Biochemistry
1 questionsWhat is the mechanism of conversion of trypsinogen to trypsin?
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 411: What is the mechanism of conversion of trypsinogen to trypsin?
- A. Hydrolysis
- B. Phosphorylation
- C. Removal of part of protein (Correct Answer)
- D. Removal of Carboxyl group
Explanation: ***Removal of part of protein*** - The conversion of **trypsinogen to trypsin** is an example of **proteolytic activation**, where a specific part of the inactive precursor (zymogen) is cleaved off. - This cleavage occurs at the N-terminus of trypsinogen by **enteropeptidase (or enterokinase)** in the duodenum, exposing the active site and forming active trypsin. *Hydrolysis* - While the removal of a part of the protein involves **hydrolysis of peptide bonds**, this option is too general. - It does not specify the selective nature of the cleavage that leads to activation, nor the fact that it's a specific segment being removed. *Phosphorylation* - **Phosphorylation** is a common mechanism for regulating enzyme activity, but it involves the addition of a **phosphate group**, not the removal of a protein segment. - This process is typically mediated by kinases and does not activate trypsinogen. *Removal of Carboxyl group* - The activation of trypsinogen involves the removal of a small N-terminal peptide, not specifically the removal of a **carboxyl group** from the protein. - While enzymatic cleavage does involve breaking peptide bonds, stating "removal of carboxyl group" is imprecise and does not accurately describe the mechanism.
Pathology
2 questionsWhat is a distinguishing feature of reticulocytes?
Which of the following statements is true regarding the Duffy Fy(a-b-) blood group?
NEET-PG 2015 - Pathology NEET-PG Practice Questions and MCQs
Question 411: What is a distinguishing feature of reticulocytes?
- A. Slightly larger in size than RBCs
- B. Presence of residual RNA and ribosomes (Correct Answer)
- C. Mature in bone marrow
- D. Constitute approximately 1% of the red cells
Explanation: ***Presence of residual RNA and ribosomes*** - This is the **defining and most distinguishing feature** of reticulocytes that differentiates them from mature red blood cells. - Reticulocytes contain residual **ribosomal RNA** and other organelles that are lost when they mature into erythrocytes. - This residual RNA forms a **reticular (network-like) pattern** when stained with supravital stains like **new methylene blue** or **brilliant cresyl blue**, which is the basis for their name and identification. - The presence of RNA allows for **reticulocyte counting**, an important marker of bone marrow erythropoietic activity. *Slightly larger in size than RBCs* - While reticulocytes may be slightly larger (polychromatophilic appearance), size variation is **not specific** and overlaps significantly with mature RBCs. - Size is not a reliable distinguishing feature and is not used for identification or counting. *Mature in bone marrow* - Reticulocytes are **released from the bone marrow** as immature red cells and complete their maturation in the **peripheral circulation** over 24-48 hours. - They do not fully mature in the bone marrow; their presence in peripheral blood is normal. *Constitute approximately 1% of the red cells* - Normal reticulocyte count is **0.5-2%** (or approximately 1%) of total red blood cells in healthy adults. - This is a **population characteristic** indicating normal erythropoietic activity, not a distinguishing cellular feature.
Question 412: Which of the following statements is true regarding the Duffy Fy(a-b-) blood group?
- A. lacks H- antigen
- B. lacks A-antigen
- C. All of the options
- D. lacks Fy(b) antigen (Correct Answer)
Explanation: ***lacks Fy(b) antigen*** - The **Duffy Fy(a-b-)** phenotype indicates absence of both Fy<sup>a</sup> and Fy<sup>b</sup> antigens on red blood cells. - Since the phenotype is **Fy(a-b-)**, it definitively lacks the **Fy<sup>b</sup> antigen** (indicated by the "b-" notation). - This phenotype is common in people of **African descent** and confers natural **resistance to Plasmodium vivax malaria**, as these antigens serve as receptors for the parasite to enter RBCs. *lacks H- antigen* - The **H antigen** belongs to the **H/h blood group system** and is a precursor to A and B antigens in the ABO system. - The absence of H antigen (Bombay phenotype - Oh) is completely **unrelated to the Duffy blood group system**. - Duffy antigens are on the **DARC (Duffy Antigen Receptor for Chemokines)** protein, distinct from the H antigen. *lacks A-antigen* - The **A antigen** is part of the **ABO blood group system** and defines blood types A and AB. - The Duffy blood group system is **genetically and structurally independent** from the ABO system. - Having Fy(a-b-) phenotype does not affect A antigen expression. *All of the options* - This is incorrect because the Duffy Fy(a-b-) phenotype **specifically refers only to the absence of Duffy antigens** (Fy<sup>a</sup> and Fy<sup>b</sup>). - It has **no relationship** with A, B, or H antigens, which belong to different blood group systems controlled by different genes on different chromosomes.
Pediatrics
1 questionsWhat is the typical lifespan of neonatal red blood cells (RBCs)?
NEET-PG 2015 - Pediatrics NEET-PG Practice Questions and MCQs
Question 411: What is the typical lifespan of neonatal red blood cells (RBCs)?
- A. 120-150 days
- B. 150-200 days
- C. 60-90 days (Correct Answer)
- D. 90-120 days
Explanation: ***60-90 days*** - The typical lifespan of **neonatal red blood cells (RBCs)** is **60-90 days**, which is **shorter than adult RBCs** (120 days). - This reduced lifespan is due to **increased membrane fragility**, **higher metabolic rate**, and **immature enzyme systems** in neonatal erythrocytes. - Neonatal RBCs contain more **fetal hemoglobin (HbF)** and have structural differences that contribute to their shorter survival. - This shorter lifespan contributes to the **physiological anemia of infancy** seen in the first few months of life. *90-120 days* - This range represents the typical lifespan of **adult RBCs**, not neonatal RBCs. - Neonatal RBCs have a **demonstrably shorter lifespan** compared to adult erythrocytes. - Confusing adult and neonatal RBC lifespans is a common error in clinical practice. *120-150 days* - This range is **longer than even adult RBC lifespan** (typically 120 days). - This would be **highly atypical** for any normal erythrocyte population. *150-200 days* - This represents an **abnormally prolonged** RBC lifespan not seen in normal physiology. - Such extended survival would suggest **pathological conditions** affecting RBC destruction or measurement error.
Pharmacology
5 questionsHigh volume of distribution is primarily determined by:
Which of the following statements represents the most clinically significant aspect of drug metabolism?
Which of the following is an example of topical administration producing only local effects (not systemic)?
Which of the following pairs are considered physiological antagonists in pharmacology?
Which of the following is not a common side effect of clonidine?
NEET-PG 2015 - Pharmacology NEET-PG Practice Questions and MCQs
Question 411: High volume of distribution is primarily determined by:
- A. High lipid solubility (Correct Answer)
- B. High plasma protein binding
- C. Elimination rate
- D. Half-life of the drug
Explanation: ***High lipid solubility***- Highly **lipid-soluble** drugs readily cross biological membranes and distribute extensively into tissues, including adipose tissue, CNS, and intracellular compartments, leading to a **high volume of distribution (Vd)** [1, 2].- This property allows the drug to move out of the bloodstream and into various body compartments, increasing the apparent volume in which the drug is dissolved [1].*High plasma protein binding*- **High plasma protein binding** generally **restricts** drug distribution to tissues because only the **unbound (free) fraction** can diffuse across capillary membranes into interstitial fluid and cells [1].- This typically leads to a **lower Vd**, as the drug is largely retained within the plasma compartment.*Elimination rate*- The **elimination rate** determines how quickly the drug is removed from the body, affecting the **duration of action** rather than the extent of distribution.- It influences drug concentration changes over time but does not directly determine the physical space (volume) into which the drug distributes.*Half-life of the drug*- The **half-life (t½)** is the time required for drug concentration to reduce by half, and it is **determined by** both Vd and clearance (t½ = 0.693 × Vd/CL).- Half-life is a **consequence** of Vd and clearance, not a primary determinant of how widely a drug distributes [3].
Question 412: Which of the following statements represents the most clinically significant aspect of drug metabolism?
- A. Most common enzyme involved is CYP 3A4/5 (Correct Answer)
- B. Glucuronidation is a phase II reaction
- C. Reduction is a phase I reaction
- D. Cytochrome P450 is involved in phase I reactions
Explanation: ***Most common enzyme involved is Cyp 3A4/5*** - CYP3A4/5 is the **most abundant and clinically significant** cytochrome P450 enzyme, responsible for metabolizing approximately **50% of all clinically used drugs**. - Its widespread involvement means variations in its activity (due to **genetics, drug interactions, or disease**) have a major impact on drug efficacy and toxicity. *Glucuronidation is a phase II reaction* - While correct that glucuronidation is a **Phase II metabolic reaction**, this statement describes a biochemical classification rather than a clinically significant aspect compared to the involvement of CYP3A4/5. - Phase II reactions generally involve **conjugation** to increase water solubility and facilitate excretion, but they do not collectively account for as many drug interactions as CYP3A4/5 alone. *Reduction is a phase I reaction* - This statement is factually correct as **reduction** is indeed a **Phase I metabolic reaction**. - However, it represents a generic classification of a metabolic pathway and doesn't highlight the specific clinical importance or prevalence of a particular enzyme or reaction in drug metabolism. *Cytochrome P450 is involved in phase I reactions* - This is true; the **cytochrome P450 system** is the primary enzyme system for **Phase I metabolism**, which introduces or exposes polar groups to make drugs more reactive. - While fundamentally important, this statement is too broad; it does not specify the most clinically significant *aspect* or *enzyme* within the P450 system compared to directly identifying CYP3A4/5.
Question 413: Which of the following is an example of topical administration producing only local effects (not systemic)?
- A. Topical corticosteroid cream (Correct Answer)
- B. Sublingual nitroglycerin
- C. Transdermal patch
- D. Rectal diazepam
Explanation: ***Topical corticosteroid cream*** - When applied to the skin for conditions like dermatitis, topical corticosteroids primarily exert their effects at the site of application, reducing **local inflammation** and itching. - While systemic absorption can occur with potent steroids over large areas, typical use aims for **localized action** without significant systemic effects. *Sublingual nitroglycerin* - This route is designed for **rapid systemic absorption** through the oral mucosa, bypassing first-pass metabolism to quickly treat angina. - The goal is a **widespread vasodilatory effect** throughout the body, not a local one within the mouth. *Transdermal patch* - Transdermal patches, such as those for nicotine or fentanyl, are specifically designed to deliver medication **systemically** through the skin into the bloodstream over a prolonged period. - They provide a **sustained release** and systemic therapeutic effect throughout the body. *Rectal diazepam* - Administered rectally, diazepam is absorbed into the systemic circulation to produce **CNS effects** such as sedation, anxiolysis, or anticonvulsant activity. - Although the administration is local, the intended clinical effect is **systemic** and widespread throughout the body.
Question 414: Which of the following pairs are considered physiological antagonists in pharmacology?
- A. Adrenaline and Isoprenaline
- B. Isoprenaline and Propranolol
- C. Histamine and Adrenaline (Correct Answer)
- D. All of the options
Explanation: ***Histamine and Adrenaline*** - **Physiological antagonism** occurs when two drugs produce opposite effects by acting on different receptors or pathways. - **Histamine** causes bronchoconstriction and vasodilation, while **adrenaline** causes bronchodilation and vasoconstriction, counteracting each other's effects through different mechanisms. *Adrenaline and Isoprenaline* - Both **adrenaline** and **isoprenaline** are **adrenergic agonists** that produce similar physiological effects, primarily through beta-adrenergic receptor activation. - They are not physiological antagonists but rather have **synergistic** or similar pharmacological actions. *Isoprenaline and Propranolol* - **Isoprenaline** is a **beta-adrenergic agonist**, while **propranolol** is a **beta-adrenergic antagonist**. - This is an example of **pharmacological antagonism (receptor antagonism)**, where one drug blocks the effect of another at the same receptor site, rather than physiological antagonism.
Question 415: Which of the following is not a common side effect of clonidine?
- A. Xerostomia
- B. Sedation
- C. Diarrhea (Correct Answer)
- D. Impotency
Explanation: ***Diarrhea*** - **Clonidine** commonly causes **constipation**, not diarrhea, due to its **alpha-2 adrenergic agonist** effects, which decrease gastrointestinal motility. - Diarrhea is not typically associated with clonidine's mechanism of action or adverse effect profile. *Xerostomia* - **Xerostomia** (dry mouth) is a very common side effect of **clonidine** occurring in up to 40% of patients. - This results from **alpha-2 agonist** activity that reduces sympathetic stimulation of salivary gland secretions. - This symptom can significantly impact patient compliance and quality of life. *Sedation* - **Sedation** is a frequent side effect of **clonidine**, particularly when initiating treatment or increasing dosage, because it acts as an **alpha-2 agonist** in the central nervous system, reducing sympathetic outflow and promoting drowsiness. - Patients are often advised to avoid driving or operating heavy machinery until they know how the medication affects them. *Impotency* - **Impotency** or **erectile dysfunction** is a recognized and common sexual side effect of **clonidine**, which can interfere with quality of life and adherence to treatment for hypertension. - This effect is related to the drug's impact on the autonomic nervous system and vascular tone through central alpha-2 agonism.
Physiology
1 questionsFastest receptor mediated action is through?
NEET-PG 2015 - Physiology NEET-PG Practice Questions and MCQs
Question 411: Fastest receptor mediated action is through?
- A. Intrinsic ion channels (Correct Answer)
- B. Intracellular receptors
- C. Cell surface receptors
- D. Receptor tyrosine kinases
Explanation: ***Intrinsic ion channels*** - Receptors that are also **ion channels** (ligand-gated ion channels) allow direct and rapid ion flow across the membrane upon ligand binding, leading to immediate changes in membrane potential. - This direct mechanism bypasses complex intracellular signaling cascades, resulting in the **fastest cellular response** compared to other receptor types. *Cell surface receptors* - This is a broad category that includes **G protein-coupled receptors** and **receptor tyrosine kinases**, which typically involve more complex and slower signaling pathways. - While located on the cell surface, not all receptors in this category mediate action as quickly as intrinsic ion channels. *Receptor tyrosine kinases* - These receptors initiate signaling by **phosphorylating tyrosine residues** on target proteins, triggering a cascade of intracellular events that take time to manifest. - Their action involves **multiple phosphorylation steps** and protein interactions, making their response slower compared to direct ion channels. *Intracellular receptors* - These receptors, such as **steroid hormone receptors**, are located in the cytoplasm or nucleus and require their ligands to diffuse across the cell membrane. - The activated receptor then typically translocates to the nucleus to regulate gene transcription, a process that is much **slower** due to gene expression and protein synthesis.