NEET-PG 2012 Practice Questions

Q: What is the classification of the Y chromosome?

Submetacentric. ***Submetacentric*** - The **Y chromosome** is classified as submetacentric because its **centromere** is located off-center, resulting in two arms of unequal length. - The short arm (Yp) is smaller than the long arm (Yq), but not as disproportionate as in acrocentric chromosomes. - The **X chromosome** is also submetacentric, making both sex chromosomes belong to this category. *Metacentric* - A **metacentric chromosome** has its **centromere** located in the middle, resulting in two arms of approximately equal length. - Examples include chromosomes 1, 3, 16, 19, and 20, which have nearly equal arm ratios unlike the Y chromosome. *Acrocentric* - An **acrocentric chromosome** has its **centromere** located very close to one end, creating one very short arm and one very long arm. - The five acrocentric human chromosomes are **13, 14, 15, 21, and 22**, which possess satellite DNA and nucleolar organizing regions (NORs) on their short arms. - The **Y chromosome is NOT acrocentric** despite historical confusion; it has a more centrally positioned centromere than true acrocentric chromosomes. *None of the options* - This option is incorrect because the Y chromosome has a specific and well-established classification as **submetacentric** based on its centromere position and arm ratio.

Q: Which bone has the maximum anatomical contribution to the floor of the orbit?

Maxillary. ***Maxillary*** - The **maxilla** contributes the most significantly to the **orbital floor**, forming approximately **75%** of its surface area. - The orbital plate of the maxilla is a thin, triangular bone that also forms the roof of the **maxillary sinus**. *Zygomatic* - The **zygomatic bone** forms the **lateral wall** and the **lateral portion** of the **orbital floor**. - Its contribution to the overall floor is less extensive than that of the maxilla (approximately 20-25%). *Sphenoid* - The **sphenoid bone** does **NOT** contribute to the **orbital floor** at all. - It forms parts of the **posterior wall** and **lateral wall** (via greater and lesser wings) of the orbit, but has no anatomical contribution to the floor. *Palatine* - The **palatine bone** (via its orbital process) contributes a very small, **posterior-most part** of the **orbital floor**. - Its contribution is minimal (less than 5%) compared to the maxilla and zygomatic bone.

Q: Waldeyer's fascia lies?

Behind the rectum.. ***Behind the rectum*** - **Waldeyer’s fascia**, also known as the **sacrorectal fascia**, is a retrorectal connective tissue sheet located between the **rectum** and the **sacrum**. - It plays a crucial role in supporting the rectum and forms part of the posterior rectosacral space, separating the rectum from the sacral bone and nerves. *In front of the bladder* - The space in front of the bladder is typically referred to as the **retropubic space of Retzius**, containing loose connective tissue and fat. - No specific fascial layer named Waldeyer's fascia is located in this anterior position relative to the bladder. *Between the bladder and uterus* - This space, known as the **vesicouterine pouch** or **anterior cul-de-sac**, is a peritoneal reflection between the bladder and the uterus [1]. - It does not contain a structure known as Waldeyer's fascia. *Between the uterus and rectum* - This space is the **rectouterine pouch** or **Pouch of Douglas**, which is the deepest part of the peritoneal cavity in females [2]. - While important surgically, it does not correspond to the location of Waldeyer's fascia.

Q: The cofactor vitamin B12 is required for the following conversion:

Methyl malonyl CoA to succinyl CoA. ***Methyl malonyl CoA to succinyl CoA*** - **Vitamin B12**, in its active form **adenosylcobalamin**, is a crucial cofactor for the enzyme **methylmalonyl-CoA mutase**, which catalyzes the isomerization of **methylmalonyl-CoA to succinyl-CoA**. - This conversion is vital for the metabolism of **odd-chain fatty acids** and certain **amino acids**, allowing their entry into the **Krebs cycle**. *Dopamine to Norepinephrine* - This conversion is catalyzed by **dopamine beta-hydroxylase**, which requires **vitamin C** (ascorbate) and **copper** as cofactors, not vitamin B12. - It is a key step in the synthesis of **catecholamines** within the nervous system. *Propionyl CoA to methyl malonyl CoA* - This conversion is catalyzed by **propionyl-CoA carboxylase** and requires **biotin** as a cofactor, not vitamin B12. - This reaction is the first step in the metabolic pathway that leads to succinyl-CoA from odd-chain fatty acids. *Homocysteine to cysteine* - This conversion occurs via the **transsulfuration pathway** and requires **vitamin B6** (pyridoxal phosphate) as a cofactor, not vitamin B12. - The enzymes involved are **cystathionine β-synthase** and **cystathionine γ-lyase**, both B6-dependent. - Vitamin B12 is involved in the **remethylation** of homocysteine to methionine (not in transsulfuration to cysteine).

Q: Why is the citric acid cycle called an amphibolic pathway?

Metabolites are utilized in other pathways.. ***Metabolites are utilized in other pathways.*** - The citric acid cycle is termed **amphibolic** because it serves both catabolic (breakdown) and anabolic (synthetic) functions. - Its intermediates are constantly drawn off for biosynthesis of molecules like **amino acids**, **heme**, and **glucose**, meaning it's not solely degradative. *Both exergonic and endergonic reactions take place* - While both types of reactions do occur in many metabolic pathways, this is a general characteristic of metabolism and not specific to the definition of an **amphibolic pathway**. - The amphibolic nature specifically refers to the dual role in both **catabolism** and **anabolism**. *It can proceed in both forward and backward directions.* - This statement typically describes a **reversible pathway** or individual reversible reactions, not necessarily an amphibolic pathway. - The citric acid cycle is primarily an oxidative cycle that proceeds in a forward, cyclic direction under aerobic conditions. *The same enzymes can be used in reverse directions.* - While some individual enzymes within metabolic pathways can catalyze reversible reactions, this is not the defining characteristic of an **amphibolic pathway**. - The amphibolic designation refers to the overall pathway's contribution to both breakdown and synthesis of molecules.

Q: Which enzyme in the TCA cycle catalyzes the step where substrate-level phosphorylation occurs?

Succinate thiokinase. ***Succinate thiokinase*** - This enzyme (also known as **succinyl-CoA synthetase**) catalyzes the conversion of **succinyl-CoA** to **succinate**. - During this reaction, the energy released from breaking the **thioester bond** in succinyl-CoA is directly used to synthesize **GTP** (or ATP in some organisms) from GDP (or ADP) and inorganic phosphate, which is a classic example of **substrate-level phosphorylation**. *Isocitrate dehydrogenase* - This enzyme catalyzes the **oxidative decarboxylation** of isocitrate to $\alpha$-ketoglutarate. - This step produces **NADH** and **CO2** but does not involve substrate-level phosphorylation. *Malate dehydrogenase* - This enzyme catalyzes the oxidation of **L-malate** to **oxaloacetate** in the final step of the TCA cycle. - It produces **NADH** but does not involve the direct synthesis of ATP or GTP. *Aconitase* - This enzyme catalyzes the **isomerization** of **citrate** to **isocitrate** via an aconitate intermediate. - No energy is generated or consumed in the form of ATP/GTP during this rearrangement.

Q: Which of the following complications is commonly associated with mitral valve prolapse?

Infective endocarditis. Mitral valve prolapse (MVP) involves myxomatous degeneration of the mitral valve leaflets, which can create a rough surface predisposing to bacterial adhesion and subsequent infective endocarditis [1]. While the overall risk is low, patients with MVP and accompanying mitral regurgitation or thickened leaflets are at higher risk [1]. Patients with valvular heart disease are generally susceptible to bacterial endocarditis, often associated with procedures or dental hygiene [2]. Stroke - Although MVP can sometimes be associated with embolic events (e.g., from thrombi forming on the prolapsing valve), stroke is not considered a commonly associated complication. - The risk of stroke is generally higher in MVP patients with concomitant atrial fibrillation or other cardiovascular risk factors. Mitral stenosis - Mitral valve prolapse is characterized by the displacement of mitral valve leaflets into the left atrium during systole, which can lead to mitral regurgitation [3], not stenosis. - Mitral stenosis involves narrowing of the mitral valve orifice, usually due to rheumatic fever, which is a different pathophysiology [4]. Ventricular arrhythmia - While palpitations (often benign supraventricular ectopy) are common in MVP, clinically significant ventricular arrhythmias are less common. - Severe ventricular arrhythmias are more typically seen with significant underlying myocardial disease or severe mitral regurgitation causing left ventricular dysfunction.

Q: Helmet cells are characteristic of anemia of?

Hemolytic uremic syndrome (HUS). ***Hemolytic uremic syndrome*** - Helmet cells are **fragmented red blood cells** associated with **microangiopathic hemolytic anemia** [1], commonly seen in hemolytic uremic syndrome. - This condition frequently results in **thrombocytopenia** and acute renal failure. *Acanthocytosis* - Acanthocytosis is characterized by **spiky red blood cells** (acanthocytes) rather than helmet cells. - It is commonly associated with **liver disease** and **abetalipoproteinemia**, not hemolytic anemia. *Polysplenia* - Polysplenia is a condition involving multiple spleens but does not typically relate to the **formation of helmet cells**. - It may cause **asplenic complications**, but anemia characteristics do not include helmet cells. *Spherocytosis* - Spherocytosis involves the presence of **spherical red blood cells** rather than fragmented (helmet) cells. - It is associated with **hereditary conditions** like hereditary spherocytosis, which leads to increased hemolysis but not typically to helmet cells. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 596-597.

Q: What change is seen in the vessels during the initial stage of Raynaud's phenomenon?

No pathological changes (functional vasospasm only). ***No pathological changes (functional vasospasm only)*** - Raynaud's phenomenon, particularly **primary Raynaud's** (Raynaud's disease), is characterized by **functional vasospasm** of arterioles, especially in fingers and toes, in response to cold or stress [1]. - In its initial stages, there are no structural changes or pathological alterations within the vessel walls; the vasoconstriction is entirely **functional** [1]. *Thrombosis* - **Thrombosis** involves the formation of a blood clot within a vessel, obstructing blood flow. - While severe Raynaud's can, in rare cases, lead to digital ischemia and microthrombosis, it is **not the primary or initial change** seen in typical Raynaud's phenomenon. *Fibrinoid necrosis* - **Fibrinoid necrosis** is a type of vascular damage associated with severe autoimmune diseases or malignant hypertension, where fibrin and plasma proteins deposit in the vessel wall. - This is a **structural, irreversible change** and is not characteristic of the initial, functional vasospasm seen in Raynaud's phenomenon. *Hyaline sclerosis* - **Hyaline sclerosis** is a change in small arteries and arterioles, often seen in benign essential hypertension or as part of the aging process, where the vessel wall thickens and becomes hyaline (glassy) due to plasma protein leakage and fibrosis. - This represents a **chronic structural change** and is not the acute, intermittent, functional vasoconstriction defining the initial stage of Raynaud's. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 520-522.

Q: Which tract is responsible for the loss of proprioception and fine touch?

Dorsal column. ***Dorsal column*** - The **dorsal column-medial lemniscus pathway** is responsible for transmitting **fine touch**, **vibration**, and **proprioception** from the body to the cerebral cortex. - Damage to this tract (e.g., in **tabes dorsalis** or **vitamin B12 deficiency**) leads to a loss of these sensations. *Anterior spinothalamic tract* - This tract primarily conveys crude touch and pressure sensations. - While it carries tactile information, it does not transmit the fine discriminative touch or proprioception associated with the dorsal columns. *Lateral spinothalamic tract* - This pathway is responsible for transmitting **pain** and **temperature** sensations. - It does not play a role in proprioception or fine touch. *Corticospinal tract* - The **corticospinal tract** is a **motor pathway** responsible for voluntary movement. - It has no role in transmitting sensory information such as proprioception or fine touch.

Question 1

What is the classification of the Y chromosome?

Accepted Answer

Submetacentric

Answer

Metacentric

Answer

Acrocentric

Answer

None of the options

Question 2

Which bone has the maximum anatomical contribution to the floor of the orbit?

Accepted Answer

Maxillary

Answer

Zygomatic

Answer

Sphenoid

Answer

Palatine

Question 3

Waldeyer's fascia lies?

Accepted Answer

Behind the rectum.

Answer

In front of the bladder.

Answer

Between the bladder and uterus.

Answer

Between the uterus and rectum.

Question 4

The cofactor vitamin B12 is required for the following conversion:

Accepted Answer

Methyl malonyl CoA to succinyl CoA

Answer

Dopamine to Norepinephrine

Answer

Propionyl CoA to methyl malonyl CoA

Answer

Homocysteine to cysteine

Question 5

Why is the citric acid cycle called an amphibolic pathway?

Accepted Answer

Metabolites are utilized in other pathways.

Answer

Both exergonic and endergonic reactions take place

Answer

It can proceed in both forward and backward directions.

Answer

The same enzymes can be used in reverse directions.

Question 6

Which enzyme in the TCA cycle catalyzes the step where substrate-level phosphorylation occurs?

Accepted Answer

Succinate thiokinase

Answer

Isocitrate dehydrogenase

Answer

Malate dehydrogenase

Answer

Aconitase

Question 7

Which of the following complications is commonly associated with mitral valve prolapse?

Accepted Answer

Infective endocarditis

Answer

Ventricular arrhythmia

Answer

Stroke

Answer

Mitral stenosis

Question 8

Helmet cells are characteristic of anemia of?

Accepted Answer

Hemolytic uremic syndrome (HUS)

Answer

Disseminated intravascular coagulation (DIC)

Answer

Thrombotic thrombocytopenic purpura (TTP)

Answer

Autoimmune hemolytic anemia (AIHA)

Question 9

What change is seen in the vessels during the initial stage of Raynaud's phenomenon?

Accepted Answer

No pathological changes (functional vasospasm only)

Answer

Thrombosis

Answer

Fibrinoid necrosis

Answer

Hyaline sclerosis

Question 10

Which tract is responsible for the loss of proprioception and fine touch?

Accepted Answer

Dorsal column

Answer

Anterior spinothalamic tract

Answer

Lateral spinothalamic tract

Answer

Corticospinal tract

NEET-PG 2012

Anatomy

Biochemistry

Internal Medicine

Pathology

Physiology