Membrane Lipids and Fluidity — MCQs
Which factor predominantly influences the rightward shift of the oxygen dissociation curve?
What determines the movement of water-insoluble substances in the body?
Which of the following is not amphipathic?
Which of the following is a major component of the plasma membrane?
Phospholipid associated with the mechanism of hormone action is
Maximum fluidity of the cell membrane is due to?
Proteoglycan present in the glomerular basement membrane is?
Two particles have the same diameter and molecular weight. Which factor would LEAST likely affect their passage through the glomerular filtration barrier?
A 45-year-old farmer presents with right upper quadrant pain and a history of exposure to livestock. An abdominal ultrasound shows a cystic lesion in the liver with internal floating membranes, described as the "Water lily sign." Based on this finding, what is the most likely Gharbi classification stage of the hydatid cyst?
Which of the following is a layer between choroid and retina?
Membrane Lipids and Fluidity Indian Medical PG Practice Questions and MCQs
Question 1: Which factor predominantly influences the rightward shift of the oxygen dissociation curve?
- A. pH (Bohr effect)
- B. 2,3-Bisphosphoglycerate (2,3-BPG) (Correct Answer)
- C. Temperature increase
- D. Carbon monoxide levels
Explanation: ***2,3-Bisphosphoglycerate (2,3-BPG)*** - **2,3-BPG** is an organic phosphate found in **red blood cells** that serves as the **predominant regulator** of oxygen-hemoglobin affinity under physiological conditions. - An increase in **2,3-BPG** levels binds to the **beta chains of deoxyhemoglobin**, stabilizing the T (tense) state and reducing hemoglobin's affinity for oxygen, thereby shifting the curve to the right and facilitating **oxygen release** to tissues. - **2,3-BPG** is especially important in **chronic adaptations** to hypoxia (high altitude, chronic lung disease, anemia) and is the **primary mechanism** for sustained alterations in oxygen delivery. - Normal RBC 2,3-BPG concentration is approximately equal to hemoglobin concentration, making it a **quantitatively significant** regulatory factor. *pH (Bohr effect)* - A decrease in blood **pH** (increased acidity) due to higher **CO2** and **H+** concentrations also shifts the oxygen dissociation curve to the right via the **Bohr effect**. - While physiologically important for **acute regulation** in metabolically active tissues, the Bohr effect operates in conjunction with other factors rather than as the predominant standalone regulator. - The effect is mediated by **protonation of histidine residues** on hemoglobin, causing conformational changes that reduce oxygen affinity. *Temperature increase* - An increase in **temperature** reduces hemoglobin's affinity for oxygen, shifting the oxygen dissociation curve to the right. - This effect is vital for **oxygen delivery** to actively metabolizing tissues (which generate heat), but is generally a **secondary factor** compared to 2,3-BPG in terms of overall regulation. - The temperature effect is more situational, occurring primarily in tissues with elevated metabolic activity. *Carbon monoxide levels* - **Carbon monoxide (CO)** causes a **leftward shift** of the oxygen dissociation curve, not a rightward shift. - CO binds to hemoglobin with 200-250 times greater affinity than oxygen, forming **carboxyhemoglobin** (COHb). - This not only reduces oxygen-carrying capacity but also **increases hemoglobin's affinity** for the remaining oxygen, making it harder to release oxygen to tissues. - CO poisoning is therefore dangerous both because it displaces oxygen and because it impairs oxygen delivery through leftward shift.
Question 2: What determines the movement of water-insoluble substances in the body?
- A. Hydrated diameter of molecule
- B. Molecular weight
- C. Lipid solubility (Correct Answer)
- D. Charge
Explanation: ***Lipid solubility*** - The movement of water-insoluble (lipophilic) substances across biological membranes is primarily determined by their **lipid solubility**, as these membranes are composed of a **lipid bilayer**. - Highly lipid-soluble substances can readily dissolve in the membrane and pass through via **simple diffusion**, following their concentration gradient. *Hydrated diameter of molecule* - This factor is more relevant for the movement of **water-soluble substances** through aqueous channels or pores. - Large hydrated diameters hinder movement through such channels, but it does not dictate the movement of water-insoluble substances across the lipid bilayer. *Molecular weight* - While molecular weight can generally influence diffusion rates, **lipid solubility** is a more critical determinant for water-insoluble substances moving across lipid membranes. - A substance with a higher molecular weight but significantly greater lipid solubility will often cross a membrane more easily than a substance with a lower molecular weight but poor lipid solubility. *Charge* - The charge of a molecule primarily affects its interaction with other charged molecules and its ability to traverse the **hydrophobic lipid bilayer** of cell membranes. - Charged molecules, even if small, are generally **water-soluble** and have difficulty crossing lipid membranes unless specific transporters or channels are involved.
Question 3: Which of the following is not amphipathic?
- A. Triglycerides (Correct Answer)
- B. Sphingolipids
- C. Glycolipids
- D. Phosphoglycerol
Explanation: ***Triglycerides*** - Triglycerides are composed of a **glycerol backbone** esterified to three fatty acids, making them entirely **hydrophobic** and thus not amphipathic. - They serve primarily as **energy storage** molecules and do not form membranes because they lack a polar head group. *Sphingolipids* - Sphingolipids are amphipathic because they contain a **hydrophilic polar head group** (e.g., phosphocholine or a sugar) and two **hydrophobic tails** derived from a fatty acid and the sphingosine backbone. - This dual nature allows them to be fundamental components of **cell membranes**. *Glycolipids* - Glycolipids are characterized by a **carbohydrate head group** attached to a lipid moiety, rendering them amphipathic. - The sugar portion is **hydrophilic**, while the lipid portion (e.g., ceramide) is **hydrophobic**, enabling them to participate in cell recognition and membrane stability. *Phosphoglycerol* - Phosphoglycerol (more commonly referred to as **glycerophospholipids**) are amphipathic, consisting of a **glycerol backbone**, two fatty acid tails, and a **phosphate group** often linked to an alcohol. - The **phosphate and alcohol group** form the hydrophilic head, and the **fatty acid tails** form the hydrophobic region, making them crucial for lipid bilayers.
Question 4: Which of the following is a major component of the plasma membrane?
- A. Protein
- B. Carbohydrate
- C. Cholesterol
- D. Phospholipid (Correct Answer)
Explanation: ***Phospholipid*** - **Phospholipids** form the fundamental **phospholipid bilayer** structure of the plasma membrane, acting as a barrier. - Their **amphipathic nature** (hydrophilic head and hydrophobic tails) allows them to spontaneously form this bilayer in an aqueous environment. *Carbohydrate* - **Carbohydrates** are present on the outer surface of the plasma membrane, forming the **glycocalyx**, but are not a major structural component of the bilayer itself. - They primarily function in **cell recognition** and adhesion. *Protein* - **Proteins** are embedded within or associated with the phospholipid bilayer, facilitating various functions like **transport**, signaling, and adhesion. - While crucial for function, they do not form the basic structural framework of the membrane. *Cholesterol* - **Cholesterol** is a type of lipid that helps regulate the **fluidity** and stability of the plasma membrane. - It is interspersed within the phospholipid bilayer but is not the primary structural component.
Question 5: Phospholipid associated with the mechanism of hormone action is
- A. Phosphatidylcholine
- B. Phosphatidylethanolamine
- C. Plasmalogen
- D. Phosphatidylinositol (Correct Answer)
Explanation: ***Phosphatidylinositol*** (Correct) - **Phosphatidylinositol (PI)** and its phosphorylated derivatives, particularly **PIP2 (phosphatidylinositol 4,5-bisphosphate)**, are critical in signal transduction pathways activated by many hormones. - Hormones binding to **G protein-coupled receptors** can activate phospholipase C, which cleaves PIP2 into **inositol triphosphate (IP3)** and **diacylglycerol (DAG)**, leading to increased intracellular calcium and protein kinase C activation, respectively. *Phosphatidylcholine* (Incorrect) - **Phosphatidylcholine** is a major component of cell membranes and is involved in membrane structure and fluidity. - While it can be a source of signaling molecules like **lysophosphatidic acid**, it is not primarily associated with the initial intracellular signaling events of hormone action in the same way as phosphatidylinositol. *Phosphatidylethanolamine* (Incorrect) - **Phosphatidylethanolamine** is another abundant membrane phospholipid primarily involved in membrane structure and stability. - It can be a precursor for other lipids, but it does not directly participate in the **second messenger systems** triggered by most hormones as a primary signaling molecule. *Plasmalogen* (Incorrect) - **Plasmalogens** are a unique class of phospholipids containing an ether bond at the sn-1 position. - They are abundant in certain tissues, particularly nervous and cardiovascular tissues, and are thought to have antioxidant properties, but they are not directly involved in the initiating events of **hormone signaling pathways**.
Question 6: Maximum fluidity of the cell membrane is due to?
- A. palmitic acid
- B. alpha-linolenic acid
- C. arachidonic acid (Correct Answer)
- D. linoleic acid (18:2)
Explanation: ***arachidonic acid*** - **Arachidonic acid** is a polyunsaturated fatty acid (PUFA) with 20 carbons and 4 double bonds, denoted as C20:4. The presence of multiple **double bonds** creates kinks in the fatty acid tails, preventing tight packing of phospholipids in the membrane and thus increasing fluidity. - Cell membrane fluidity is enhanced by **unsaturated fatty acids** due to the presence of C=C double bonds. The more double bonds a fatty acid has (i.e., higher degree of unsaturation), the greater its contribution to membrane fluidity. Since arachidonic acid has the most double bonds among the options, it confers the greatest fluidity. *alpha-linolenic acid* - **Alpha-linolenic acid** is an omega-3 fatty acid (C18:3). While it is a **polyunsaturated fatty acid** and contributes to fluidity, it has fewer double bonds (3) than arachidonic acid (4), making it less effective in maximizing fluidity compared to arachidonic acid. - Its presence increases membrane fluidity, but not to the same extent as fatty acids with a higher degree of unsaturation. *linoleic acid (18:2)* - **Linoleic acid** (C18:2) is an omega-6 fatty acid with two double bonds. It contributes to membrane fluidity because it is unsaturated, but **less so than fatty acids with more double bonds** such as alpha-linolenic acid or arachidonic acid. - The fewer double bonds mean the fatty acid tails can pack a bit more closely, offering less fluidity compared to highly unsaturated fatty acids. *palmitic acid* - **Palmitic acid** is a **saturated fatty acid** (C16:0), meaning it has no double bonds. Saturated fatty acids have straight hydrocarbon chains that can pack tightly together in the cell membrane. - This tight packing **reduces membrane fluidity** and makes the membrane more rigid, which is the opposite of what maximizes fluidity.
Question 7: Proteoglycan present in the glomerular basement membrane is?
- A. Keratan sulfate 1
- B. Keratan sulfate 2
- C. Heparan sulfate (Correct Answer)
- D. Chondroitin sulfate
Explanation: ***Heparan sulphate*** - Heparan sulphate is a key component of the **glomerular basement membrane** (GBM), crucial for its **negative charge and filtration function** [1][2]. - It plays a significant role in **filtration barrier** properties and affects the permeability of the GBM to proteins [1]. *Keratan sulphate 1* - Predominantly found in **cartilage** and **corneal tissue**, not associated with the glomerular basement membrane. - It contributes to **mechanical support** but lacks the essential role in renal filtration. *Keratan sulphate 2* - Similar to Keratan sulphate 1, this variant is involved in **cartilage** but not in the structure of the glomerular basement membrane. - Has distinct functions related to **tissue hydration** rather than the filtration dynamics of the GBM. *Chondroitin sulphate* - Commonly located in **cartilage** and connective tissues, it does not play a significant role in the structure of the glomerular basement membrane. - While it assists in **cell signaling** and regeneration, it does not influence the GBM permeability like heparan sulphate. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 905-907. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 34-35.
Question 8: Two particles have the same diameter and molecular weight. Which factor would LEAST likely affect their passage through the glomerular filtration barrier?
- A. Positively charged particles
- B. Charge does not affect passage
- C. Negatively charged particles
- D. Either charge can pass (Correct Answer)
Explanation: ***Either charge can pass*** - When two particles have the **same diameter and molecular weight**, charge becomes the primary differentiating factor for glomerular filtration - However, the question asks which factor would **LEAST affect passage** - both positively and negatively charged particles **CAN pass through** the glomerular filtration barrier, though at different rates - While charge significantly affects the **rate** of filtration, it does not create an absolute barrier - this makes "either charge can pass" the most accurate answer as it represents the least absolute effect on passage capability - The **glomerular basement membrane** contains negatively charged **heparan sulfate proteoglycans**, creating charge selectivity but not complete exclusion *Positively charged particles* - **Positively charged particles** filter **more readily** through the glomerular barrier due to electrostatic attraction to the negatively charged basement membrane - This represents a significant effect on passage rate, making charge a major factor for these particles - The enhanced filtration of cationic molecules is a well-established principle in renal physiology *Negatively charged particles* - **Negatively charged particles** are **relatively restricted** from passing through due to electrostatic repulsion from the negatively charged basement membrane - This significant hindrance to filtration demonstrates that charge strongly affects passage for anionic molecules - Albumin (negatively charged) is largely excluded from filtration partly due to charge repulsion *Charge does not affect passage* - This statement is **physiologically incorrect** - **Charge is a critical determinant** of glomerular permeability, along with size and shape - The charge selectivity of the glomerular barrier is fundamental to renal physiology and prevents excessive protein loss
Question 9: A 45-year-old farmer presents with right upper quadrant pain and a history of exposure to livestock. An abdominal ultrasound shows a cystic lesion in the liver with internal floating membranes, described as the "Water lily sign." Based on this finding, what is the most likely Gharbi classification stage of the hydatid cyst?
- A. Gharbi Stage I
- B. Gharbi Stage II
- C. Gharbi Stage III (Correct Answer)
- D. Gharbi Stage IV
Explanation: ***Gharbi Stage III*** - This stage is characterized by a **cystic lesion with internal floating membranes** (daughter cysts or detached endocyst), which is consistent with the "Water lily sign" described. - The membranes are indicative of a **degenerating or ruptured endocyst** within the main cyst, signifying a more advanced stage than simple cysts. *Gharbi Stage I* - This stage represents a **simple, unilocular cyst** with an anechoic (fluid-filled) lumen, without any internal structures or membranes. - It would appear as a clearly defined, fluid-filled mass with a smooth wall, lacking the internal complexity shown in the image. *Gharbi Stage II* - Gharbi Stage II is characterized by a **cyst with internal septations**, indicating the presence of multiple daughter cysts within the main cyst. - While it involves internal structures, these are typically well-defined septa rather than freely moving, detached membranes. *Gharbi Stage IV* - This stage describes a **heterogeneous, degenerating cyst** with a solid-like appearance, often without a clear cystic lumen. - It reflects a more advanced, often calcified or completely inactivated cyst, which does not match the clear cystic structure with floating membranes seen in the image.
Question 10: Which of the following is a layer between choroid and retina?
- A. Photoreceptors
- B. Descemet's membrane
- C. Ganglion cell layer
- D. Bruch's membrane (Correct Answer)
Explanation: ***Bruch's membrane*** - **Bruch's membrane** is an acellular barrier located between the **retinal pigment epithelium (RPE)** of the retina and the **choriocapillaris** layer of the choroid [1]. - Its primary function is to serve as a **filtration barrier** and to support the outer retina, playing a crucial role in nutrient and waste exchange [4]. *Photoreceptors* - The **photoreceptor layer** is part of the **retina** itself, containing the rods and cones responsible for light detection, and is not a separate layer between the choroid and retina [2]. - This layer sits **distal to the RPE** and Bruch's membrane, meaning it is closer to the center of the eye. *Descemet's membrane* - **Descemet's membrane** is an elastic and strong basement membrane found in the **cornea**, specifically between the corneal stroma and the corneal endothelium [2]. - It is located at the **front of the eye** and has no relation to the structures between the choroid and retina. *Ganglion cell layer* - The **ganglion cell layer** is a part of the **retina** that contains the cell bodies of the retinal ganglion cells, which transmit visual information from the eye to the brain [3]. - This layer is located **anterior to the photoreceptor layer** and is not situated between the choroid and retina.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free