?
- A. 36.5°C
- B. -20°C
- C. -147°C (Correct Answer)
- D. -242°C
Explanation: ***-147°C*** - The **critical temperature** is the temperature above which a gas cannot be liquefied, no matter how much pressure is applied. For **liquid nitrogen**, this value is approximately **-147°C**. - At temperatures above **-147°C**, nitrogen exists only in its gaseous phase. *36.5°C* - This temperature is close to **human body temperature** and is not relevant to the critical temperature of nitrogen. - Nitrogen would be in a gaseous state at this temperature and below its critical pressure. *-20°C* - While a low temperature, **-20°C** is still well above nitrogen's **critical temperature**. - At **-20°C**, nitrogen would be a gas unless subjected to very high pressures. *-242°C* - This temperature is below the **critical temperature** of nitrogen, but it is also below its **boiling point** of **-196°C**. - At **-242°C**, nitrogen would be a liquid, but this value is not its critical temperature.