NEET-PG 2015 Practice Questions

Q: Transport of lipids from the intestine to other tissues is by -

Chylomicrons. ***Chylomicrons*** - **Chylomicrons** are the **largest lipoprotein particles** that transport **dietary (exogenous) lipids** from the **intestine** to peripheral tissues - They are synthesized in **intestinal enterocytes** after fat absorption and enter the bloodstream via the **lymphatic system (thoracic duct)** - They carry **triglycerides (85-95%), cholesterol, phospholipids, and fat-soluble vitamins** (A, D, E, K) - **Apolipoprotein B-48** is the characteristic structural protein of chylomicrons - After delivering triglycerides to tissues (via lipoprotein lipase), chylomicron remnants are taken up by the **liver** *LDL (Low-Density Lipoprotein)* - LDL transports **cholesterol from the liver to peripheral tissues** (not from intestine) - It carries **endogenous cholesterol**, not dietary lipids from the intestine - Often called "**bad cholesterol**" due to its role in atherosclerosis - Contains **Apolipoprotein B-100** *HDL (High-Density Lipoprotein)* - HDL performs **reverse cholesterol transport** - moving excess cholesterol from peripheral tissues **back to the liver** - It does **not transport lipids from the intestine** to tissues - Called "**good cholesterol**" for its protective cardiovascular role - Contains **Apolipoprotein A-I and A-II** *VLDL (Very-Low-Density Lipoprotein)* - VLDL is synthesized in the **liver** (not intestine) and transports **endogenous triglycerides** to peripheral tissues - It carries lipids **from the liver**, not from the intestine - VLDL is converted to IDL and then LDL after losing triglycerides - Contains **Apolipoprotein B-100**

Q: Which method is used to separate a mixture of lipids?

Chromatography. ***Chromatography*** - **Chromatography** (e.g., thin-layer chromatography, gas chromatography, high-performance liquid chromatography) is widely used to separate lipids based on differences in their **polarity**, **molecular weight**, or **solubility** in various solvents. - This method allows for the isolation and identification of different lipid classes and individual lipid species from a complex mixture. *Electrophoresis* - **Electrophoresis** separates molecules based on their **charge** and **size** in an electric field, making it more commonly used for proteins and nucleic acids. - Lipids are generally **uncharged** or have very low charge, which makes them poorly suited for separation by standard electrophoretic methods without modification. *Isoelectric focusing* - **Isoelectric focusing** is a type of electrophoresis that separates molecules based on their **isoelectric point (pI)**, which is the pH at which a molecule has no net charge. - This technique is primarily used for **proteins** and **peptides**, as lipids typically lack ionizable groups necessary for establishing a distinct pI. *PAGE* - **PAGE** (Polyacrylamide Gel Electrophoresis) is a common method used to separate **proteins** and **nucleic acids** based on their size and charge. - Lipids are **hydrophobic** and do not readily migrate through an aqueous polyacrylamide gel matrix, making PAGE unsuitable for their direct separation.

Q: Bile acids are synthesized from ?

Cholesterol. ***Cholesterol*** - **Bile acids** are derivatives of **cholesterol**, synthesized in the liver through a multi-step enzymatic pathway. - The conversion of cholesterol to bile acids is a primary mechanism for the excretion and transport of cholesterol from the body. *Heme* - **Heme** is a component of hemoglobin and myoglobin, primarily involved in oxygen transport and storage. - Its degradation product is **bilirubin**, which forms part of bile but is distinct from bile acids. *Ribulose* - **Ribulose** is a 5-carbon sugar, playing a key role in the **pentose phosphate pathway** and the **Calvin cycle** in photosynthesis. - It is not a precursor for bile acid synthesis. *Arachidonic acid* - **Arachidonic acid** is a polyunsaturated fatty acid that serves as a precursor for **eicosanoids** (prostaglandins, thromboxanes, and leukotrienes). - These molecules are involved in inflammation and immune responses but are unrelated to bile acid synthesis.

Q: Most abundant source of fuel in starvation -

Adipose tissue. ***Adipose tissue*** - **Adipose tissue** stores **triglycerides**, which are hydrolyzed into fatty acids and glycerol to serve as the body's primary energy source during prolonged starvation. - The energy reserve in adipose tissue is significantly larger than glycogen stores, providing **sustained fuel** for days or weeks. *Liver glycogen* - **Liver glycogen** is a readily available source of glucose but is rapidly depleted within **12-24 hours** during starvation. - Its primary role is to maintain **blood glucose levels** for glucose-dependent tissues like the brain. *Muscle glycogen* - **Muscle glycogen** is used primarily for **muscle contraction** and cannot be directly released into the bloodstream to maintain blood glucose levels. - While it's a significant energy reserve for working muscles, it does not contribute to systemic fuel needs during starvation. *Blood glucose* - **Blood glucose** is the immediate circulating fuel, but it is tightly regulated and its levels decrease during starvation as glycogen stores are depleted. - It is not an abundant stored source of fuel but rather a transport form of energy.

Q: Which of the following drug combinations demonstrates receptor level antagonism?

Isoprenaline (agonist) and Propranolol (antagonist). ***Isoprenaline (agonist) and Propranolol (antagonist)*** - **Propranolol** is a **beta-adrenergic receptor antagonist**, meaning it binds to and blocks beta-adrenergic receptors. - **Isoprenaline** is a **beta-adrenergic receptor agonist**, meaning it activates these same receptors. Their combined action demonstrates **receptor-level antagonism** as propranolol prevents isoprenaline from binding and eliciting its effect. *Histamine and Adrenaline* - This combination illustrates **physiological antagonism**, where two drugs produce opposite effects through different mechanisms and different receptors. - **Adrenaline** causes bronchodilation and vasoconstriction via adrenergic receptors, counteracting the effects of **histamine** (e.g., bronchoconstriction, vasodilation) which acts on histamine receptors. *Adrenaline and Isoprenaline* - Both **adrenaline** and **isoprenaline** are **agonists** of adrenergic receptors, specifically beta-adrenergic receptors. - They would produce similar effects (e.g., increased heart rate, bronchodilation) rather than opposing each other at the receptor level. *None of the options* - This is incorrect because **Isoprenaline and Propranolol** is a valid example of receptor-level antagonism, making this option unnecessary.

Q: Fastest receptor mediated action is through?

Intrinsic ion channels. ***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.

Q: Which ACE inhibitor is safe in renal failure?

Benazepril. ***Benazepril*** - Among the listed ACE inhibitors, benazepril has the **most favorable excretion profile** in renal failure with approximately **50% renal and 50% hepatic elimination** (dual excretion pathway). - This balanced elimination reduces the risk of drug accumulation compared to predominantly renally excreted ACE inhibitors. - While dose adjustment may still be needed in **severe renal impairment**, benazepril is considered the **safest option among those listed** for patients with renal dysfunction. - **Note:** Fosinopril (not listed here) has true 50/50 dual elimination and requires no dose adjustment in renal failure, making it the ideal choice in clinical practice. *Captopril* - This ACE inhibitor undergoes predominantly **renal excretion (95%)** as unchanged drug and metabolites. - Requires significant **dose reduction** in renal failure to prevent accumulation and adverse effects including **hyperkalemia** and **hypotension**. - Less safe than benazepril in renal impairment due to heavy dependence on renal elimination. *Enalapril* - Enalapril is a prodrug converted to **enalaprilat**, with approximately **90% renal excretion**. - Dose adjustment is mandatory based on **creatinine clearance** in patients with renal failure. - Higher risk of accumulation and toxicity compared to dual-elimination ACE inhibitors like benazepril.

Q: At which receptor is the primary action of antipsychotic medications required?

D2 dopaminergic. ***D2 dopaminergic*** - The **antipsychotic effects** of typical (first-generation) antipsychotics are primarily mediated through **D2 receptor blockade** [1]. - Blocking D2 receptors in the **mesolimbic pathway** helps reduce positive symptoms of psychosis like hallucinations and delusions [2]. *M, muscarinic* - **Muscarinic receptor blockade** is a common adverse effect of some antipsychotics, leading to anticholinergic side effects such as **dry mouth** and **blurred vision**, rather than their primary therapeutic action. - This action does not directly contribute to the antipsychotic effect. *D1 dopaminergic* - While D1 receptors are involved in dopamine signaling, they are **not the primary target** for the antipsychotic action of most drugs [1]. - Some atypical antipsychotics may affect D1 receptors, but it's secondary to their D2 antagonism and serotonin modulation. *5HT4 serotonergic* - **Serotonin receptors (5HT)**, particularly 5HT2A, are important targets for atypical (second-generation) antipsychotics. - However, 5HT4 receptors are **not a primary target** for the antipsychotic effects, and 5HT2A blockade modulates dopamine release, which is still connected to the D2 hypothesis.

Q: Which of the following is non-selective 3rd generation Beta blocker ?

Carvedilol. ***Carvedilol*** - **Carvedilol** is a **non-selective beta-adrenergic antagonist** (blocks both β1 and β2 receptors) with **additional α1-adrenergic blocking activity**, making it a true **3rd generation beta-blocker**. - The α1-blockade provides **vasodilatory properties**, reducing peripheral vascular resistance and improving hemodynamics. - It has favorable effects on lipid metabolism and insulin sensitivity, making it particularly useful in heart failure and hypertension. - Its non-selective beta-blockade combined with vasodilation distinguishes it from selective 3rd generation agents. *Betaxolol* - **Betaxolol** is a **selective β1-adrenergic antagonist** without vasodilatory properties. - Classified as a **2nd generation beta-blocker** due to its cardioselectivity. - Primarily used in glaucoma and hypertension but lacks the non-selective profile and additional mechanisms of 3rd generation agents. *Celiprolol* - **Celiprolol** is a **β1-selective antagonist** with **β2-agonistic effects** providing vasodilation. - While classified as 3rd generation due to vasodilatory properties, it is **selective for β1**, not non-selective. - Its β2-agonism causes peripheral vasodilation but maintains β1-selectivity. *Nebivolol* - **Nebivolol** is a highly **selective β1-adrenergic antagonist** with **vasodilatory effects via nitric oxide (NO) release**. - Classified as 3rd generation due to NO-mediated vasodilation, but it is **β1-selective**, not non-selective. - The combination of high β1-selectivity and endothelial-mediated vasodilation makes it unique among 3rd generation agents.

Q: Beta-blockers should be used with caution in patients with?

Conduction defect. ***Conduction defect*** - Beta-blockers **slow heart rate** and **decrease AV nodal conduction**, which can worsen pre-existing conduction defects like **AV block** or **sick sinus syndrome**. - Their use can lead to **symptomatic bradycardia** or complete heart block in susceptible individuals. - This represents a **strong relative contraindication** requiring significant caution. *Hypertension* - Beta-blockers are a **first-line treatment for hypertension**, effectively lowering blood pressure by reducing cardiac output and renin release. - They are generally **well-tolerated** and beneficial in most hypertensive patients. *Glaucoma* - Topical beta-blockers, such as **timolol**, are a common treatment for open-angle glaucoma as they **reduce aqueous humor production**, thereby lowering intraocular pressure. - Systemic use of beta-blockers does not typically worsen glaucoma and may even offer some benefit. *CHF* - While certain beta-blockers (**carvedilol, metoprolol succinate, bisoprolol**) are now proven beneficial in **chronic heart failure with reduced ejection fraction (HFrEF)**, they do require careful use. - They must be **initiated at low doses and carefully titrated** to avoid acute decompensation, and are **contraindicated in acute decompensated heart failure**. - However, **conduction defects** represent a **stronger contraindication** where beta-blockers can cause life-threatening bradycardia or complete heart block, making it the best answer for conditions requiring the most caution.

Question 1

Transport of lipids from the intestine to other tissues is by -

Accepted Answer

Chylomicrons

Answer

LDL

Answer

HDL

Answer

VLDL

Question 2

Which method is used to separate a mixture of lipids?

Accepted Answer

Chromatography

Answer

Electrophoresis

Answer

Isoelectric focusing

Answer

PAGE

Question 3

Bile acids are synthesized from ?

Accepted Answer

Cholesterol

Answer

Heme

Answer

Ribulose

Answer

Arachidonic acid

Question 4

Most abundant source of fuel in starvation -

Accepted Answer

Adipose tissue

Answer

Liver glycogen

Answer

Muscle glycogen

Answer

Blood glucose

Question 5

Which of the following drug combinations demonstrates receptor level antagonism?

Accepted Answer

Isoprenaline (agonist) and Propranolol (antagonist)

Answer

Histamine and Adrenaline

Answer

Adrenaline and Isoprenaline

Answer

None of the options

Question 6

Fastest receptor mediated action is through?

Accepted Answer

Intrinsic ion channels

Answer

Intracellular receptors

Answer

Cell surface receptors

Answer

Receptor tyrosine kinases

Question 7

Which ACE inhibitor is safe in renal failure?

Accepted Answer

Benazepril

Answer

Captopril

Answer

Enalapril

Answer

None of the options

Question 8

At which receptor is the primary action of antipsychotic medications required?

Accepted Answer

D2 dopaminergic

Answer

M, muscarinic

Answer

5HT4 serotonergic

Answer

D1 dopaminergic

Question 9

Which of the following is non-selective 3rd generation Beta blocker ?

Accepted Answer

Carvedilol

Answer

Betaxolol

Answer

Celiprolol

Answer

Nebivolol

Question 10

Beta-blockers should be used with caution in patients with?

Accepted Answer

Conduction defect

Answer

Hypertension

Answer

CHF

Answer

Glaucoma

NEET-PG 2015

Biochemistry

Pharmacology