Membrane Biochemistry Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Membrane Biochemistry. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Membrane Biochemistry Indian Medical PG Question 1: Which of the following factors acts in vesicle targeting?
- A. Sec 12
- B. Rab (Correct Answer)
- C. Ras
- D. SNARE
Membrane Biochemistry Explanation: ***Rab***
- **Rab GTPases** are small G proteins that regulate many steps of membrane trafficking, including vesicle formation, cargo selection, vesicle budding, uncoating, motility, and fusion.
- They act as molecular switches, cycling between an active GTP-bound state and an inactive GDP-bound state, thereby coordinating the proper targeting of vesicles to their destination membranes.
*Sec 12*
- **Sec12** is a **GEF (guanine nucleotide exchange factor)** for **Sar1**, which is involved in COPII vesicle formation from the ER.
- While it initiates a step in vesicle budding, it does not directly act as a targeting molecule to guide the vesicle to its destination.
*Ras*
- **Ras GTPases** are primarily involved in cell signaling pathways regulating cell proliferation, differentiation, and survival.
- They are not directly involved in the process of **vesicle targeting** in membrane trafficking.
*SNARE*
- **SNARE proteins** (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) are crucial for the **fusion of vesicles** with their target membranes.
- While essential for the later stages of trafficking, they mediate membrane fusion rather than initial vesicle targeting.
Membrane Biochemistry Indian Medical PG Question 2: What is the main component of a bilayer cell membrane?
- A. Cholesterol ester
- B. Triacyl glycerol
- C. Cholesterol
- D. Phospholipids (Correct Answer)
Membrane Biochemistry Explanation: ***Correct: Phospholipids***
- **Phospholipids** are the primary structural components of cell membranes, forming a **bilayer** due to their amphipathic nature.
- The **hydrophilic heads** face the aqueous environment, while the **hydrophobic tails** form the core of the membrane.
*Incorrect: Cholesterol*
- **Cholesterol** is an important component of animal cell membranes, contributing to fluidity and stability, but it is not the **main structural component**.
- It inserts between phospholipids, modulating membrane fluidity by preventing the tight packing of fatty acid tails at lower temperatures and hindering excessive movement at higher temperatures.
*Incorrect: Cholesterol ester*
- **Cholesterol esters** are storage forms of cholesterol and are primarily found in intracellular lipid droplets or associated with lipoproteins in the bloodstream.
- They are generally too **hydrophobic** to be significant structural components within the phospholipid bilayer itself.
*Incorrect: Triacyl glycerol*
- **Triacylglycerols** (triglycerides) are the primary form of **energy storage** in cells, found in lipid droplets within the cytoplasm.
- They are highly **hydrophobic** and do not form a structural part of the cell membrane bilayer.
Membrane Biochemistry Indian Medical PG Question 3: With reference to human body's requirement for proteins, they are essential because they are:
1. an important alternative source for energy during specific metabolic states.
2. the primary molecules responsible for maintenance of osmotic pressure within the extracellular compartment.
3. critical for upkeep of cell mediated immune response.
4. vital for the synthesis of certain hormones.
Which of the statements given above are correct?
- A. 2, 3 and 4
- B. 1, 2 and 3
- C. 1, 3 and 4 (Correct Answer)
- D. 1, 2 and 4
Membrane Biochemistry Explanation: ***1, 3 and 4***
- Proteins can be used as an **alternative energy source** during specific metabolic states, such as prolonged fasting or starvation, when carbohydrate and fat stores are depleted, through processes like **gluconeogenesis** and protein catabolism.
- Proteins are critical for the **cell-mediated immune response**, as T-lymphocytes, cytokines, MHC proteins, and various immune mediators are protein-based. Protein-energy malnutrition significantly impairs cell-mediated immunity.
- Many hormones, such as **insulin**, **growth hormone**, **ACTH**, and various **peptide hormones**, are protein-based or derived from amino acids, making proteins vital for hormone synthesis.
*2, 3 and 4*
- Statement 2 is **incorrect** because while proteins (particularly albumin) do contribute to osmotic pressure in the **intravascular compartment**, the statement refers to the "extracellular compartment" broadly, where **electrolytes (especially sodium)** are the primary molecules responsible for osmotic pressure maintenance, not proteins.
- Proteins contribute to **oncotic pressure** (colloid osmotic pressure) specifically, which is distinct from total osmotic pressure.
*1, 2 and 3*
- This option incorrectly includes statement 2, which overstates the role of proteins in osmotic pressure across the entire extracellular compartment.
- It correctly identifies proteins as an energy source and their role in cell-mediated immunity, but fails to include their vital role in **hormone synthesis**.
*1, 2 and 4*
- This option incorrectly includes statement 2 about osmotic pressure in the extracellular compartment.
- It correctly recognizes proteins as an alternative energy source and for hormone synthesis, but omits their critical role in the **cell-mediated immune response**.
Membrane Biochemistry Indian Medical PG Question 4: Which of the following is a feature not typically associated with Hereditary Spherocytosis?
- A. Gall stones
- B. Direct Coombs Positive (Correct Answer)
- C. Splenomegaly
- D. Increased Osmotic Fragility
Membrane Biochemistry Explanation: ***Direct Coomb's Positive***
- In Hereditary Spherocytosis, the **Coomb's test** is typically **negative**, indicating that hemolysis is not due to autoimmune factors.
- Presence of **spherocytes** on the blood smear and increased fragility are hallmark findings, not antibodies against red cells [1].
*Splenomegaly*
- **Splenomegaly** is common in Hereditary Spherocytosis as the spleen actively removes abnormal spherocytes from circulation [1].
- It can lead to **hypersplenism**, with resultant anemia and thrombocytopenia.
*Increased Osmotic Fragility*
- Increased osmotic fragility is a key feature of Hereditary Spherocytosis, as red blood cells are less able to withstand hypotonic solutions [1].
- This results from a defect in the red cell membrane, causing spherocyte shape and fragility.
*Gall stones*
- Patients may develop **gallstones** due to increased bilirubin from the breakdown of spherocytes, leading to **bilirubin stones** [1].
- Gallstones are a common complication due to chronic hemolysis.
**References:**
[1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 597-598.
Membrane Biochemistry Indian Medical PG Question 5: Equilibrium potential of calcium is
- A. +130mV (Correct Answer)
- B. -32mV
- C. +65mV
- D. -95mV
Membrane Biochemistry Explanation: ***+130mV***
- The **equilibrium potential** for an ion is the **membrane potential** at which the net movement of that ion across the membrane is zero, even if there is a concentration gradient.
- Due to the significantly higher extracellular concentration of **calcium ions (Ca2+)** relative to the intracellular concentration, a large positive membrane potential is required to prevent Ca2+ influx.
*-32mV*
- This value does not represent the typical **equilibrium potential** for any major physiological ion like sodium, potassium, chloride, or calcium in mammalian cells.
- Equilibrium potentials are highly dependent on the **concentration gradients** of the specific ion.
*+65mV*
- This value is close to the typical **equilibrium potential for sodium (Na+)**, which is approximately +60 to +70 mV in many cells, due to its outward concentration gradient.
- **Calcium's equilibrium potential** is much more positive than sodium's due to its larger concentration gradient and its divalent charge.
*-95mV*
- This value is close to the typical **equilibrium potential for potassium (K+)**, which is approximately -90 to -95 mV, reflecting the movement of potassium out of the cell.
- The **equilibrium potential for calcium** is highly positive, whereas this negative value suggests an inward current for a positively charged ion.
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