NEET-PG 2013 Practice Questions

Q: Which of the following statements about vitamin E is false?

Water soluble vitamin. ***Water soluble vitamin*** - This statement is false because **vitamin E** is a **fat-soluble vitamin**, meaning it dissolves in lipids and is stored in the body's fatty tissues and liver. - Its absorption requires the presence of dietary fat and bile salts, unlike water-soluble vitamins. *Act as antioxidant* - **Vitamin E** is a powerful **lipid-soluble antioxidant**, protecting cell membranes from damage by scavenging **free radicals**. - It helps prevent **oxidative damage** to polyunsaturated fatty acids within cell membranes. *Chemically tocopherol* - The most biologically active form of **vitamin E** is **alpha-tocopherol**, although vitamin E encompasses a group of eight fat-soluble compounds, including tocopherols and tocotrienols. - This term correctly identifies the chemical nature of the prominent forms of vitamin E. *Prevent lipid peroxidation of cell membrane* - As an **antioxidant**, **vitamin E** specifically interferes with the **propagation of lipid peroxidation**, a chain reaction that damages cell membranes by oxidizing their lipid components. - It donates an electron to **free radicals**, thereby neutralizing them and protecting the integrity of the cell membrane.

Q: Which of the following is a natural uncoupler found in brown adipose tissue?

Thermogenin. ***Correct: Thermogenin*** - Also known as **uncoupling protein 1 (UCP1)**, it is a **mitochondrial inner membrane protein** naturally expressed in **brown adipose tissue** - Thermogenin creates a **proton leak** across the inner mitochondrial membrane, bypassing ATP synthase and dissipating the proton gradient as heat, thereby mediating **non-shivering thermogenesis** - This is the only natural uncoupler among the options listed *Incorrect: 2,4-Nitrophenol* - This compound is **not a naturally occurring uncoupler** in mammalian tissues - While it can act as a synthetic uncoupler in laboratory settings, it is not found in biological systems *Incorrect: 2,4-Dinitrophenol* - This is a well-known **synthetic chemical uncoupler** of oxidative phosphorylation, historically used as a weight-loss drug (now banned due to toxicity) - It works by carrying protons across the inner mitochondrial membrane, but it is **not a natural biological molecule** found in the body *Incorrect: Oligomycin* - Oligomycin is an **inhibitor of ATP synthase (Complex V)**, not an uncoupler - It binds to the F0 subunit of ATP synthase, blocking the flow of protons through the enzyme and thereby preventing ATP synthesis - This blocks both the proton gradient dissipation AND ATP production, which is mechanistically different from uncoupling

Q: Fructose intolerance is due to deficiency of which enzyme?

Aldolase B. ***Aldolase B*** - **Hereditary fructose intolerance** is a genetic disorder caused by a deficiency in the enzyme **aldolase B**. - This deficiency leads to an accumulation of **fructose-1-phosphate** in the liver, kidneys, and small intestine, causing **hypoglycemia**, **vomiting**, and **liver damage** upon exposure to fructose. *Fructokinase* - A deficiency in **fructokinase** causes **essential fructosuria**, a benign metabolic disorder. - This condition is asymptomatic because **fructose** simply accumulates in the blood and urine without causing significant clinical problems. *Triokinase* - **Triokinase**, also known as **glycerol kinase**, is involved in glycerol metabolism, converting glycerol to **glycerol-3-phosphate**. - Its deficiency is not directly linked to fructose intolerance and typically presents with **hyperglycerolemia**. *Aldolase A* - **Aldolase A** is one of the three aldolase isoenzymes (A, B, and C) and is primarily involved in **glycolysis**, specifically in the breakdown of **fructose-1,6-bisphosphate**. - A deficiency in aldolase A can lead to **hemolytic anemia** and **myopathy**, not directly fructose intolerance.

Q: Which of the following statements about gluconeogenesis is correct?

Occurs mainly in the liver. ***Occurs mainly in the liver*** - The **liver** is the primary site for **gluconeogenesis**, responsible for maintaining blood glucose levels during fasting. - The kidneys also contribute, especially during prolonged fasting, but to a lesser extent. *It uses exactly the same enzymes as glycolysis in reverse* - While gluconeogenesis shares some enzymes with glycolysis, there are **three irreversible steps in glycolysis** that require different enzymes in gluconeogenesis to bypass them. - Key bypass enzymes include **pyruvate carboxylase**, **phosphoenolpyruvate carboxykinase (PEPCK)**, **fructose-1,6-bisphosphatase**, and **glucose-6-phosphatase**. *It only occurs during fed state when insulin levels are high* - **Gluconeogenesis is activated during fasting or starvation** when blood glucose levels are low, and it is largely **inhibited by high insulin levels**. - Its purpose is to produce new glucose to prevent hypoglycemia, not to store excess glucose. *Fatty acids are the primary substrate for gluconeogenesis* - **Fatty acids cannot be directly converted to glucose** in significant amounts in humans because they are broken down into acetyl-CoA, which cannot be used for net glucose synthesis. - Primary substrates include **lactate**, **amino acids** (from protein breakdown), and **glycerol** (from triglyceride breakdown).

Q: The main function of Vitamin C in the body is

Cofactor for hydroxylation reactions in collagen synthesis. ***Cofactor for hydroxylation reactions in collagen synthesis*** - Vitamin C (ascorbic acid) serves as an essential **cofactor** for **prolyl hydroxylase** and **lysyl hydroxylase** enzymes. - These enzymes catalyze the **hydroxylation of proline and lysine** residues in collagen, forming **hydroxyproline** and **hydroxylysine**. - This hydroxylation is crucial for the **stability and cross-linking** of collagen triple helix structure. - Deficiency leads to **scurvy**, characterized by defective collagen synthesis, bleeding gums, poor wound healing, and bone abnormalities. - This is the **primary and main function** of Vitamin C in the human body. *Involvement as antioxidant* - While Vitamin C does act as a **water-soluble antioxidant**, protecting cells from oxidative damage by free radicals, this is a **secondary function**. - It can donate electrons to neutralize reactive oxygen species and regenerate other antioxidants like Vitamin E. - This protective role is important but not the main function compared to its role in collagen synthesis. *Regulation of lipid synthesis* - Vitamin C is **not directly involved** in the primary pathways of lipid synthesis or metabolism. - It may play a minor role in **carnitine synthesis** (needed for fatty acid oxidation), but this is not a major function. - Other nutrients like B vitamins play more significant roles in lipid metabolism regulation. *Inhibition of cell growth* - Vitamin C does **not inhibit normal cell growth**; it is essential for cell health, differentiation, and tissue repair. - While high doses may have some anti-proliferative effects in certain cancer cell lines in vitro, this is not a physiological function in the healthy body.

Q: Curschmann's spirals are seen in which condition?

Bronchial asthma. ***Bronchial asthma*** - **Curschmann's spirals** are spiral-shaped mucus plugs found in the sputum of patients with **bronchial asthma**. - They represent casts from small bronchi and are formed from **mucus and cellular debris** within the airways during an asthmatic exacerbation. *Bronchiectasis* - Characterized by **permanent abnormal dilation** of the bronchi due to chronic inflammation and infection, leading to productive cough and recurrent respiratory infections. - While it involves mucous production, it is typically associated with **purulent sputum** due to bacterial colonization, not necessarily Curschmann's spirals. *Chronic bronchitis* - Defined clinically by a **chronic productive cough** for at least three months in each of two successive years, without other causes. - Involves mucus hypersecretion and inflammation, but **Curschmann's spirals are not a characteristic finding** compared to asthma. *Wegener's granulomatosis (Granulomatosis with Polyangiitis)* - This is a systemic **vasculitis** affecting small to medium-sized blood vessels, typically involving the upper and lower respiratory tracts and kidneys. - Its pulmonary manifestations include **nodules, cavities, and diffuse alveolar hemorrhage**, and sputum findings are related to inflammation and bleeding, not Curschmann's spirals.

Q: MALT lymphoma is positive for which of the following markers?

CD20. ***CD20*** - MALT lymphoma is a type of **B-cell non-Hodgkin lymphoma**, and CD20 is a **pan B-cell marker consistently expressed** in MALT lymphomas. - CD20 positivity is **crucial for diagnosis** and is the **primary therapeutic target** for anti-CD20 monoclonal antibody therapy (Rituximab). - In diagnostic practice, **CD20 is the most important B-cell marker** for identifying MALT lymphoma and guiding treatment decisions. *CD19* - CD19 is also a **pan B-cell marker** and is **typically positive in MALT lymphoma** along with CD20. - However, in the context of this question, **CD20 is the preferred answer** because it is the **standard diagnostic marker emphasized in clinical practice** and the **primary therapeutic target**. - Both markers are positive, but CD20 has greater **clinical and therapeutic significance** in MALT lymphoma management. *CD43* - CD43 is primarily a **T-cell and myeloid marker**, but can show **aberrant expression in 40-50% of MALT lymphomas**. - While it may be positive in some cases, it is **not a defining B-cell lineage marker** and is not used as a primary diagnostic criterion for MALT lymphoma. - Its variable expression makes it **less reliable** than consistent B-cell markers like CD20. *CD5* - CD5 is typically associated with **T-cells** and certain B-cell lymphomas, particularly **chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL)** and **mantle cell lymphoma**. - **MALT lymphoma is characteristically CD5-negative**, which is an important feature for **differentiating it from CD5+ B-cell lymphomas**.

Q: Which of the following is classified as an antispasmodic agent?

Dicyclomine. ***Dicyclomine*** - **Dicyclomine** is an **anticholinergic** medication that works by blocking muscarinic receptors, thereby reducing smooth muscle spasm in the gastrointestinal tract. - It is commonly used to treat symptoms of **irritable bowel syndrome (IBS)**, such as abdominal pain and cramping. *Physostigmine* - **Physostigmine** is a **cholinesterase inhibitor** that increases the concentration of acetylcholine at the synaptic cleft. - It is used to treat **anticholinergic poisoning** by reversing the effects of anticholinergic drugs, rather than acting as an antispasmodic itself. *Tropicamide* - **Tropicamide** is an **anticholinergic** agent primarily used as a **mydriatic** (pupil dilator) and **cycloplegic** (paralyzes the ciliary muscle) for ophthalmic examinations. - Its action is localized to the eye and it does not have significant systemic antispasmodic effects. *None of the options* - This option is incorrect because one of the listed medications is indeed classified as an antispasmodic agent. - When "None of the options" appears as a choice, it should only be selected if all other options are clearly incorrect.

Q: Ovulation occurs how long after the LH surge peak?

12-24 hours. ***12-24 hours*** - Ovulation, the release of a mature egg from the **ovary**, typically occurs within **12 to 24 hours after the peak of the luteinizing hormone (LH) surge**. - The LH surge itself usually lasts 24 to 48 hours and is a critical signal for the final maturation and release of the oocyte. *24-48 hours* - While the **LH surge** can last up to 48 hours, **ovulation** (the actual release of the egg) generally happens more rapidly, usually within 12-24 hours of the *peak* of this surge. - This timeframe is a common misconception, as it refers more to the duration of the surge rather than the precise timing of ovulation post-peak. *48-72 hours* - Ovulation rarely occurs this late after the peak of the **LH surge**; if it does, it suggests a potential delay or irregularity in the **ovulatory process**. - The window for successful fertilization is relatively narrow and aligns with the more immediate post-surge timing. *72-96 hours* - This time frame is significantly beyond the typical window for **ovulation** following the **LH surge**. - By this point, the egg would have either been released or the ovulatory event would have passed without the egg releasing.

Q: Which of the following is classified as a pain receptor?

Free nerve endings. ***Free nerve endings*** - **Free nerve endings** are the most common type of sensory receptor in the skin and are responsible for detecting **pain**, temperature, and crude touch. - They lack specialized structures and are found throughout the epidermis and dermis. *Meissner's corpuscle* - **Meissner's corpuscles** are encapsulated nerve endings that detect **light touch** and **vibration**. - They are rapidly adapting and are abundant in sensitive, hairless skin areas like fingertips and lips. *Pacinian corpuscle* - **Pacinian corpuscles** are large, encapsulated receptors that detect **deep pressure** and **vibration**. - They are rapidly adapting and respond to high-frequency stimuli. *Merkel disc* - **Merkel discs** are specialized epithelial cells associated with nerve endings that detect **sustained pressure** and **texture**. - They are slowly adapting receptors crucial for tactile discrimination.

Question 1

Which of the following statements about vitamin E is false?

Accepted Answer

Water soluble vitamin

Answer

Act as antioxidant

Answer

Chemically tocopherol

Answer

Prevent lipid peroxidation of cell membrane

Question 2

Which of the following is a natural uncoupler found in brown adipose tissue?

Accepted Answer

Thermogenin

Answer

2,4-Nitrophenol

Answer

2,4-Dinitrophenol

Answer

Oligomycin

Question 3

Fructose intolerance is due to deficiency of which enzyme?

Accepted Answer

Aldolase B

Answer

Aldolase A

Answer

Fructokinase

Answer

Triokinase

Question 4

Which of the following statements about gluconeogenesis is correct?

Accepted Answer

Occurs mainly in the liver

Answer

It uses exactly the same enzymes as glycolysis in reverse

Answer

It only occurs during fed state when insulin levels are high

Answer

Fatty acids are the primary substrate for gluconeogenesis

Question 5

The main function of Vitamin C in the body is

Accepted Answer

Cofactor for hydroxylation reactions in collagen synthesis

Answer

Regulation of lipid synthesis

Answer

Involvement as antioxidant

Answer

Inhibition of cell growth

Question 6

Curschmann's spirals are seen in which condition?

Accepted Answer

Bronchial asthma

Answer

Bronchiectasis

Answer

Chronic bronchitis

Answer

Wegener's granulomatosis

Question 7

MALT lymphoma is positive for which of the following markers?

Accepted Answer

CD20

Answer

CD19

Answer

CD43

Answer

CD5

Question 8

Which of the following is classified as an antispasmodic agent?

Accepted Answer

Dicyclomine

Answer

Physostigmine

Answer

Tropicamide

Answer

None of the options

Question 9

Ovulation occurs how long after the LH surge peak?

Accepted Answer

12-24 hours

Answer

48-72 hours

Answer

72-96 hours

Answer

24-48 hours

Question 10

Which of the following is classified as a pain receptor?

Accepted Answer

Free nerve endings

Answer

Meissner's corpuscle

Answer

Pacinian corpuscle

Answer

Merkel disc

NEET-PG 2013

Biochemistry

Pathology

Pharmacology

Physiology