Lipids: Basics MCQs

Ans. is 'd' i.e.,All of the above [Ref Vasudevan 6" p. 160] Metabolism of short chain fatty acids (SCFAs) and medium chain fatty acids (MCFAs) is drastically different from long chain fatty acids (LCFAs). SCFAs and MCFAs do not require pancreatic lipase and bile salts for digestion, but required for LCFAs digestion. SCFAs and MCFAs are directly absorbed from intestine into portal circulation, whereas LCFAs are taken by lymphatics, after incorporation into chylomicrons. SCFAs and MCFAs are oxidized by peripheral cells and are not used for storage. LCFAs are esterified with glycerol to form triacylglycerol, storage form of lipid

Explanation: Cardiolipin is a unique phospholipid present predominantly in the inner mitochondrial membrane . Functions: Maintains the structural integrity of mitochondria. Stabilizes and optimizes the activity of the electron transport chain (ETC) complexes and their supercomplexes. Structure & Synthesis: Has a distinctive dimeric structure with four fatty acid chains. Synthesized within mitochondria from phosphatidylglycerol and CDP-diacylglycerol (CDP-DAG) . Explanation of other options: Outer mitochondrial membrane (A): Mostly contains phosphatidylcholine & phosphatidylethanolamine, not cardiolipin. Cytosol (C): Cardiolipin is membrane-bound and absent in cytosol. Mitochondrial matrix (D): Not a membrane lipid, hence not present here.

Lecithin is a most abundant phospholipids of cell membrane not mitochondrial membrane. Lecithin (Phosphatidylcholine) Glycerophospholipid with Choline as nitrogenous base. i.e. Phosphatidic Acid + Choline. Most abundant phospholipid of cell membrane. Largest body store of choline. Importance of choline Acetylcholine in nerve transmission Transmethylation Dipalmitoyl Lecithin (Di Palmitoyl Phosphatidyl Choline) is a major constituent of lung surfactant. Reference: Harper's 32nd edition, page 216

In humans, the enzyme desaturase introduces double bonds to synthesize fatty acids and the human body has desaturases 9,6,5 and 4. The desaturase 9 introduces a double bond at carbons 9-10 and introducing double bonds beyond the 10 th carbon atom is not possible de novo. This is the reason why polyunsaturated acids ω-6 linoleic acid and ω-3 linolenic acid are essential fatty acids. Reference: LIPPINCOTT illustrated reviews 6 th edition page 188

Ans. is 'c' i.e., Methionine [Ref Essentials of biochemistry/p. 761] Lipotropic factors are substances which prevent accumulation of fat (TGs) in liver. Primary lipotropic factors choline, betaine, methionine, lecithine, inositol. Other factors with some lipotropic action :- Vitamin-13,2, folic acid, casein, glycine, essential fatty acids, selenium, vitamin E and serine.

Glycolipids or Glycosphingolipids Cerebroside Sulfatide Globoside Ganglioside Reference: Harper's 32nd edition, page 218

Ceramide = Sphingosine (Amino alcohol) + Fatty acid Ganglioside = Ceramide + Oligosaccharide that contains N Acetyl Neuraminic acid Cerebroside = Ceramide +Monosaccharide Sphingomyelin = Glycerol + 2 Fatty acid + PO4 + Choline. Reference: Harper's 32nd edition, page 218

Cervonic acid, also known as DHA, is an ω-3 fatty acid found in breast milk, fish oils and algal oil. Highest concentrations are in the retina, cerebral cortex and sperms. It is formed from α-Linolenic acid and NOT linoleic acid. It's deficiency is implicated in retinitis pigmentosa. Reference: LIPPINCOTT illustrated reviews 6 th edition page 363