Biochemistry
3 questionsThe rate-limiting step in glycolysis is catalyzed by?
Which reaction requires Vitamin B1?
Cell-matrix adhesions are mediated by?
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 31: The rate-limiting step in glycolysis is catalyzed by?
- A. Phosphofructokinase (Correct Answer)
- B. Enolase
- C. Glucokinase
- D. Pyruvate kinase
Explanation: ***Phosphofructokinase*** - **Phosphofructokinase-1 (PFK-1)** is the primary regulatory enzyme and **rate-limiting step** in glycolysis. - It catalyzes the irreversible phosphorylation of **fructose-6-phosphate to fructose-1,6-bisphosphate**, a crucial commitment step. *Enolase* - **Enolase** catalyzes the conversion of **2-phosphoglycerate to phosphoenolpyruvate** in glycolysis. - While essential for glycolysis, it is not the rate-limiting step. *Glucokinase* - **Glucokinase** catalyzes the phosphorylation of glucose to **glucose-6-phosphate** in the liver and pancreatic beta cells. - This is the first step in glycolysis but is not the rate-limiting step for the entire pathway once glucose has entered the cell. *Pyruvate kinase* - **Pyruvate kinase** catalyzes the final step of glycolysis, converting **phosphoenolpyruvate to pyruvate**. - Although it is a regulated enzyme, it is not the primary rate-limiting step that controls the overall flux through the glycolytic pathway.
Question 32: Which reaction requires Vitamin B1?
- A. None of the options
- B. Oxidative decarboxylation (Correct Answer)
- C. Carboxylation
- D. Transamination
Explanation: ***Oxidative decarboxylation*** - Vitamin B1, in its active form **thiamine pyrophosphate (TPP)**, is a crucial coenzyme for enzymes catalyzing **oxidative decarboxylation** reactions. - Key examples include the **pyruvate dehydrogenase complex** and **alpha-ketoglutarate dehydrogenase complex**, essential for cellular respiration and the citric acid cycle. *Transamination* - This type of reaction, involving the transfer of an **amino group**, primarily requires **pyridoxal phosphate (PLP)**, the active form of **Vitamin B6**. - It is vital for amino acid metabolism but does not utilize Vitamin B1. *Carboxylation* - **Carboxylation** reactions, which add a carboxyl group to a substrate, typically require **biotin** (Vitamin B7) as a coenzyme. - Examples include pyruvate carboxylase and acetyl-CoA carboxylase, which are not dependent on Vitamin B1. *None of the options* - As **oxidative decarboxylation** specifically requires Vitamin B1, this option is incorrect. - The other listed reactions depend on different vitamins as coenzymes.
Question 33: Cell-matrix adhesions are mediated by?
- A. Integrins (Correct Answer)
- B. Selectins
- C. Calmodulin
- D. Cadherins
Explanation: ***Integrins*** - **Integrins** are transmembrane receptors that mediate cell adhesion to the **extracellular matrix (ECM)**, linking it to the cell's cytoskeleton. - They bind to various ECM components like **fibronectin**, **collagen**, and **laminin**. *Cadherins* - **Cadherins** are primarily involved in **cell-to-cell adhesion**, forming junctions like **adherens junctions** and **desmosomes**. - They are **calcium-dependent adhesion molecules** that do not directly bind to the extracellular matrix. *Selectins* - **Selectins** are cell adhesion molecules involved in **leukocyte rolling** and **adhesion to endothelial cells** during inflammation. - They mediate **transient cell-to-cell interactions**, not cell-matrix adhesion. *Calmodulin* - **Calmodulin** is a **calcium-binding protein** that acts as a signal transducer, regulating various intracellular processes. - It is involved in **calcium-dependent signaling pathways** and enzyme activation, not cell adhesion.
Community Medicine
1 questionsIn a measles outbreak, measles vaccine can be given to infants at what age range:
NEET-PG 2012 - Community Medicine NEET-PG Practice Questions and MCQs
Question 31: In a measles outbreak, measles vaccine can be given to infants at what age range:
- A. 2-3 months
- B. 3-5 months
- C. 2-7 months
- D. 6-9 months (Correct Answer)
Explanation: ***6-9 months*** - During a **measles outbreak**, infants as young as **6 months** can receive an early dose of the measles vaccine to provide protection. - This early vaccination is crucial in high-risk situations, even though the standard first dose is typically given at **12-15 months** of age. *2-3 months* - Administering the measles vaccine at **2-3 months** is generally avoided because of the presence of persistent **maternal antibodies**. - These antibodies can interfere with the infant's immune response to the vaccine, making it less effective. *3-5 months* - Similar to the 2-3 month range, **maternal antibodies** are still likely present and at sufficiently high levels in infants aged 3-5 months. - This interference reduces the vaccine's efficacy and the likelihood of developing a robust, lasting immune response. *2-7 months* - While this range includes the accepted 6-month age for early vaccination, infants under **6 months** still pose a challenge due to **maternal antibody interference**. - Combining these ages into a single range doesn't differentiate between the reduced efficacy in younger infants versus the permissible early vaccination at 6 months and older during an outbreak.
Internal Medicine
1 questionsWhat is the most common site of gastrointestinal stromal tumors (GISTs)?
NEET-PG 2012 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 31: What is the most common site of gastrointestinal stromal tumors (GISTs)?
- A. Ileum
- B. Esophagus
- C. Colon
- D. Stomach (Correct Answer)
Explanation: Stomach - The stomach is the most common site for gastrointestinal stromal tumors (GISTs), accounting for approximately 60-70% of cases. - GISTs in the stomach often present with symptoms like abdominal pain or bleeding and are associated with mutations in the KIT gene. Ileum - Although GISTs can occur in the ileum, they are far less common than those found in the stomach, representing about 10-15% of cases [1]. - GISTs in the ileum tend to present differently, often with intestinal obstruction or pain [1]. Esophagus - Esophageal GISTs are rare and account for only about 5% of GIST cases, making them an uncommon location. - Symptoms are usually related to dysphagia or chest pain, not typical for GISTs arising from more common sites. Colon - Although GISTs can occur in the colon, their frequency is much lower compared to the stomach and represents a small percentage of cases. - Clinical features in colonic GISTs can mimic other colorectal tumors, often causing obstruction or bleeding rather than classic GIST symptoms.
Microbiology
1 questionsWhat is the primary virulence factor of Neisseria gonorrhoeae?
NEET-PG 2012 - Microbiology NEET-PG Practice Questions and MCQs
Question 31: What is the primary virulence factor of Neisseria gonorrhoeae?
- A. All of the above are incorrect
- B. Pili (fimbriae) (Correct Answer)
- C. Endotoxin (lipooligosaccharide)
- D. Exotoxin
Explanation: ***Pili (fimbriae)*** - **Pili are the PRIMARY virulence factor** of *Neisseria gonorrhoeae*, essential for **initial attachment and colonization** of urogenital mucosa - Enable bacteria to **adhere to non-ciliated epithelial cells**, resisting mechanical clearance by urination and secretions - Undergo **antigenic variation** to evade host immune responses - Without pili, *N. gonorrhoeae* cannot establish infection *Endotoxin (lipooligosaccharide)* - *N. gonorrhoeae* possesses **LOS (lipooligosaccharide)** which causes inflammation and tissue damage - While important for pathogenesis, it is a **secondary virulence factor** - LOS contributes to symptoms but cannot cause infection without prior colonization via pili *Exotoxin* - *N. gonorrhoeae* does **not produce significant exotoxins** - Pathogenicity is mediated through **adherence factors (pili), LOS, and surface proteins** rather than secreted protein toxins - This is not a mechanism of gonococcal virulence *All of the above are incorrect* - This statement is false as **pili (fimbriae)** are definitively the primary virulence factor for *N. gonorrhoeae*
Pathology
2 questionsTransitional cell carcinoma of the bladder is associated with which of the following?
What is the term for a localized malformation composed of an excessive but disorganized arrangement of cells and tissues indigenous to the site?
NEET-PG 2012 - Pathology NEET-PG Practice Questions and MCQs
Question 31: Transitional cell carcinoma of the bladder is associated with which of the following?
- A. Malaria
- B. Schistosomiasis
- C. None of the options (Correct Answer)
- D. Ascariasis
Explanation: ***Schistosomiasis*** - Schistosomiasis, particularly from *Schistosoma haematobium*, is a well-known risk factor for **transitional cell carcinoma of the bladder** due to chronic irritation and inflammation [1]. - The association arises due to the **presence of eggs in the bladder**, leading to calcification and eventually cancer development. *Malaria* - Malaria is primarily associated with **hemolytic anemia** and does not have a direct correlation with **bladder cancer**. - Its causative agents, *Plasmodium* species, do not typically lead to **urological malignancies** like transitional cell carcinoma. *Ascarasis* - Ascarasis, caused by *Ascaris lumbricoides*, primarily affects the **intestines** and is more associated with gastrointestinal issues. - There is no significant link between ascarasis and the **development of bladder cancer**. *Any of d above* - As this option suggests all listed conditions, it incorrectly implies that **malaria** and **ascarasis** are linked to bladder cancer, which they are not. - Transitional cell carcinoma is specifically associated with **schistosomiasis**, making this option misleading. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Lower Urinary Tract and Male Genital System, pp. 968-970.
Question 32: What is the term for a localized malformation composed of an excessive but disorganized arrangement of cells and tissues indigenous to the site?
- A. Hamartoma (Correct Answer)
- B. Malignant tumor
- C. Choristoma
- D. None of the options
Explanation: ***Hamartoma*** - A **hamartoma** is an overgrowth of cells and tissues that are normally found in the affected area, but in a disordered fashion, creating a tumor-like growth [1]. - It's a **benign (non-cancerous)** lesion, often congenital, that grows at the same rate as the surrounding tissues. *Malignant tumor* - A **malignant tumor** is characterized by uncontrolled cell growth that invades surrounding tissues and can metastasize to distant sites. - Unlike a hamartoma, a malignant tumor consists of **abnormal, dysplastic cells** that do not resemble the normal tissues of the organ. *Choristoma* - A choristoma is a **benign tumor-like growth** consisting of normal cells or tissues that are **heterotopic**, meaning they are located in an abnormal site. - An example is the presence of pancreatic tissue in the wall of the stomach, which is normal tissue in an abnormal location, unlike a hamartoma which has normal tissue in the correct location but in a disorganized manner. *None of the options* - This option is incorrect because **hamartoma** accurately describes the overgrowth of a skin structure at a localized region made of normal, but disorganized, tissue [1]. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Disorders Involving Inflammatory And Haemopoietic Cells, pp. 651-652.
Pediatrics
1 questionsWhat is the most common presentation of tuberculosis (TB) in children?
NEET-PG 2012 - Pediatrics NEET-PG Practice Questions and MCQs
Question 31: What is the most common presentation of tuberculosis (TB) in children?
- A. Abscess
- B. Consolidation
- C. Hilar adenopathy (Correct Answer)
- D. CNS tuberculosis
Explanation: ***Hilar adenopathy*** - **Hilar adenopathy** is the most common radiographic finding in children with **primary tuberculosis**, reflecting lymph node involvement. - This is often accompanied by a small parenchymal lesion, forming the **Ghon complex**. *Abscess* - While TB can cause abscesses (e.g., cold abscesses in bone or soft tissue), it's not the **most common initial presentation** of primary childhood TB. - Abscess formation suggests a more **advanced or extrapulmonary** manifestation. *Consolidation* - **Consolidation** can be seen in adult-type or progressive primary TB, but it is less frequent than hilar adenopathy as the **initial presentation** in children. - It indicates **pneumonia-like changes** due to parenchymal inflammation. *CNS tuberculosis* - **Central Nervous System (CNS) tuberculosis** (e.g., tuberculous meningitis or tuberculoma) is a severe, extrapulmonary form of TB. - It is a **serious complication** rather than the most common initial presentation in children.
Radiology
1 questionsHalf-life of iodine-131 is
NEET-PG 2012 - Radiology NEET-PG Practice Questions and MCQs
Question 31: Half-life of iodine-131 is
- A. 8 days (Correct Answer)
- B. 8 hours
- C. 8 weeks
- D. 8 months
Explanation: ***8 days*** - The half-life of **iodine-131** is approximately 8.02 days, which makes it suitable for both diagnostic imaging and therapeutic applications in thyroid conditions. - This specific half-life allows sufficient time for the isotope to localize in the thyroid gland and deliver a therapeutic dose, while also ensuring it clears from the body relatively quickly to minimize long-term radiation exposure. *8 hours* - A half-life of 8 hours would be too short for many therapeutic applications of iodine-131, as it would decay too rapidly to deliver an effective dose to the thyroid. - Isotopes with such short half-lives are typically used for diagnostic imaging where rapid clearance and minimal patient exposure are paramount, such as **technetium-99m**. *8 weeks* - A half-life of 8 weeks would be excessively long for clinical use of iodine-131, leading to prolonged radiation exposure for the patient. - Such long half-lives increase the risk of adverse effects from cumulative radiation, making it unsuitable for routine diagnostic or therapeutic procedures. *8 months* - A half-life of 8 months is impractically long for any medical application requiring regular administration, as it would lead to very high and persistent radiation doses. - This duration would result in significant and unacceptable long-term radiation hazards, making its use unfeasible for imaging or therapy.