Biochemistry
4 questionsWhat are Okazaki fragments?
What is the primary role of calnexin and calreticulin in the endoplasmic reticulum?
Which gene is responsible for the production of COX type 3?
What is a key similarity between the processes of replication and transcription?
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 451: What are Okazaki fragments?
- A. Long pieces of DNA on the lagging strand.
- B. Short pieces of DNA on the lagging strand. (Correct Answer)
- C. Short pieces of DNA on the leading strand.
- D. Long pieces of DNA on the leading strand.
Explanation: ***Short pieces of DNA on the lagging strand.*** - **Okazaki fragments** are the short, newly synthesized DNA fragments that are formed on the **lagging strand** during DNA replication. - The lagging strand is synthesized discontinuously because DNA polymerase can only add nucleotides in the **5' to 3' direction**, requiring it to move away from the replication fork as the DNA unwinds. *Long pieces of DNA on the lagging strand.* - The lagging strand is synthesized discontinuously in **short fragments**, not long continuous pieces. - The enzyme **DNA ligase** eventually joins these short fragments together to form a continuous strand. *Short pieces of DNA on the leading strand.* - The **leading strand** is synthesized continuously in one long stretch, moving towards the replication fork. - It does not require the synthesis of short fragments like the lagging strand. *Long pieces of DNA on the leading strand.* - While the leading strand is synthesized in a continuous, long piece, this statement does not accurately describe Okazaki fragments, which are specific to the lagging strand. - The leading strand's continuous synthesis is due to its **3' to 5' template orientation**, allowing DNA polymerase to proceed uninterrupted.
Question 452: What is the primary role of calnexin and calreticulin in the endoplasmic reticulum?
- A. Degrade misfolded proteins
- B. Act as chaperones (Correct Answer)
- C. Serve as tumor markers
- D. Facilitate enzymatic reactions
Explanation: ***Act as chaperones*** - **Calnexin** and **calreticulin** are **chaperone proteins** located in the **endoplasmic reticulum (ER)**. - They bind to unfolded or misfolded glycoproteins to assist in their proper folding and assembly. - They are part of the **ER quality control system**, ensuring only properly folded proteins proceed to the Golgi apparatus. *Degrade misfolded proteins* - While misfolded proteins are eventually degraded through **ER-associated degradation (ERAD)**, this is not the primary function of calnexin and calreticulin. - These chaperones first attempt to **rescue and refold** proteins; degradation is a separate process involving other machinery. *Serve as tumor markers* - **Calnexin** and **calreticulin** are not typically used as **tumor markers** in clinical practice. - Their functions are related to protein quality control within the cell, not cancer detection. *Facilitate enzymatic reactions* - While some proteins in the ER are enzymes, **calnexin** and **calreticulin** themselves are not enzymes, nor do they primarily facilitate enzymatic reactions. - Their function is to ensure correct protein folding, distinct from direct catalytic activity.
Question 453: Which gene is responsible for the production of COX type 3?
- A. COX 3 gene
- B. COX 2 gene
- C. None of the above
- D. COX I gene (Correct Answer)
Explanation: ***COX I gene*** - COX-3 is an **alternatively spliced variant** of the **COX-1 gene** (specifically, a splice variant of the COX-1 mRNA that retains intron 1). - While it was initially thought to be a distinct gene, research has shown that it arises from the same genetic locus as COX-1. *COX 2 gene* - The COX-2 gene encodes for the **inducible cyclooxygenase enzyme**, which is responsible for prostaglandin synthesis during inflammation. - It is a separate gene from COX-1 and has distinct regulatory mechanisms and physiological roles. *COX 3 gene* - There is currently **no distinct gene in humans** specifically identified as "COX-3". - COX-3 refers to a protein isoform derived from the COX-1 gene, not a separate genetic locus. *None of the above* - This option is incorrect because COX-3 is indeed derived from the **COX-1 gene** through alternative splicing. - The existence of COX-3 as a distinct protein product has been demonstrated, although its precise physiological role in humans is still under investigation.
Question 454: What is a key similarity between the processes of replication and transcription?
- A. Use RNA primers for initiation.
- B. Use ribonucleotides as precursors.
- C. Are semi-conservative events.
- D. Involve phosphodiester bond formation with elongation occurring in the 5' - 3' direction. (Correct Answer)
Explanation: ***Involve phosphodiester bond formation with elongation occurring in the 5' - 3' direction.*** - Both DNA replication and RNA transcription synthesize nucleic acid polymers by forming **phosphodiester bonds** between incoming nucleotides. - The new strand in both processes is always elongated in the **5' to 3' direction**, as new nucleotides are added to the 3' hydroxyl group of the growing strand. *Use RNA primers for initiation.* - **DNA replication** requires **RNA primers** to initiate synthesis of new DNA strands, as DNA polymerase cannot start a new strand *de novo*. - **Transcription (RNA synthesis)** does not require a primer; **RNA polymerase** can initiate transcription *de novo* at a promoter sequence. *Use ribonucleotides as precursors.* - **Transcription** uses **ribonucleotides** (ATP, UTP, CTP, GTP) as precursors to synthesize RNA. - **Replication** primarily uses **deoxyribonucleotides** (dATP, dTTP, dCTP, dGTP) to synthesize DNA, although it temporarily uses ribonucleotides for RNA primers. *Are semi-conservative events.* - **DNA replication** is a **semi-conservative process**, meaning each new DNA molecule consists of one original strand and one newly synthesized strand. - **Transcription** is **not semi-conservative**; it involves synthesizing an RNA molecule from a DNA template, leaving the original DNA template unchanged.
Internal Medicine
1 questionsIn which condition is the Doll's Eye Reflex tested?
NEET-PG 2015 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 451: In which condition is the Doll's Eye Reflex tested?
- A. Hemiplegic
- B. Paraplegic
- C. Cerebral palsy
- D. Unconscious patients (Correct Answer)
Explanation: ***Unconscious patients*** - The **Doll's Eye Reflex**, also known as the **oculocephalic reflex**, is a brainstem reflex used to assess brainstem function in **comatose or unconscious patients** [1]. - It is positive if the eyes move in the opposite direction to the head turn, indicating intact brainstem pathways [1]. *Hemiplegic* - **Hemiplegia** refers to paralysis on one side of the body, often due to stroke or brain injury. - While it can be associated with altered consciousness, the Doll's Eye Reflex specifically tests brainstem integrity in unconscious states, not the motor deficits of hemiplegia itself. *Paraplegic* - **Paraplegia** is paralysis affecting the lower half of the body. - This condition primarily involves spinal cord damage and does not directly relate to the assessment of brainstem function using the Doll's Eye Reflex. *Cerebral palsy* - **Cerebral palsy** is a group of disorders affecting movement, muscle tone, or posture, caused by damage to the developing brain. - While individuals with cerebral palsy may have neurological impairments, the Doll's Eye Reflex is not a primary diagnostic or assessment tool for this chronic condition; it is used acutely in unconscious states.
Pathology
2 questionsFibrosis associated with liver cirrhosis is mediated by -
Which of the following markers is specific for gastro-intestinal stromal tumor (GIST)?
NEET-PG 2015 - Pathology NEET-PG Practice Questions and MCQs
Question 451: Fibrosis associated with liver cirrhosis is mediated by -
- A. Platelet-Derived Growth Factor (PDGF)
- B. Transforming Growth Factor-beta (TGF-β) (Correct Answer)
- C. Vascular Endothelial Growth Factor (VEGF)
- D. Tumor Necrosis Factor-alpha (TNF-α)
Explanation: ***PDGF*** - Platelet-Derived Growth Factor (**PDGF**) is a critical mediator in the **fibrogenic response** associated with liver cirrhosis [1]. - It stimulates the **proliferation** and activation of hepatic stellate cells, leading to excessive **collagen deposition** and fibrosis [1][2]. *ICAM-1* - Intercellular Adhesion Molecule-1 (**ICAM-1**) primarily mediates **cell adhesion** and is involved in inflammatory processes, not directly in fibrosis. - While it may play a role in **leukocyte recruitment**, it does not contribute significantly to the fibrogenic pathway in liver cirrhosis. *PcAM-l* - **PCAM-1** (Platelet/endothelial cell adhesion molecule-1) is involved in **cell adhesion** and is primarily expressed on endothelial cells. - Its role is more associated with **angiogenesis** and inflammation, lacking direct involvement in the fibrogenic process of cirrhosis. *IFN-y* - Interferon-gamma (**IFN-y**) is a cytokine that predominantly has a role in **immune modulation** and does not directly induce fibroblast activation. - It may have regulatory effects on inflammation but does not lead to significant fibrosis associated with liver cirrhosis. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 31-32. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 830-832.
Question 452: Which of the following markers is specific for gastro-intestinal stromal tumor (GIST)?
- A. CD117 (Correct Answer)
- B. CD34
- C. CD23
- D. S-100
Explanation: ***CD 117*** - CD 117 (c-KIT) is the **primary marker** for gastrointestinal stromal tumors (GIST), indicating the presence of the **c-KIT gene mutation** [1]. - Its expression is crucial for diagnosing GISTs, as it is found in nearly all cases of these tumors. *CD 34* - While CD 34 is expressed in some GISTs, it is a **more general marker** associated with stem cells and not specific for GISTs. - GISTs can be negative for CD 34, making it unsuitable for definitive diagnosis. *S-100* - S-100 is typically a marker for **melanocytes** and neuroectodermal tumors, not for GISTs. - It is often used to identify **schwannomas** or **melanomas**, which are unrelated to GIST pathology. *CD 23* - CD 23 is primarily a marker for **chronic lymphocytic leukemia (CLL)** and some forms of lymphoma, not associated with GISTs. - Its presence indicates **lymphoid** lineage, further diverging from GISTs, which are **mesenchymal tumors**. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Gastrointestinal Tract, pp. 782-783.
Pharmacology
1 questionsWhich statement best describes first-order kinetics in pharmacokinetics?
NEET-PG 2015 - Pharmacology NEET-PG Practice Questions and MCQs
Question 451: Which statement best describes first-order kinetics in pharmacokinetics?
- A. Absorption of the drug is independent of the serum concentration
- B. Elimination of the drug is proportional to the serum concentration (Correct Answer)
- C. Absorption of the drug is proportional to the serum concentration
- D. Elimination of the drug is independent of the serum concentration
Explanation: ***Elimination of the drug is proportional to the serum concentration*** - In **first-order kinetics**, a **constant fraction** (or percentage) of the drug is eliminated per unit of time. - This means that as the **serum drug concentration** increases, the absolute amount of drug eliminated per unit time also increases proportionally. *Absorption of the drug is independent of the serum concentration* - Drug absorption is generally driven by factors like **concentration gradient**, surface area, and blood flow, and while it can be influenced by drug concentration, this statement does not define first-order kinetics of *elimination*. - This statement is not the primary characteristic distinguishing first-order from zero-order kinetics regarding drug disposition. *Elimination of the drug is independent of the serum concentration.* - This describes **zero-order kinetics**, where a **constant amount** of drug is eliminated per unit of time, regardless of the serum concentration. - In zero-order kinetics, the elimination rate becomes saturated, so the elimination process cannot keep up with higher drug concentrations. *Absorption of the drug is proportional to the serum concentration* - While drug absorption can be proportional to the concentration (especially through passive diffusion), first-order kinetics specifically refers to the **elimination phase** of pharmacokinetics. - The rate of absorption can be a complex process and is not the defining characteristic for distinguishing first-order from zero-order *elimination*.
Physiology
1 questionsWhich of the following is a potassium Channelopathy?
NEET-PG 2015 - Physiology NEET-PG Practice Questions and MCQs
Question 451: Which of the following is a potassium Channelopathy?
- A. Hyperkalemic periodic paralysis
- B. Long QT-syndrome
- C. Episodic ataxia I (Correct Answer)
- D. Hypokalemic periodic paralysis
Explanation: ***Episodic ataxia I*** - This condition is caused by mutations in the **KCNA1 gene**, which encodes the **Kv1.1 voltage-gated potassium channel**. - It represents a **classic neuromuscular potassium channelopathy** with episodes of **ataxia**, **dysarthria**, and myokymia. - This is a pure potassium channelopathy affecting the nervous system. *Hyperkalemic periodic paralysis* - This condition is caused by mutations in the **SCN4A gene**, which encodes a **sodium channel** subunit in skeletal muscle. - Despite the name suggesting potassium involvement, it is a **sodium channelopathy**, not a potassium channelopathy. - Episodes are triggered by elevated serum potassium levels. *Long QT syndrome* - Several subtypes (LQT1, LQT2, LQT5) are indeed caused by mutations in **potassium channel genes** (KCNQ1, KCNH2, KCNE1). - However, Long QT syndrome is a **heterogeneous group** that also includes sodium (LQT3) and calcium channelopathies. - It is classified as a **cardiac channelopathy** affecting ventricular repolarization. - In the context of this question, **Episodic ataxia I** is the most specific example of a pure potassium channelopathy. *Hypokalemic periodic paralysis* - This condition is most commonly caused by mutations in the **CACNA1S gene** (encoding a **calcium channel**) or **SCN4A gene** (encoding a **sodium channel**). - It is not a potassium channelopathy despite the hypokalemia that triggers episodes.
Surgery
1 questionsSolution currently used for liver preservation for transplantation is?
NEET-PG 2015 - Surgery NEET-PG Practice Questions and MCQs
Question 451: Solution currently used for liver preservation for transplantation is?
- A. IGL-1 solution
- B. Ross Marshall Citrate solution
- C. University of Wisconsin (UW) solution (Correct Answer)
- D. Kyoto ET solution
Explanation: ***University of Wisconsin (UW) solution*** - The **University of Wisconsin (UW) solution** is widely considered the gold standard for **organ preservation**, particularly for liver transplantation, due to its superior ability to extend cold ischemia time. - It contains a unique blend of components, including **lactobionate, raffinose, and hydroxyethyl starch**, which help to minimize cellular swelling, prevent free radical injury, and maintain cellular integrity during cold storage. *IGL-1 solution* - **IGL-1** is a more recent preservation solution designed to be used with **machine perfusion** systems. - While showing promise, it is **not yet as universally adopted** as UW solution for static cold storage of livers. *Ross Marshall Citrate solution* - The **Ross Marshall Citrate solution** was an older solution primarily used for **kidney preservation**. - It has been largely **superseded by newer solutions** with improved efficacy for liver and other organ preservation. *Kyoto ET solution* - **Kyoto ET solution** is another preservation solution primarily used in **Japan**, particularly for **kidney and pancreas preservation**. - While effective for those organs, it is **not the most commonly used** or preferred solution for liver preservation globally.