Biochemistry
5 questionsWhat is the primary receptor for High-Density Lipoprotein (HDL) in cholesterol metabolism?
Which of the following compounds is not formed with the involvement of glycine?
Coenzyme for phenylalanine hydroxylase is?
Creatinine is formed from -
In phenylketonuria, which substance should be restricted in the diet?
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 431: What is the primary receptor for High-Density Lipoprotein (HDL) in cholesterol metabolism?
- A. SR-BI (Correct Answer)
- B. LDLR
- C. HDLR
- D. SR-82
Explanation: ***SR-BI*** - **Scavenger Receptor class B type 1 (SR-BI)** is the primary receptor responsible for selective uptake of **cholesteryl esters** from HDL into cells, particularly the liver and steroidogenic tissues. - Unlike other lipoprotein receptors, SR-BI mediates the **selective transfer** of cholesterol without internalizing the entire HDL particle. *LDLR* - The **Low-Density Lipoprotein Receptor (LDLR)** is the primary receptor for **LDL** and very low-density lipoprotein (VLDL) remnants, mediating their endocytosis and degradation. - While it plays a crucial role in cholesterol metabolism, its main function is related to the uptake of **LDL cholesterol**, not HDL. *HDLR* - **HDLR** is not a recognized receptor in cholesterol metabolism. - This term may be a distracter created by combining HDL with the common receptor nomenclature. *SR-82* - **SR-82** is not a recognized receptor involved in cholesterol metabolism. - Similar to HDLR, this is a distracter term.
Question 432: Which of the following compounds is not formed with the involvement of glycine?
- A. Purines
- B. Glutathione
- C. Thyroxine (Correct Answer)
- D. Heme
Explanation: ***Thyroxine*** - **Thyroxine** (and other thyroid hormones) are derived from the amino acid **tyrosine**. - Their synthesis involves iodination and coupling reactions of tyrosine residues within the protein **thyroglobulin**. *Heme* - **Glycine** is a direct precursor for the initial step in **heme synthesis**. - It condenses with **succinyl CoA** to form α-amino-β-ketoadipate, which then decarboxylates to form δ-aminolevulinate (ALA). *Purines* - **Glycine** contributes part of its structure to the **purine ring**. - Specifically, the **nitrogen at position 7** and the **carbons at positions 4 and 5** of the purine ring are derived from glycine. *Glutathione* - **Glutathione** is a tripeptide composed of three amino acids: **glutamate**, **cysteine**, and **glycine**. - **Glycine** is the C-terminal amino acid of glutathione and is essential for its structure and function as an antioxidant.
Question 433: Coenzyme for phenylalanine hydroxylase is?
- A. Tetrahydrofolate
- B. Pyridoxal phosphate
- C. S-adenosyl methionine
- D. Tetrahydrobiopterin (Correct Answer)
Explanation: ***Tetrahydrobiopterin*** - **Tetrahydrobiopterin (BH4)** is an essential coenzyme for aromatic amino acid hydroxylases, including **phenylalanine hydroxylase (PAH)**. - PAH converts **phenylalanine** to **tyrosine**, and deficiencies in BH4 or PAH itself lead to *phenylketonuria (PKU)*. *Tetrahydrofolate* - **Tetrahydrofolate (THF)** is a coenzyme derived from **folic acid** and is primarily involved in **one-carbon metabolism**, including **purine** and **pyrimidine synthesis**, and various amino acid interconversions. - It does not directly act as a coenzyme for phenylalanine hydroxylase. *Pyridoxal phosphate* - **Pyridoxal phosphate (PLP)**, a derivative of **vitamin B6**, is a crucial coenzyme for many enzymes involved in **amino acid metabolism**, particularly in **transamination**, **decarboxylation**, and side-chain cleavage reactions. - It is not the coenzyme for phenylalanine hydroxylase. *S-adenosyl methionine* - **S-adenosyl methionine (SAM)** is a major **methyl donor** in various biochemical reactions, important for the synthesis of **neurotransmitters**, **hormones**, and **phospholipids**. - While essential for many metabolic pathways, it is not involved as a coenzyme for phenylalanine hydroxylase.
Question 434: Creatinine is formed from -
- A. Creatine (Correct Answer)
- B. Lysine
- C. Leucine
- D. Histidine
Explanation: ***Creatine*** - **Creatinine** is a waste product formed from the non-enzymatic, irreversible degradation of **creatine** and **creatine phosphate**, primarily in muscles. - **Creatine** itself is synthesized endogenously from three amino acids: **glycine, arginine, and methionine** (as S-adenosylmethionine) through a two-step enzymatic process in the kidney and liver. - The amount of creatinine produced daily is relatively constant and directly proportional to an individual's **muscle mass**, making it a useful marker for renal function. *Lysine* - **Lysine** is an **essential amino acid** and a precursor for various compounds like **carnitine** but is not involved in creatinine or creatine formation. - Deficiency can lead to impaired protein synthesis but does not impact creatinine levels. *Leucine* - **Leucine** is another **essential amino acid** and a **branched-chain amino acid (BCAA)** crucial for muscle protein synthesis and repair. - It does not serve as a direct precursor for creatinine or creatine. *Histidine* - **Histidine** is an **essential amino acid** and a precursor for **histamine** and other important compounds, but not creatinine or creatine. - It plays roles in immune response and gastric acid secretion.
Question 435: In phenylketonuria, which substance should be restricted in the diet?
- A. Tyrosine
- B. Phenylalanine (Correct Answer)
- C. Maize
- D. None of the options
Explanation: ***Phenylalanine*** - **Phenylketonuria (PKU)** is a genetic disorder where the body cannot effectively metabolize **phenylalanine** due to a deficiency in the enzyme **phenylalanine hydroxylase**. - Restricting dietary phenylalanine is crucial to prevent the accumulation of toxic byproducts that can lead to severe neurological damage and developmental delays. *Tyrosine* - Tyrosine is normally synthesized from phenylalanine. In PKU, this conversion is impaired. - While phenylalanine must be restricted, tyrosine supplementation is often necessary for individuals with PKU, as it becomes a conditionally essential amino acid. *Maize* - Maize (corn) is a carbohydrate-rich food and does not contain high levels of phenylalanine that would necessitate its restriction in PKU. - Dietary management in PKU focuses on regulating protein intake, as phenylalanine is an amino acid found in proteins. *None of the options* - This option is incorrect because phenylalanine must be strictly restricted in the diet of individuals with phenylketonuria to manage the condition effectively. - Without dietary restriction, the accumulation of phenylalanine can lead to severe and irreversible neurological damage.
Internal Medicine
1 questionsWhich of the following is true regarding carcinoid tumor?
NEET-PG 2015 - Internal Medicine NEET-PG Practice Questions and MCQs
Question 431: Which of the following is true regarding carcinoid tumor?
- A. Associated with serotonin production
- B. Potentially malignant tumor
- C. Neuroendocrine tumor (Correct Answer)
- D. Most common site is lung
Explanation: ### Most common site is lung - Carcinoid tumors are more commonly found in the **gastrointestinal tract**, specifically the appendix and ileum, rather than the lungs [1]. - This statement is false as they can occur in the lungs but are not the most common site overall. ### Potentially malignant tumor - Carcinoid tumors can be classified as **malignant,** especially if they show aggressive behavior or metastasis. - Many carcinoid tumors, particularly those in the gastrointestinal tract, can be **non-functional** and less aggressive [1]. ### Neuroendocrine tumor - Carcinoid tumors are indeed a type of **neuroendocrine tumor**, arising from **neuroendocrine cells**. - This classification emphasizes their origin and potential for secretion of hormones like **serotonin**. ### Associated with serotonin production - Many carcinoid tumors produce **serotonin**, leading to symptoms like **carcinoid syndrome** when they metastasize, particularly to the liver [1]. - This statement is true, indicating their involvement in neuroendocrine secretions.
Pathology
1 questionsWhat does Ghon's focus indicate in the context of tuberculosis?
NEET-PG 2015 - Pathology NEET-PG Practice Questions and MCQs
Question 431: What does Ghon's focus indicate in the context of tuberculosis?
- A. Primary complex (Correct Answer)
- B. Post primary tuberculosis
- C. Miliary tuberculosis
- D. Tuberculous lymphadenitis
Explanation: ***Primary complex*** - A **Ghon's focus** is the initial parenchymal lesion (typically subpleural) that develops during primary tuberculosis infection [1]. - The Ghon's focus, together with an enlarged regional lymph node (usually hilar or mediastinal), forms the **Ghon's complex** or **Primary complex** [2]. - When this complex undergoes calcification and healing, it is called a **Ranke complex**, which indicates past healed primary TB. *Post primary tuberculosis* - Also known as **reactivation tuberculosis** or **secondary tuberculosis**, this typically occurs years after the primary infection, usually in the apices of the lungs [2]. - It represents reactivation of dormant bacilli, not the initial primary infection lesion. - Characterized by cavitary lesions and often more severe pulmonary symptoms. *Miliary tuberculosis* - This is a form of progressive, widespread tuberculosis characterized by the presence of **tiny, millet-seed sized lesions** disseminated throughout the body via hematogenous spread [3]. - It indicates a severe and life-threatening form of TB resulting from massive lymphohematogenous dissemination. - Not related to the localized primary complex. *Tuberculous lymphadenitis* - This refers to **tuberculous infection of lymph nodes**, most commonly in the cervical region (scrofula). - While lymph node involvement is part of the primary complex, Ghon's focus specifically refers to the **parenchymal lung lesion**, not the lymph node component alone [2]. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 379-380. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 319-320. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Respiratory Tract Disease, pp. 320-321.
Physiology
2 questionsWhich of the following is a potassium Channelopathy?
Increase in plasma viscosity is maximally caused by which plasma protein?
NEET-PG 2015 - Physiology NEET-PG Practice Questions and MCQs
Question 431: 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.
Question 432: Increase in plasma viscosity is maximally caused by which plasma protein?
- A. Albumin
- B. All have equal effect
- C. Globulin
- D. Fibrinogen (Correct Answer)
Explanation: ***Globulin*** - Increased levels of **globulin** proteins, particularly in inflammatory or proliferative conditions, have a significant impact on plasma viscosity due to their **high molecular weight** [1]. - **Globulins** contribute to **hyperviscosity syndrome**, which can lead to clinical symptoms like fatigue and visual disturbances [1]. *Albumin* - While **albumin** is the most abundant plasma protein, its primary role is in maintaining **oncotic pressure**, not significantly affecting plasma viscosity. - An increase in albumin does not correlate with plasma viscosity increases to the extent seen with globulins. *All have equal effect* - Different plasma proteins do not have **equal effects** on viscosity; **globulins** and **fibrinogen** particularly influence it more than **albumin**. - The impact on viscosity varies significantly with protein concentration and type, making this statement inaccurate. *Fibrinogen* - **Fibrinogen** does contribute to plasma viscosity but is typically less than that caused by globulins, especially when globulin levels are markedly elevated. - Its effect is more pronounced during **coagulation**, rather than in the general increase of plasma viscosity associated with inflammatory states. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 141-142.
Surgery
1 questionsSolution currently used for liver preservation for transplantation is?
NEET-PG 2015 - Surgery NEET-PG Practice Questions and MCQs
Question 431: 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.