Biochemistry
1 questionsWhat is the number of variable regions present on each light and heavy chain of an antibody?
NEET-PG 2013 - Biochemistry NEET-PG Practice Questions and MCQs
Question 571: What is the number of variable regions present on each light and heavy chain of an antibody?
- A. 1 (Correct Answer)
- B. 2
- C. 3
- D. 4
Explanation: ***1*** - Each **light chain** and **heavy chain** within an antibody molecule contains **one variable region (V domain)**. - These variable regions are crucial for **antigen binding specificity**, as they combine to form the antigen-binding site. - The variable domain is located at the **N-terminal end** of each chain. *2* - While a complete antibody molecule has **two antigen-binding sites** (bivalent), each formed by pairing of VH and VL domains, individual chains possess only **one variable region each**. - The number '2' refers to the total number of identical binding sites on the intact antibody, not the number of variable regions per chain. *3* - The number **3** does not correspond to the number of variable regions on individual chains. - This might be confused with the **three complementarity-determining regions (CDRs)** present within each variable domain (CDR1, CDR2, CDR3), which are hypervariable loops that directly contact the antigen. *4* - The number **4** is incorrect for variable regions. - This number corresponds to the total number of **polypeptide chains** in a complete IgG antibody (2 heavy + 2 light chains), or the number of **constant domains** in some heavy chain isotypes (IgM, IgE have 4 CH domains).
Internal Medicine
2 questionsWhich of the following is true about Hepatitis A virus?
What is the drug of choice for bleeding oesophageal varices?
NEET-PG 2013 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 571: Which of the following is true about Hepatitis A virus?
- A. Causes chronic hepatitis
- B. Helps HDV replication
- C. Causes cirrhosis
- D. Common cause of hepatitis in children (Correct Answer)
Explanation: ***Common cause of hepatitis in children*** - **Hepatitis A virus (HAV)** infection is often acquired in childhood, particularly in areas with poor sanitation, and many infections are **asymptomatic** or mild in children [1]. - Due to their developing immune systems and often exposure in daycare or school settings, children are a highly susceptible population for HAV transmission [1]. *Causes cirrhosis* - **HAV infection** is an **acute self-limiting illness** and typically does not lead to chronic liver disease or cirrhosis [1]. - **Cirrhosis** is primarily associated with chronic viral hepatitis (e.g., HBV, HCV), alcohol-related liver disease, or certain autoimmune conditions. *Helps HDV replication* - **Hepatitis D virus (HDV)** is a **defective virus** that requires the presence of **Hepatitis B virus (HBV)** surface antigen (HBsAg) for its replication and assembly [1]. - **HAV** has no role in the replication or pathogenesis of **HDV** [1]. *Causes chronic hepatitis* - **HAV infection** results in an **acute inflammatory response** in the liver that resolves spontaneously in most cases [1]. - Unlike **HBV** and **HCV**, **HAV** does not establish a persistent infection and, therefore, does not cause chronic hepatitis [1].
Question 572: What is the drug of choice for bleeding oesophageal varices?
- A. Ethanolamine oleate
- B. Octreotide (Correct Answer)
- C. Propanolol
- D. Phytonadione
Explanation: ***Octreotide*** - **Octreotide** is an analogue of **somatostatin** that reduces splanchnic blood flow and portal pressure, thereby decreasing bleeding from esophageal varices. - It is often used in the acute management of **bleeding esophageal varices** due to its rapid onset of action and favorable safety profile. *Ethanolamine oleate* - **Ethanolamine oleate** is a **sclerosing agent** used for endoscopic sclerotherapy of esophageal varices, not typically as the initial drug of choice for acute bleeding [1]. - It acts by causing inflammation and fibrosis of the varices, which can be effective but carries risks such as **esophageal ulceration** or perforation. *Propranolol* - **Propranolol** is a **non-selective beta-blocker** used for the prophylactic prevention of variceal bleeding, not for acute management of active bleeding. - It works by reducing portal venous pressure by decreasing cardiac output and splanchnic vasoconstriction. *Phytonadione* - **Phytonadione** (vitamin K1) is used to reverse **coumarin anticoagulant effects** or to treat **vitamin K deficiency**, which can contribute to bleeding but is not a direct treatment for variceal bleeding itself. - It helps in the synthesis of **coagulation factors II, VII, IX, and X**, thereby improving clotting.
Microbiology
3 questionsWhich gene of the hepatitis B virus has the longest coding sequence?
Prions are best killed by
What is the primary use of the Hybridoma technique?
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 571: Which gene of the hepatitis B virus has the longest coding sequence?
- A. P gene (Correct Answer)
- B. X gene
- C. S gene
- D. C gene
Explanation: ***P gene*** - The **P gene** (polymerase gene) encodes the viral **reverse transcriptase**, which is crucial for replicating the HBV genome. - This enzyme is very large and complex, requiring the **longest coding sequence** to accommodate all its functional domains. *X gene* - The **X gene** encodes the **HBx protein**, which is a transcriptional transactivator and plays a role in hepatocarcinogenesis. - It has a relatively **short coding sequence** compared to the P gene. *S gene* - The **S gene** encodes the **surface antigens (HBsAg)**, which are involved in viral entry and immune evasion. - It has a **shorter coding sequence** than the P gene, as it primarily codes for structural proteins. *C gene* - The **C gene** encodes the **core protein (HBcAg)**, which forms the viral nucleocapsid, and the **HBeAg**. - Its coding sequence is also **shorter** than that of the P gene, reflecting its role in structural and regulatory functions.
Question 572: Prions are best killed by
- A. Incineration at high temperatures
- B. Autoclaving at 134°C (for 18 minutes) (Correct Answer)
- C. 5% formalin solution
- D. Sodium hypochlorite solution
Explanation: ***Autoclaving at 134°C (for 18 minutes)*** - **Prions** are highly resistant to conventional sterilization methods, and **autoclaving at 134°C for at least 18 minutes** is the **most effective method for sterilizing reusable medical instruments** contaminated with prions. - This high temperature and pressure protocol (WHO/CDC recommended) helps to denature the misfolded protein structure of prions, reducing their infectivity to safe levels. - **In the context of sterilization and disinfection**, this is the best practical method for surgical instruments that cannot be discarded. *Incineration at high temperatures* - **Incineration at 800-1000°C** achieves complete combustion and is **highly effective** at destroying prions. - However, incineration is used only for **single-use disposable items** and prion-contaminated waste, not for reusable surgical instruments. - In the clinical context of sterilization (implied by this topic), autoclaving is the preferred answer as it applies to reusable equipment. *Sodium hypochlorite solution* - **Sodium hypochlorite** (bleach) at **high concentrations** (20,000 ppm or 2% available chlorine) for extended contact times (1+ hours) can inactivate prions. - However, it is **corrosive to instruments**, damages tissue samples, and requires precise concentration and exposure conditions, making it less practical than autoclaving. *5% formalin solution* - Formalin is **not effective at inactivating prions**; it can actually **preserve and stabilize** prion infectivity. - Formalin cross-links proteins and preserves tissue morphology but does not reliably break down the highly stable **beta-sheet structures** characteristic of prions.
Question 573: What is the primary use of the Hybridoma technique?
- A. Monoclonal antibodies (Correct Answer)
- B. Antigen
- C. Specific antibodies
- D. Cytokines
Explanation: ***Monoclonal antibodies*** - The **hybridoma technique** is primarily used to produce **monoclonal antibodies (MAbs)**, which are highly specific antibodies derived from a single B-cell clone. - These antibodies recognize a **single epitope** on an antigen, providing exceptional specificity and uniformity. - The technique involves **fusing a B-lymphocyte** (antibody-producing cell) with a **myeloma cell** (immortal cancer cell) to create a hybridoma that continuously produces identical antibodies. - This is the **gold standard** for producing large quantities of identical, highly specific antibodies for diagnostic and therapeutic use. *Specific antibodies* - While monoclonal antibodies are indeed specific, this term is **too vague** and could refer to any antibody with specificity, including polyclonal antibodies. - **Polyclonal antibodies** are also specific but are produced through conventional immunization, not the hybridoma technique. - The defining characteristic of the hybridoma technique is that it produces **monoclonal** (single clone) antibodies, not just "specific" ones. *Antigen* - An **antigen** is a molecule that elicits an immune response and is used to immunize animals during antibody production. - However, antigens are the **input** for antibody production, not the **product** of the hybridoma technique. *Cytokines* - **Cytokines** are signaling molecules involved in immune cell communication and regulation. - They are not produced by the hybridoma technique, which is specifically designed for **antibody production**.
Pharmacology
4 questionsWhich of the following is a parenteral direct thrombin inhibitor?
Which of the following statements about clofazimine is incorrect?
All of the following are adverse effects of nicotinic acid except:
Which drug is commonly used to treat chronic hepatitis B infection?
NEET-PG 2013 - Pharmacology NEET-PG Practice Questions and MCQs
Question 571: Which of the following is a parenteral direct thrombin inhibitor?
- A. Ximelagatran
- B. Dabigatran
- C. Argatroban (Correct Answer)
- D. Heparin
Explanation: ***Argatroban*** - **Argatroban** is a **synthetic direct thrombin inhibitor** administered exclusively via **intravenous infusion**, making it a parenteral drug. - It does not require antithrombin for its action and is primarily used in patients with **heparin-induced thrombocytopenia (HIT)**. *Ximelagatran* - **Ximelagatran** was an **oral direct thrombin inhibitor** but was withdrawn from the market due to concerns about severe **liver toxicity**. - As an oral drug, it is not a parenteral medication. *Dabigatran* - **Dabigatran** is a **direct thrombin inhibitor** that is administered **orally** in capsule form (as dabigatran etexilate, a prodrug). - Therefore, it is not a parenteral medication. *Heparin* - **Heparin** is an **indirect thrombin inhibitor** because it requires binding to **antithrombin** to exert its anticoagulant effect. - Although administered parenterally, its mechanism of action is indirect.
Question 572: Which of the following statements about clofazimine is incorrect?
- A. Does not interfere with DNA synthesis (Correct Answer)
- B. Used in lepra reaction
- C. Used in treatment of leprosy
- D. Causes ichthyosis and hyperpigmentation
Explanation: ***Does not interfere with DNA synthesis*** - Clofazimine's primary mechanism of action involves **DNA binding** and **interference with bacterial DNA synthesis**. - It also generates **reactive oxygen species** and disrupts membrane function, contributing to its bactericidal effect. - **This statement is INCORRECT** - clofazimine does interfere with DNA synthesis. *Used in lepra reaction* - Clofazimine is a crucial component in the treatment of **leprosy**, particularly effective in managing **Type 2 lepra reactions (erythema nodosum leprosum)** due to its anti-inflammatory effects. - It helps to reduce the severity and duration of these acute inflammatory episodes. *Used in treatment of leprosy* - Clofazimine is a **core component of multidrug therapy (MDT) for leprosy**, particularly in multibacillary leprosy. - It is recommended by the **WHO** as part of the standard treatment regimen for leprosy. *Causes ichthyosis and hyperpigmentation* - Clofazimine commonly causes **hyperpigmentation of the skin, conjunctiva, and bodily fluids**, often appearing reddish-brown to black. - Less commonly, it can also lead to **ichthyosis (dry, scaly skin)** as a side effect.
Question 573: All of the following are adverse effects of nicotinic acid except:
- A. Liver dysfunction
- B. Vasodilation
- C. Hyperpigmentation
- D. Pancreatitis (Correct Answer)
Explanation: ***Pancreatitis*** - **Pancreatitis** is not a commonly reported adverse effect of nicotinic acid (niacin) therapy. - While other gastrointestinal side effects like nausea and vomiting can occur, pancreatic inflammation is not characteristic. *Vasodilation* - **Cutaneous flushing** and **vasodilation** are very common adverse effects of nicotinic acid, mediated by prostaglandin release. - This effect can cause a sensation of warmth, redness, and itching, especially at the start of therapy. *Liver dysfunction* - **Liver dysfunction**, including elevated liver enzymes and rare cases of **hepatotoxicity**, can occur with high doses of nicotinic acid. - Regular monitoring of liver function tests is recommended for patients on niacin therapy. *Hyperpigmentation* - **Hyperpigmentation**, particularly **acanthosis nigricans**, is a known cutaneous side effect of nicotinic acid. - This typically presents as dark, velvety patches on the skin, especially in skin fold areas.
Question 574: Which drug is commonly used to treat chronic hepatitis B infection?
- A. Zanamivir
- B. Atazanavir
- C. Abacavir
- D. Entecavir (Correct Answer)
Explanation: ***Entecavir*** - **Entecavir** is an oral **nucleoside analog reverse transcriptase inhibitor** specifically approved and widely used for the treatment of **chronic hepatitis B virus (HBV) infection**. - It works by inhibiting HBV DNA polymerase, thereby reducing **viral replication** and preventing disease progression. *Atazanavir* - **Atazanavir** is a **protease inhibitor** primarily used in the treatment of **HIV infection**. - It is not indicated for the treatment of **hepatitis B virus infection**. *Zanamivir* - **Zanamivir** is a **neuraminidase inhibitor** used in the treatment and prevention of **influenza A and B viruses**. - It has no activity against **hepatitis B virus**. *Abacavir* - **Abacavir** is a **nucleoside reverse transcriptase inhibitor (NRTI)** used to treat **HIV infection**. - While it is an NRTI, it does not have significant efficacy against **hepatitis B virus** and is not used for its treatment.