Biochemistry
3 questionsWhat is the mechanism of conversion of trypsinogen to trypsin?
Rate limiting enzyme in bile acid synthesis?
Enzyme activity is expressed as?
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 421: 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.
Question 422: Rate limiting enzyme in bile acid synthesis?
- A. Desmolase
- B. 21α-hydroxylase
- C. 7α-hydroxylase (Correct Answer)
- D. 12α-hydroxylase
Explanation: ***7α-hydroxylase*** - This enzyme, specifically **cholesterol 7α-hydroxylase**, catalyzes the first and rate-limiting step in the classic pathway of **bile acid synthesis**, converting cholesterol to 7α-hydroxycholesterol. - Its activity is tightly regulated, primarily by the availability of cholesterol and feedback inhibition by bile acids, making it a key control point. *Desmolase* - **Cholesterol desmolase** (CYP11A1) is the rate-limiting enzyme in **steroid hormone synthesis** in the adrenal glands, converting cholesterol to pregnenolone. - It is not involved in the committed steps of bile acid synthesis from cholesterol. *21α-hydroxylase* - **21α-hydroxylase** (CYP21A2) is crucial in the synthesis of **cortisol and aldosterone** from progesterone and 17-hydroxyprogesterone, respectively. - Deficiency in this enzyme is the most common cause of **congenital adrenal hyperplasia**, but it has no direct role in bile acid synthesis. *12α-hydroxylase* - **12α-hydroxylase** (CYP8B1) is an enzyme involved in the later steps of bile acid synthesis, specifically in the formation of **cholic acid** from 7α-hydroxy-4-cholesten-3-one. - While essential for synthesizing primary bile acids, it is not the *rate-limiting enzyme* for the overall pathway; 7α-hydroxylase holds that distinction.
Question 423: Enzyme activity is expressed as?
- A. Millimoles/lit
- B. Milli gm/lit
- C. Mg/dl
- D. Micromoles/min (Correct Answer)
Explanation: ***Micromoles/min*** - Enzyme activity is typically measured by the rate at which an enzyme converts its **substrate into product**. - This rate is often expressed as the amount of product formed (e.g., **micromoles**) or substrate consumed per unit of time (e.g., **per minute**). *Millimoles/lit* - This unit expresses **concentration** (moles per liter) rather than a rate of reaction. - While enzyme reactions involve changes in substrate/product concentration, this unit alone does not describe the **activity or catalytic speed** of the enzyme. *Milli gm/lit* - This unit also expresses **concentration by mass** (milligrams per liter), not enzyme activity. - It does not account for the **time-dependent nature** of enzyme catalysis or the molar quantity of reactants/products. *Mg/dl* - This unit represents **concentration by mass** (milligrams per deciliter), commonly used for measuring substances like glucose or cholesterol in blood. - It is not appropriate for expressing the **catalytic rate or activity** of an enzyme.
Forensic Medicine
1 questionsWhich of the following statements is true about cadaveric spasm?
NEET-PG 2015 - Forensic Medicine NEET-PG Practice Questions and MCQs
Question 421: Which of the following statements is true about cadaveric spasm?
- A. Occurs immediately at the moment of death. (Correct Answer)
- B. May develop several hours after death.
- C. Develops only in certain muscle groups.
- D. Can affect any muscle in the body.
Explanation: ***Occurs immediately at the moment of death.*** - **Cadaveric spasm** is a rare form of muscle stiffening that occurs **instantly** at the moment of death, without the flaccid stage seen in rigor mortis. - This is the **primary defining characteristic** that distinguishes cadaveric spasm from all other postmortem changes. - It is typically associated with deaths involving **intense emotional stress**, fear, or extreme physical exertion just before death. *May develop several hours after death.* - This statement describes **rigor mortis**, which is the stiffening of muscles that typically begins 2-6 hours after death. - Cadaveric spasm is distinct from rigor mortis due to its **immediate onset**. *Develops only in certain muscle groups.* - While this statement has some validity (cadaveric spasm is typically **localized** to specific muscle groups like hands or limbs that were under extreme tension), it is not the **best answer**. - The key distinguishing feature of cadaveric spasm is its **immediate onset at death**, not merely its localized distribution. - Many postmortem changes can be localized; what makes cadaveric spasm unique is its instantaneous occurrence. *Can affect any muscle in the body.* - This is too broad and inaccurate. Cadaveric spasm is characteristically **localized or regional**, not generalized. - It typically involves muscles that were under **extreme voluntary contraction** at the moment of death (e.g., clutching a weapon, grasping an object). - Unlike rigor mortis, which eventually affects all muscles, cadaveric spasm remains confined to specific muscle groups.
Internal Medicine
1 questionsWhich of the following is a cause of post-transplantation hypertension? I. Rejection II. Cyclosporine nephrotoxicity III. Renal transplant artery stenosis (RTAS) IV. Recurrent disease in the allograft. Select the correct option.
NEET-PG 2015 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 421: Which of the following is a cause of post-transplantation hypertension? I. Rejection II. Cyclosporine nephrotoxicity III. Renal transplant artery stenosis (RTAS) IV. Recurrent disease in the allograft. Select the correct option.
- A. None of the above are correct causes.
- B. I, II, and IV are correct causes.
- C. I and III are correct causes.
- D. All of the options are correct causes of post-transplantation hypertension. (Correct Answer)
Explanation: ***All of the options are correct causes of post-transplantation hypertension.*** - Post-transplantation hypertension often has a multifactorial etiology, with **rejection**, **cyclosporine nephrotoxicity**, **renal transplant artery stenosis (RTAS)**, and **recurrent disease in the allograft** all being significant contributors. - Each of these conditions can lead to mechanisms that elevate blood pressure, such as **renal ischemia**, activation of the **renin-angiotensin system**, and inflammatory responses affecting renal function. *I, II, and IV are correct causes.* - This option is incorrect because it excludes **renal transplant artery stenosis (RTAS)** (III), which is a well-established cause of secondary hypertension in transplant recipients due to reduced blood flow to the allograft. - **RTAS** activates the renin-angiotensin-aldosterone system (RAAS), leading to **vasoconstriction** and **sodium retention**, contributing to hypertension. *I and III are correct causes.* - This option is incorrect as it omits other crucial causes like **cyclosporine nephrotoxicity** (II) and **recurrent disease in the allograft** (IV), both of which are documented contributors to post-transplantation hypertension. - **Cyclosporine nephrotoxicity** causes afferent arteriolar vasoconstriction and glomerulosclerosis, directly increasing blood pressure. *None of the above are correct causes.* - This option is incorrect because **rejection**, **cyclosporine nephrotoxicity**, **renal transplant artery stenosis (RTAS)**, and **recurrent disease in the allograft** are all recognized and significant causes of post-transplantation hypertension. - Each condition has distinct pathological mechanisms that contribute to **elevated blood pressure** in transplant recipients.
Pharmacology
5 questionsWhich of the following conditions is not associated with an increased risk of neuropathy caused by Isoniazid (INH)?
What is the best method for treating methanol poisoning?
Interstitial nephritis is associated with all of the following medications except:
What is the classification of Lorcaserin?
What is the half-life of nicotine in blood?
NEET-PG 2015 - Pharmacology NEET-PG Practice Questions and MCQs
Question 421: Which of the following conditions is not associated with an increased risk of neuropathy caused by Isoniazid (INH)?
- A. Uremia
- B. Diabetes mellitus
- C. Poor nutrition
- D. Hyperthyroidism (Correct Answer)
Explanation: ***Hyperthyroidism*** - **Hyperthyroidism** is not typically associated with an increased risk of isoniazid-induced neuropathy. The neuropathy due to INH is primarily linked to **pyridoxine (vitamin B6) deficiency**. - While hyperthyroidism can cause its own set of neurological symptoms, it does not directly impair pyridoxine metabolism or exacerbate INH's neurotoxic effects. *Uremia* - **Uremia** (renal failure) can increase the risk of INH-induced neuropathy due to impaired drug excretion, leading to higher plasma concentrations of INH and its metabolites. - Patients with uremia often have compromised nutritional status and may experience vitamin deficiencies, further contributing to pyridoxine depletion. *Diabetes mellitus* - **Diabetes mellitus** is a significant risk factor for INH-induced neuropathy because it is an independent cause of **peripheral neuropathy** itself, making patients more susceptible to additional nerve damage. - Diabetic patients may also have altered pyridoxine metabolism or suboptimal nutritional intake, predisposing them to INH toxicity. *Poor nutrition* - **Poor nutrition**, particularly malabsorption or inadequate dietary intake, directly contributes to **pyridoxine (vitamin B6) deficiency**. - Isoniazid's mechanism of neurotoxicity involves interfering with pyridoxine metabolism, so pre-existing deficiency significantly increases the risk of neuropathy.
Question 422: What is the best method for treating methanol poisoning?
- A. Calcium gluconate
- B. BAL
- C. Fomepizole (Correct Answer)
- D. Deferoxamine
Explanation: ***Fomepizole*** - **Fomepizole** (Antizol) is a potent inhibitor of **alcohol dehydrogenase**, the enzyme responsible for metabolizing methanol into toxic metabolites like formic acid [1]. - By inhibiting this enzyme, fomepizole prevents the formation of these harmful metabolites, thus halting the progression of methanol toxicity and reducing mortality [1]. - It is the **gold standard** antidote for methanol poisoning. *Calcium gluconate* - **Calcium gluconate** is primarily used to treat **hypocalcemia** and magnesium toxicity. - It has no role in the direct treatment or detoxification of methanol poisoning. *Deferoxamine* - **Deferoxamine** is a **chelating agent** used to treat **iron toxicity** by binding to iron and facilitating its excretion [3]. - It is not effective for methanol poisoning as it does not interact with methanol or its toxic metabolites. *BAL* - **BAL** (British Anti-Lewisite, dimercaprol) is a chelating agent primarily used for poisoning by **heavy metals** such as arsenic, mercury, and gold [2]. - It has no therapeutic role in methanol poisoning, which involves a different toxicological mechanism.
Question 423: Interstitial nephritis is associated with all of the following medications except:
- A. INH (Correct Answer)
- B. Diuretics
- C. Allopurinol
- D. Beta-lactam antibiotics
Explanation: ***INH*** - **Isoniazid (INH)** is primarily associated with **hepatotoxicity** (liver damage) and **peripheral neuropathy**, not typically interstitial nephritis. - While many drugs can rarely cause various adverse effects, INH is not a recognized common cause of **drug-induced interstitial nephritis**. *Beta-lactam antibiotics* - **Beta-lactam antibiotics**, including penicillins and cephalosporins, are among the most common causes of **drug-induced acute interstitial nephritis (AIN)**. - AIN is an **allergic hypersensitivity reaction** characterized by inflammation of the kidney's tubules and interstitium. *Diuretics* - Certain **diuretics**, particularly **thiazide diuretics** and **loop diuretics**, have been implicated in causing **acute interstitial nephritis**. - The mechanism is thought to be an **allergic or hypersensitivity reaction** within the renal tubules and interstitium. *Allopurinol* - **Allopurinol**, used to treat gout and hyperuricemia, is a known cause of **drug-induced acute interstitial nephritis**. - Renal involvement with allopurinol can range from mild tubular dysfunction to severe **acute kidney injury** due to AIN.
Question 424: What is the classification of Lorcaserin?
- A. Anti-anxiety
- B. Anti-smoking
- C. Anti-helminthic
- D. Anti-obesity (Correct Answer)
Explanation: ***Anti-obesity*** - Lorcaserin is a selective **serotonin 5-HT₂C receptor agonist** that works by promoting satiety and reducing food intake. - It is prescribed as a long-term treatment for **weight management** in adults who are obese or overweight with at least one weight-related comorbidity. *Anti-anxiety* - Anti-anxiety medications, such as **benzodiazepines** or **SSRIs**, primarily target neurotransmitters like GABA or serotonin 5-HT₁A receptors to reduce anxiety symptoms. - Lorcaserin's primary mechanism of action is distinct, focusing on the 5-HT₂C receptor for appetite regulation, not anxiety. *Anti-smoking* - Anti-smoking medications, like **varenicline** or **bupropion**, are designed to reduce nicotine cravings and withdrawal symptoms. - Their mechanisms often involve nicotinic acetylcholine receptors or dopamine and norepinephrine reuptake inhibition, which differs from lorcaserin's action. *Anti-helminthic* - Anti-helminthic drugs are used to treat **parasitic worm infections** by paralyzing or killing the worms. - Common examples include **albendazole** or **mebendazole**, which have no relation to appetite control or obesity treatment.
Question 425: What is the half-life of nicotine in blood?
- A. 2 hours (Correct Answer)
- B. 15 minutes
- C. 5 hours
- D. 24 hours
Explanation: ***2 hours*** - Nicotine has a **relatively short half-life** in the blood, typically around 2 hours, contributing to frequent dosing in tobacco users. - This rapid elimination means that nicotine concentrations decrease significantly within a few hours after the last dose, leading to **withdrawal symptoms** or cravings. *15 minutes* - A 15-minute half-life would imply an **extremely rapid clearance**, which is not characteristic of nicotine. - Such quick elimination would make it very difficult to maintain consistent drug levels and would lead to immediate, intense withdrawal. *5 hours* - While longer than the actual half-life, 5 hours is still within the realm of substances requiring **multiple daily doses**. - However, it would mean nicotine levels would remain elevated for a longer period than observed, potentially delaying withdrawal. *24 hours* - A 24-hour half-life would mean nicotine would accumulate significantly in the body with daily use, leading to **prolonged effects** and a much slower decline in concentrations after cessation. - This half-life is typical for drugs designed for **once-daily dosing**, which is not the case for nicotine.