Biochemistry
7 questionsWhat is the major site of protein glycosylation?
Which element is required by phosphofructokinase?
Carboxypeptidase contains which mineral?
What is the typical Q10 value for enzymatic reactions?
What type of enzyme is hexokinase?
Which of the following enzymes is classified as a serine protease?
Which is the primary energy molecule that gives approximately 7.3 kcal/mol?
NEET-PG 2013 - Biochemistry NEET-PG Practice Questions and MCQs
Question 391: What is the major site of protein glycosylation?
- A. Ribosome and Golgi body
- B. ER and Ribosome
- C. Ribosome and Cytoplasm
- D. ER and Golgi body (Correct Answer)
Explanation: ***ER and Golgi body*** - The **endoplasmic reticulum (ER)** is the primary site for **N-linked glycosylation**, where carbohydrates are added to the asparagine residues of nascent proteins. - The **Golgi apparatus** is crucial for further modification and processing of these N-linked glycans, as well as the site for **O-linked glycosylation**, where sugars are added to serine or threonine residues. *Ribosome and Golgi body* - **Ribosomes** are responsible for **protein synthesis (translation)** but do not directly perform glycosylation, which is a post-translational modification. - While the **Golgi body** is a site of glycosylation, the ribosome's inclusion makes this option incorrect as the ribosome's role precedes glycosylation. *ER and Ribosome* - The **ER** is a major site of protein glycosylation, especially N-linked glycosylation. - However, **ribosomes** are involved in protein synthesis and lack the enzymatic machinery for adding sugar moieties to proteins. *Ribosome and Cytoplasm* - **Ribosomes** synthesize proteins, but glycosylation does not occur there. - The **cytoplasm** is the site for many metabolic pathways, but major protein glycosylation events mostly occur within the ER and Golgi.
Question 392: Which element is required by phosphofructokinase?
- A. Magnesium (Correct Answer)
- B. Inorganic phosphate
- C. Manganese
- D. Copper
Explanation: **Magnesium** - **Phosphofructokinase** (PFK) is an enzyme in **glycolysis** that catalyzes the phosphorylation of fructose-6-phosphate. - This reaction requires **ATP**, and like many enzymes that utilize ATP, PFK requires **magnesium ions (Mg²⁺)** as a cofactor, typically forming a complex with ATP (MgATP²⁻). *Inorganic phosphate* - **Inorganic phosphate** is a substrate for some kinase reactions, but not a direct cofactor requirement for the *activation* of phosphofructokinase itself. - While phosphate is incorporated into molecules during phosphorylation, it does not act as a metal ion cofactor to facilitate the enzyme's activity. *Manganese* - While **manganese (Mn²⁺)** can sometimes substitute for magnesium in certain enzyme reactions, it is not the primary or required cofactor for phosphofructokinase under normal physiological conditions. - Many enzymes have a preference for specific metal ions based on their active site structure and coordination chemistry. *Copper* - **Copper (Cu²⁺)** is a cofactor for a variety of enzymes, particularly those involved in **redox reactions** (e.g., cytochrome c oxidase, superoxide dismutase). - However, copper is not a required metallic cofactor for the activity of **phosphofructokinase** in glycolysis.
Question 393: Carboxypeptidase contains which mineral?
- A. Copper
- B. Zinc (Correct Answer)
- C. Iron
- D. None of the options
Explanation: ***Zinc*** - **Carboxypeptidase** is a **metalloenzyme**, meaning it requires a metal ion for its catalytic activity. - **Zinc** acts as a crucial cofactor in the active site of carboxypeptidase, enabling its proteolytic function. *Copper* - **Copper** is a component of enzymes like **cytochrome c oxidase** and **superoxide dismutase**, but not carboxypeptidase. - Its presence is essential for processes like **electron transport** and **antioxidant defense**. *Iron* - **Iron** is a central component of **hemoglobin** and **myoglobin** for oxygen transport, and in enzymes like **catalase** and **peroxidase**. - It is not involved in the catalytic mechanism of carboxypeptidase. *None of the options* - This option is incorrect because **Zinc** is a known and essential mineral for the function of carboxypeptidase. - Carboxypeptidase is a metalloenzyme, and a metal cofactor is required for its activity.
Question 394: What is the typical Q10 value for enzymatic reactions?
- A. 2 (Correct Answer)
- B. 3
- C. 4
- D. 5
Explanation: ***2*** - The **Q10 value** represents the factor by which the rate of a reaction increases for every 10°C rise in temperature. - For most enzymatic and biological reactions, the **Q10 value** is typically around **2 to 3**. *3* - While **3** is within the typical range for some biological reactions, **2** is often considered the most common or average value cited for enzymatic reactions. - A **Q10 of 3** means the reaction rate triples with a 10°C increase, which is observed in certain cases but is not the most general "typical" value. *4* - A **Q10 value of 4** indicates a significantly higher temperature sensitivity than what is commonly observed for most enzymatic reactions. - Such a high Q10 would imply that the reaction rate quadruples for every 10°C increase, which is less typical. *5* - A **Q10 value of 5** is exceptionally high and rarely observed for common enzymatic reactions under physiological conditions. - This would suggest an extreme sensitivity to temperature changes, which is not characteristic of most enzyme kinetics.
Question 395: What type of enzyme is hexokinase?
- A. Ligase
- B. Transferase (Correct Answer)
- C. Oxidoreductase
- D. Reductase
Explanation: ***Transferase*** - Hexokinase catalyzes the transfer of a **phosphate group** from **ATP** to glucose, forming glucose-6-phosphate. - Enzymes that catalyze the transfer of functional groups from one molecule to another are classified as **transferases**. *Ligase* - **Ligases** are enzymes that catalyze the joining of two large molecules by forming a new chemical bond, usually accompanied by the hydrolysis of a small pendant chemical group on one of the larger molecules or the less-stable of the two products. - This activity usually involves reactions like **DNA ligation**, not phosphate group transfer to a sugar. *Oxidoreductase* - **Oxidoreductases** catalyze **oxidation-reduction reactions**, involving the transfer of electrons from one molecule to another. - Hexokinase does not perform redox reactions; it transfers a phosphate group. *Reductase* - **Reductases** are a specific type of **oxidoreductase** that catalyze reactions where a molecule is reduced (gains electrons). - This is a subset of oxidation-reduction chemistry and is not the function of hexokinase.
Question 396: Which of the following enzymes is classified as a serine protease?
- A. Pepsin
- B. Trypsin (Correct Answer)
- C. Carboxypeptidase
- D. None of the options
Explanation: ***Trypsin*** - **Trypsin** is a digestive enzyme belonging to the **serine protease** family, characterized by a crucial **serine residue** in its active site. - It plays a vital role in protein digestion in the small intestine, cleaving peptide bonds on the carboxyl side of **lysine** or **arginine** residues. *Pepsin* - **Pepsin** is an aspartic protease, meaning it utilizes an **aspartate residue** in its active site for catalysis. - It primarily functions in the stomach, digesting proteins into smaller peptides in an **acidic environment**. *Carboxypeptidase* - **Carboxypeptidase** is a **metalloexopeptidase** that contains a zinc ion in its active site. - It removes amino acids one by one from the **carboxyl-terminal** end of polypeptide chains. *None of the options* - This option is incorrect because **trypsin** is indeed a well-known example of a serine protease.
Question 397: Which is the primary energy molecule that gives approximately 7.3 kcal/mol?
- A. ATP (Correct Answer)
- B. GTP
- C. Glucose-6-phosphate
- D. Creatine phosphate
Explanation: ***ATP*** - **Adenosine triphosphate (ATP)** is the primary energy currency of the cell, providing approximately **7.3 kcal/mol** upon hydrolysis of its terminal phosphate group. - This energy is released when ATP is converted to **ADP (adenosine diphosphate)** and an inorganic phosphate (Pi), driving various cellular processes. *GTP* - **Guanosine triphosphate (GTP)** is another nucleotide triphosphate that carries energy, but it is primarily involved in specific processes like **protein synthesis** and **signal transduction**, not as the ubiquitous primary energy molecule like ATP. - While it also releases energy upon hydrolysis, its standard free energy change is similar to ATP but it's not the main universal energy carrier. *Glucose-6-phosphate* - **Glucose-6-phosphate** is an important intermediate in **glycolysis** and **gluconeogenesis**, but it is not an energy-storing molecule in the same way as ATP. - Its high-energy phosphate bond is used in metabolic pathways, but it doesn't directly release 7.3 kcal/mol as a direct energy source for cellular work. *Creatine phosphate* - **Creatine phosphate** serves as an energy reserve in muscle and nerve cells, rapidly generating ATP from ADP during periods of intense activity. - While it is a high-energy phosphate compound, it functions to **replenish ATP** rather than being the direct energy molecule that performs cellular work.
Pathology
2 questionsWhich of the following statements about Polycythemia vera is false?
In which condition are Michaelis Gutmann bodies typically seen?
NEET-PG 2013 - Pathology NEET-PG Practice Questions and MCQs
Question 391: Which of the following statements about Polycythemia vera is false?
- A. Increased LAP score (Correct Answer)
- B. Increased vitamin B12 levels
- C. Leukocytosis is present
- D. Increased platelet count
Explanation: ***Decrease LAP score*** - In polycythemia vera, the **LAP (leukocyte alkaline phosphatase) score** is typically increased, indicating more mature leukocytes. - A **decrease in LAP score** is not consistent with the disease, making this statement incorrect. *Increased platelets* - Polycythemia vera often results in **thrombocytosis**, characterized by increased platelet counts [1]. - This is a common feature of the disorder, reflecting overproduction of blood cells in the bone marrow. *Leucocytosis* - Patients with polycythemia vera frequently exhibit **leucocytosis**, or increased white blood cell counts, due to hypercellularity of the bone marrow [1]. - This is an important aspect of the disease, often seen alongside increases in red blood cells and platelets. *Increased vit B12* - An elevation in **vitamin B12** levels can occur in polycythemia vera, often due to increased binding proteins. - This is a well-recognized phenomenon associated with the increased cell turnover in this condition. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of White Blood Cells, Lymph Nodes, Spleen, and Thymus, pp. 626-627.
Question 392: In which condition are Michaelis Gutmann bodies typically seen?
- A. Xanthogranulomatous
- B. Pyelonephritis
- C. Malakoplakia (Correct Answer)
- D. Nail patella syndrome
Explanation: ***Malakoplakia*** - **Michaelis-Gutmann bodies** are pathognomonic histological features of malakoplakia, representing calcified concretions containing **iron and calcium** within macrophages. - These are formed around **partially digested bacteria** within defective macrophages, appearing as basophilic inclusions with a "target-like" or "owl's eye" appearance. - Malakoplakia is a chronic granulomatous inflammatory condition most commonly affecting the **urinary tract** (bladder, kidney), but can occur in other organs. *Xanthogranulomatous* - This condition is characterized by an infiltrate of **lipid-laden macrophages** (xanthoma cells, foam cells) and occasional giant cells, but **not** Michaelis-Gutmann bodies. - It most commonly affects the kidney (**xanthogranulomatous pyelonephritis**) and is a destructive inflammatory process with a mass-like appearance. *Pyelonephritis* - Refers to **inflammation of the kidney and renal pelvis**, usually due to bacterial infection (commonly E. coli). - Histologically, it is characterized by acute or chronic inflammatory cells, neutrophil infiltration, and potential abscess formation, **without** Michaelis-Gutmann bodies. *Nail patella syndrome* - This is a **genetic disorder** (autosomal dominant) affecting primarily the **nails, bones** (absent/hypoplastic patella, elbow dysplasia), and sometimes the kidneys (glomerular disease). - It is associated with developmental abnormalities and has **no association** with Michaelis-Gutmann bodies or malakoplakia.
Pharmacology
1 questionsWhich of the following is not an ionic receptor?
NEET-PG 2013 - Pharmacology NEET-PG Practice Questions and MCQs
Question 391: Which of the following is not an ionic receptor?
- A. Kainate
- B. AMPA
- C. mGluR (Correct Answer)
- D. NMDA
Explanation: **Ionic receptors** (ionotropic receptors) are ligand-gated ion channels that open upon binding, allowing ions to flow directly through the channel. **Non-ionic receptors** (metabotropic receptors) are G-protein coupled receptors that activate intracellular signaling cascades. ***mGluR*** - **Metabotropic glutamate receptors (mGluRs)** are **G-protein coupled receptors** (GPCRs), meaning they activate intracellular signaling pathways rather than directly forming an ion channel. - Their activation leads to slower, longer-lasting changes in neuronal excitability through second messenger systems. - **This is the correct answer** as mGluRs are NOT ionic receptors. *NMDA* - **NMDA receptors** are **ionotropic glutamate receptors** that form ligand-gated ion channels permeable to calcium and sodium ions. - They are crucial for **synaptic plasticity** and learning. *Kainate* - **Kainate receptors** are also **ionotropic glutamate receptors** that are permeable to sodium and potassium ions. - They play diverse roles in synaptic transmission and neuronal excitability. *AMPA* - **AMPA receptors** are **ionotropic glutamate receptors** primarily responsible for fast excitatory synaptic transmission in the central nervous system. - They are permeable to sodium and potassium ions and mediate the majority of fast excitatory synaptic currents.