Q.63 Choose the correct statements:

A. Eukaryotes store energy as triacylglycerols in adipocytes.
B. Transfer of phosphatidylethanolamine (PE) to the outer surface of a cell is a signal for programmed cell death.
C. Integral membrane proteins are attached firmly with the lipid bilayer and can be removed by using detergents.
D. GPI anchored proteins preferentially are localized in the lipid rafts.
E. Plasma membrane of humans is rich in cardiolipin.

Choose the correct answer from the options given below:

1. A, B, C, D only
2. A, C, D only
3. A, B, C, D, E
4. A, C, E only

   Correct Answer: A, C, D only

   Eukaryotes indeed store energy as triacylglycerols primarily in adipocytes, integral membrane proteins require detergents for removal from the lipid bilayer, and GPI-anchored proteins localize preferentially in lipid rafts.

   Option Analysis

   A. Eukaryotes store energy as triacylglycerols in adipocytes

   True. Triacylglycerols (TAGs) serve as the main long-term energy reserve in eukaryotic cells, stored in lipid droplets within specialized adipocytes in animals.

   B. Transfer of phosphatidylethanolamine (PE) to the outer surface signals programmed cell death

   False. Exposure of phosphatidylserine (PS), not PE, on the outer leaflet of the plasma membrane acts as the key “eat-me” signal for apoptosis.

   C. Integral membrane proteins are attached firmly with the lipid bilayer and can be removed by using detergents

   True. These proteins embed via transmembrane hydrophobic domains; detergents disrupt the bilayer to form mixed micelles, solubilizing them.

   D. GPI anchored proteins preferentially are localized in lipid rafts

   True. GPI anchors are glycosylphosphatidylinositol lipids enriched in cholesterol-sphingolipid rafts, concentrating these proteins in ordered membrane domains.

   E. Plasma membrane of humans is rich in cardiolipin

   False. Cardiolipin predominates in mitochondrial inner membranes (up to 20%); human plasma membranes feature phosphatidylcholine, sphingomyelin, and cholesterol.

   Introduction to Membrane Biology Essentials

   In integral membrane proteins lipid bilayer detergents and GPI anchored proteins lipid rafts, understanding eukaryotic energy storage and membrane dynamics proves crucial for exams like GATE Life Sciences. This guide dissects a multiple-choice question on triacylglycerols, apoptosis signals, protein extraction, and lipid composition, matching your molecular biology focus.

   Energy Storage: Triacylglycerols in Eukaryotes

   Adipocytes pack neutral lipids like triacylglycerols into droplets for efficient energy storage, yielding over twice the calories per gram versus carbohydrates. This option (A) holds true across animals and plants.

   Apoptosis Signaling: Phospholipids Role

   Programmed cell death flips phosphatidylserine externally via flippases/scramblases, not phosphatidylethanolamine. Thus, B fails as PS—not PE—triggers phagocytosis.

   Extracting Integral Membrane Proteins

   Firmly transmembrane-anchored proteins resist mild agents; detergents partition into the bilayer above CMC, yielding protein-lipid micelles for purification. C is accurate.

   GPI Anchors and Lipid Rafts Localization

   Glycosylphosphatidylinositol tails tether proteins to raft microdomains, rich in sphingolipids/cholesterol, aiding signaling. D correctly identifies this preference.

   Cardiolipin in Human Plasma Membranes

   This diphosphatidylglycerol suits mitochondrial cristae for respiration but stays minor (~1-5%) in plasma membranes, dominated by PC and cholesterol. E is incorrect.

   Option	Statement Summary	Correct?	Key Reason
   A	Triacylglycerols in adipocytes	Yes	Primary energy storage form
   B	PE outer flip for apoptosis	No	PS, not PE, signals death
   C	Detergents remove integral proteins	Yes	Form solubilizing micelles
   D	GPI in lipid rafts	Yes	Raft lipid affinity
   E	Plasma rich in cardiolipin	No	Mitochondrial lipid