Q37. Which of the following lipids is non–ionic?
(A) Sphingomyelin
(B) Galactocerebroside
(C) Lecithin
(D) Phosphatidyl inositol
Galactocerebroside is the non-ionic lipid among the options. It lacks charged groups, unlike the others which contain phosphate-based headgroups that confer ionic or zwitterionic properties at physiological pH. This distinction is key for understanding lipid roles in cell membranes, especially for CSIR NET Life Sciences preparation.
Option Analysis
Sphingomyelin (A): Sphingomyelin features a phosphocholine headgroup attached to a ceramide backbone, making it zwitterionic with both positive (choline) and negative (phosphate) charges.
Galactocerebroside (B): This glycosphingolipid consists of a ceramide linked to a neutral galactose sugar residue, lacking any phosphate or charged groups, thus rendering it non-ionic and electrically neutral.
Lecithin (C): Lecithin, or phosphatidylcholine, has a zwitterionic phosphocholine headgroup on a diacylglycerol backbone, with opposing charges from phosphate and choline.
Phosphatidylinositol (D): This glycerophospholipid contains an inositol ring phosphorylated at multiple positions, resulting in a net negative charge due to multiple phosphate groups at physiological pH.
Which of the following lipids is non-ionic? This question tests core concepts in lipid biochemistry, distinguishing ionic phospholipids from neutral glycosphingolipids like galactocerebroside. Understanding ionic vs non-ionic lipids is essential for CSIR NET Life Sciences, as it relates to membrane structure, charge distribution, and signaling.
Lipid Structures and Charges
Lipids classify as ionic or non-ionic based on headgroup charge at physiological pH (~7.4). Phospholipids with phosphate typically carry net charge or zwitterionic properties, while neutral glycolipids do not.
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Sphingomyelin: Ceramide with phosphocholine; zwitterionic (net zero but polar).
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Galactocerebroside: Ceramide-galactose; fully neutral, no charges.
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Lecithin (Phosphatidylcholine): Glycerol with two fatty acids and phosphocholine; zwitterionic.
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Phosphatidylinositol: Glycerol backbone with phosphorylated inositol; anionic (negative charge).
Correct Answer: Galactocerebroside
Galactocerebroside stands out as non-ionic due to its uncharged galactose headgroup, unlike the phosphate-bearing options. It predominates in myelin sheaths, aiding compact membrane packing without electrostatic repulsion.
Biological Relevance
Non-ionic lipids like galactocerebroside promote myelin stability, while ionic ones like phosphatidylinositol drive signaling via charge interactions. For CSIR NET, note zwitterionic lipids (A, C) balance charges but remain “ionic” in context, contrasting true neutrals (B).
