NEET-PG 2012 Practice Questions

Q: Which of the following enzymes does not catalyze a reaction that directly produces ATP via substrate-level phosphorylation?

Hexokinase. ***Correct: Hexokinase*** **Hexokinase** catalyzes the transfer of a phosphate group from **ATP to glucose**, producing **glucose-6-phosphate** and ADP. This step **consumes ATP** rather than producing it via substrate-level phosphorylation. **Substrate-level phosphorylation** directly synthesizes ATP from ADP by transferring a high-energy phosphate group from a phosphorylated substrate; hexokinase performs the **opposite reaction** (ATP consumption). *Incorrect: Pyruvate kinase* **Pyruvate kinase** catalyzes the transfer of a phosphate group from **phosphoenolpyruvate (PEP)** to ADP, forming **pyruvate** and ATP. This is a classic example of **substrate-level phosphorylation** in glycolysis, directly generating ATP. *Incorrect: Succinate thiokinase* **Succinate thiokinase** (also known as succinyl-CoA synthetase) catalyzes the conversion of **succinyl-CoA to succinate**, simultaneously forming **GTP** (or ATP in some organisms) from GDP (or ADP) and inorganic phosphate. The GTP produced can be converted to ATP through nucleoside diphosphate kinase, representing substrate-level phosphorylation in the TCA cycle. *Incorrect: Phosphoglycerate kinase* **Phosphoglycerate kinase** catalyzes the transfer of a phosphate group from **1,3-bisphosphoglycerate** to ADP, yielding **3-phosphoglycerate** and ATP. This is a key enzymatic step in glycolysis that directly produces ATP through **substrate-level phosphorylation**.

Q: What is the simplest and most commonly used measure of mortality?

Crude death rate. ***Crude death rate*** - This is the simplest and most commonly used measure because it reflects the **total number of deaths** in a population over a specified period, relative to the mid-period population. - Its calculation requires only the total number of deaths and the total population size, making it easily accessible and widely applicable for **general mortality comparisons**. *Case fatality rate* - This measures the **proportion of individuals diagnosed with a specific disease** who die from that disease, rather than overall mortality in a population. - It is often used to assess the **severity of a disease** and is not a general measure of mortality. *Proportional mortality rate* - This indicates the **proportion of all deaths due to a specific cause** or age group, rather than the overall death rate in the population. - It does not represent the absolute risk of dying and is influenced by the prevalence of other causes of death. *Specific death rate* - This measure calculates the death rate for a **particular subgroup** (e.g., age-specific, cause-specific, or sex-specific), making it more detailed but not the simplest or most commonly used overall measure. - While more precise for specific analyses, it requires more granular data than the crude death rate.

Q: Calcium requirement above the normal during the first six months of lactation is -

600 mg/day. ***600 mg/day*** - The increased calcium requirement during the first six months of lactation is primarily due to the significant amount of calcium secreted in **breast milk** for infant bone development. - During lactation, approximately **210-300 mg of calcium per day** is lost through breast milk, and considering **absorption efficiency** and maintaining maternal **bone density**, an additional **600 mg/day** above baseline requirements is recommended. - This additional intake helps meet the demands of milk production and prevent maternal bone demineralization during the period of **peak lactation**. *400 mg/day* - While calcium needs are elevated in lactation, an additional **400 mg/day** is insufficient to fully compensate for the calcium loss through breast milk during the initial, high-volume milk production phase. - This amount does not adequately account for both milk calcium content and the need to maintain maternal bone health during the first six months of lactation. *550 mg/day* - This increment is close but is generally considered slightly below the recommended additional intake for optimal maternal health and infant nutrition during **peak lactation**. - Adequate calcium intake is crucial as insufficient levels can lead to a negative calcium balance and increased risk of maternal **osteoporosis**. *75 mg/day* - An additional **75 mg/day** is a negligible increase and is far too low to meet the substantial calcium demands during the first six months of lactation. - This amount would be grossly inadequate considering that lactating mothers lose approximately **210-300 mg of calcium per day** into breast milk alone, not accounting for maternal physiological needs.

Q: Which toxin is primarily responsible for epidemic dropsy?

Sanguinarine (from bloodroot). ***Sanguinarine (from bloodroot)*** - **Sanguinarine** is an alkaloid found in *Argemone mexicana* (Mexican prickly poppy/bloodroot) seeds - Epidemic dropsy occurs when **argemone oil contaminates cooking oils** (especially mustard oil) - Causes **bilateral pitting edema**, **congestive cardiac failure**, **respiratory distress**, and **glaucoma** - Toxin damages **capillary permeability**, leading to fluid leakage and widespread edema - Major outbreaks documented in India, particularly in **Bengal (1998)** and **Delhi (1998)** *BOAA* - **BOAA** (β-N-Oxalylamino-L-alanine) is found in *Lathyrus sativus* (grass pea/khesari dal) - Causes **neurolathyrism**, characterized by **spastic paraplegia** (irreversible lower limb paralysis) - Affects the **motor neurons**, not vascular permeability - Clinically distinct from epidemic dropsy with **no edema or cardiac involvement** *Aflatoxin B1* - Produced by *Aspergillus flavus* and *Aspergillus parasiticus* fungi - Potent **hepatotoxin** and **hepatocarcinogen** - Causes **acute liver necrosis** and **hepatocellular carcinoma** - Not associated with edema or epidemic dropsy *Pyrrolizidine alkaloids* - Found in plants like *Heliotropium* and *Crotalaria* species - Cause **hepatic veno-occlusive disease** (sinusoidal obstruction syndrome) - Present with **hepatomegaly**, **ascites**, and **jaundice** - Liver pathology, not the widespread peripheral edema seen in epidemic dropsy

Q: From which strain of virus is the rabies vaccine prepared?

Fixed Virus. ***Fixed Virus*** - The rabies vaccine is prepared from **fixed virus strains**, which are **attenuated** forms of the rabies virus that have lost their pathogenicity for humans through serial passages in animals or cell cultures. - This attenuation allows the virus to induce an immune response without causing disease, making it safe and effective for vaccination. - Examples include **Pitman-Moore strain**, **Flury strain (HEP/LEP)**, and **SAD strain**. *Street virus* - The **street virus** is the term used for the **wild-type rabies virus** as it occurs naturally in infected animals and causes clinical rabies disease. - Due to its high pathogenicity and ability to cause lethal infection, the street virus is **not used** for vaccine production. *Wild virus* - **Wild virus** is another term referring to the naturally occurring, **virulent rabies virus** found in infected animals. - Like the street virus, it is too pathogenic to be used directly in vaccine preparation. *Pasteur virus* - While **Louis Pasteur** pioneered rabies vaccination, "Pasteur virus" is not a standard terminology for vaccine strains. - The term **"fixed virus"** specifically denotes laboratory-adapted, attenuated strains regardless of their origin.

Q: Which of the following organisms can penetrate a normal intact cornea?

Gonococcus. ***Gonococcus*** - *Neisseria gonorrhoeae* is unique among bacteria in its ability to directly penetrate the **intact corneal epithelium**. - This characteristic makes it a highly virulent cause of **rapidly progressive corneal ulceration** and endophthalmitis, especially in neonates born to infected mothers. *Staphylococcus aureus* - *Staphylococcus aureus* typically requires some form of **corneal epithelial defect** (e.g., abrasion, foreign body) to invade and cause keratitis. - While it is a common cause of bacterial keratitis, it does not penetrate an **undamaged cornea**. *Streptococcus pneumoniae* - Similar to *S. aureus*, *Streptococcus pneumoniae* usually needs a **breach in the corneal epithelium** to establish an infection. - It is a frequent cause of **bacterial conjunctivitis** and keratitis but is not known for invading an intact cornea. *Listeria monocytogenes* - *Listeria monocytogenes* is an important human pathogen but is primarily known for causing **meningitis, sepsis, and perinatal infections**. - It is not a common cause of bacterial keratitis, and there is no evidence to suggest it can penetrate an **intact corneal surface**.

Q: One of the common fractures that occur during boxing by hitting with a closed fist is:

Bennett's fracture dislocation. ***Bennett's fracture dislocation*** - This is an **intra-articular fracture** of the base of the **first metacarpal**, extending into the carpometacarpal (CMC) joint. - It is frequently caused by axial compression with the thumb in a flexed and adducted position, a common injury mechanism in **punching a hard object** during boxing. *Monteggia fracture dislocation* - This injury involves a fracture of the **proximal ulna** coupled with an **anterior dislocation of the radial head**. - It is typically caused by a direct blow to the forearm or a fall on an outstretched hand with a hyperpronated forearm, not a direct punch. *Galeazzi fracture dislocation* - This involves a fracture of the **distal radius** with an associated **dislocation of the distal radioulnar joint (DRUJ)**. - It results from a fall on an outstretched hand with a hyperpronated forearm, which is not consistent with a boxing injury. *Smith's fracture* - Also known as a **reverse Colles' fracture**, this is a fracture of the **distal radius** with **volar displacement of the distal fragment**. - It typically results from a fall on a flexed wrist or a direct blow to the back of the wrist, not a punching injury.

Q: Thorium-induced tumor is which of the following?

Angiosarcoma of liver. ***Angiosarcoma of liver*** - Thorium exposure is specifically linked to the development of **angiosarcoma of the liver**, often seen in individuals with a history of thorium dioxide injection [1]. - This type of tumor arises from **vascular endothelial cells** and is highly aggressive, often leading to significant morbidity. *Lymphoma* - Lymphoma is associated with **immune system factors** and typically arises from lymphoid tissues, which do not correlate with thorium exposure. - **Hematological malignancies** such as lymphoma do not have a documented direct association with thorium as a causative agent. *Astrocytoma* - Astrocytomas originate from **glial cells** in the brain and are primarily influenced by genetic predispositions rather than environmental carcinogens like thorium. - There is no established relationship between **thorium exposure** and the incidence of brain tumors such as astrocytomas. *Renal cell carcinoma* - Renal cell carcinoma is commonly linked to **smoking, obesity**, and genetic factors rather than thorium exposure. - It does not have a recognized connection to thorium, which is more specifically associated with liver tumors. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 216-217.

Q: What is considered a toxic serum level of lithium?

2.6. **2.6 mEq/L** - **Lithium toxicity** is generally considered to occur when serum lithium levels are above **1.5 mEq/L** with severe toxicity typically seen at levels above **2.5 mEq/L**. - At a level of **2.6 mEq/L**, patients are at high risk for significant neurological symptoms such as seizures, coma, and even death. *0.6 mEq/L* - A serum lithium level of **0.6 mEq/L** is within the normal therapeutic range, which is typically between **0.6 and 1.2 mEq/L**. - At this concentration, lithium is generally effective for bipolar disorder and other conditions with minimal risk of toxicity. *12 mEq/L* - A serum lithium level of **12 mEq/L** would represent an **extremely severe and likely fatal level of toxicity**, far beyond typical therapeutic or even severely toxic ranges. - Survival at such a high concentration would be highly improbable, as it would cause irreversible organ damage and profound central nervous system depression. *<0.6 mEq/L* - A serum lithium level of **less than 0.6 mEq/L** is considered subtherapeutic, meaning it is unlikely to be effective in treating bipolar disorder or other conditions. - While not toxic, such a low level would indicate a lack of therapeutic benefit and potential for symptom recurrence.

Q: What is the mechanism of action of Clopidogrel?

Inhibition of ADP-mediated platelet activation. ***Inhibition of ADP-mediated platelet activation*** - Clopidogrel is an **antiplatelet agent** that works by a direct antagonistic action at the **P2Y12 receptor** on the surface of platelets. - This binding prevents adenosine diphosphate (ADP) from binding to its receptor, thereby inhibiting the activation of the **GP IIb/IIIa receptor complex** and subsequent platelet aggregation. *Inhibition of Thromboxane A2* - This mechanism of action is characteristic of **aspirin**, which inhibits the enzyme **cyclooxygenase-1 (COX-1)**. - COX-1 inhibition leads to reduced production of **Thromboxane A2**, a potent platelet aggregator and vasoconstrictor. *Inhibition of GP IIb/IIIa receptors* - While Clopidogrel ultimately affects the activation of **GP IIb/IIIa receptors**, it does not directly inhibit them. - Drugs like **abciximab**, **eptifibatide**, and **tirofiban** are direct inhibitors of the GP IIb/IIIa receptors, preventing fibrinogen binding and platelet aggregation. *No effect on platelet activation* - This statement is incorrect as Clopidogrel is a well-established **antiplatelet drug**. - Its therapeutic effect is specifically to **reduce platelet activation** and aggregation, thus preventing thrombotic events.

Question 1

Which of the following enzymes does not catalyze a reaction that directly produces ATP via substrate-level phosphorylation?

Accepted Answer

Hexokinase

Answer

Pyruvate kinase

Answer

Succinate thiokinase

Answer

Phosphoglycerate kinase

Question 2

What is the simplest and most commonly used measure of mortality?

Accepted Answer

Crude death rate

Answer

Case fatality rate

Answer

Specific death rate

Answer

Proportional mortality rate

Question 3

Calcium requirement above the normal during the first six months of lactation is -

Accepted Answer

600 mg/day

Answer

75 mg/day

Answer

400 mg/day

Answer

550 mg/day

Question 4

Which toxin is primarily responsible for epidemic dropsy?

Accepted Answer

Sanguinarine (from bloodroot)

Answer

BOAA

Answer

Aflatoxin B1

Answer

Pyrrolizidine alkaloids

Question 5

From which strain of virus is the rabies vaccine prepared?

Accepted Answer

Fixed Virus

Answer

Street virus

Answer

Wild virus

Answer

Pasteur virus

Question 6

Which of the following organisms can penetrate a normal intact cornea?

Accepted Answer

Gonococcus

Answer

Staphylococcus aureus

Answer

Streptococcus pneumoniae

Answer

Listeria monocytogenes

Question 7

One of the common fractures that occur during boxing by hitting with a closed fist is:

Accepted Answer

Bennett's fracture dislocation

Answer

Monteggia fracture dislocation

Answer

Galeazzi fracture dislocation

Answer

Smith's fracture

Question 8

Thorium-induced tumor is which of the following?

Accepted Answer

Angiosarcoma of liver

Answer

Lymphoma

Answer

Renal cell carcinoma

Answer

Astrocytoma

Question 9

What is considered a toxic serum level of lithium?

Accepted Answer

2.6

Answer

0.6

Answer

12

Answer

<0.6

Question 10

What is the mechanism of action of Clopidogrel?

Accepted Answer

Inhibition of ADP-mediated platelet activation

Answer

Inhibition of Thromboxane A2

Answer

Inhibition of GP IIb/IIIa receptors

Answer

No effect on platelet activation

NEET-PG 2012

Biochemistry

Community Medicine

Microbiology

Ophthalmology

Orthopaedics

Pathology

Pharmacology