MLT GlobeChemistry: Lipids – page 3
107 Chemistry MCQs on Lipids with answers and explanations.
In enzymatic triglyceride methods, triglycerides are first hydrolysed by which enzyme?
Lipase hydrolyses triglycerides to glycerol and free fatty acids; the glycerol is then measured through glycerol kinase and further coupled reactions.
Which lipoprotein carries dietary (exogenous) triglyceride from the intestine into the blood?
Chylomicrons are made by intestinal cells from absorbed dietary fat and carry it via the lymph into the blood. VLDL carries triglyceride made in the liver.
Lipoprotein lipase on capillary walls hydrolyses the triglyceride carried in which lipoproteins?
Lipoprotein lipase, activated by apo C-II, removes triglyceride from the triglyceride-rich lipoproteins, chylomicrons and VLDL. LDL and HDL are cholesterol-rich.
Hormone-triggered release of IP3 and DAG, and membrane events such as exocytosis, depend on which membrane phospholipid?
Phospholipase C cleaves phosphatidylinositol 4,5-bisphosphate into IP3 and DAG; phosphoinositides also regulate vesicle trafficking. Phosphatidylglycerol is mainly a cardiolipin precursor.
The key cholesterol-synthesis intermediate HMG-CoA contains an acyl group of how many carbon atoms?
3-Hydroxy-3-methylglutaryl is a five-carbon glutaryl chain plus a methyl branch: six carbons, formed from acetyl-CoA plus acetoacetyl-CoA (2 + 4).
Which lipid is a glycerol-based ether phospholipid lacking sphingosine?
Plasmalogens have a vinyl-ether link at glycerol C1. Sphingomyelin, cerebrosides and gangliosides are built on sphingosine.
Which statement about fatty acids is correct?
Arachidonate is formed by elongation and desaturation of linoleate, so it is only conditionally essential. Natural unsaturated fatty acids are cis, and unsaturation lowers melting point.
Glycerol serves as a backbone or substrate for all of these EXCEPT:
Glycosphingolipids such as cerebrosides are built on sphingosine. Glycerol-3-phosphate forms TAGs and phospholipids, and the liver converts glycerol to glucose.
Which fatty acid has 16 carbons and a single cis double bond (16:1 Δ9)?
Palmitoleic acid is 16:1. Oleic is 18:1 cis, elaidic is its trans isomer, and erucic is 22:1.
Which drug lowers leukotriene production without inhibiting cyclooxygenase?
Zileuton blocks 5-lipoxygenase, the leukotriene pathway, and is used in asthma. Ibuprofen, indomethacin and aspirin are COX inhibitors.
Cholera toxin binds intestinal cells through which membrane glycolipid receptor?
The B subunit binds GM1, allowing the A subunit to enter and ADP-ribosylate Gs, raising cAMP and causing watery diarrhoea.
Ceramide, the parent of all sphingolipids, consists of:
A fatty acid in amide linkage to sphingosine forms ceramide. Adding phosphocholine gives sphingomyelin; adding sugars gives glycosphingolipids.
After LDL is taken into a cell by receptor-mediated endocytosis, its cholesteryl esters are hydrolysed in the:
Endosomes fuse with lysosomes, where acid lipase frees cholesterol. The ER is where free cholesterol is later re-esterified by ACAT and where it regulates HMG-CoA reductase.
The sugar most often attached to ceramide in cerebrosides of brain myelin is:
Galactocerebroside is the main cerebroside of neural myelin. Glucocerebroside dominates outside the nervous system, and sialic acid characterises gangliosides.
Which phospholipid is concentrated mainly in the outer (extracellular) leaflet of the plasma membrane?
Choline phospholipids (phosphatidylcholine, sphingomyelin) face outward. Phosphatidylserine is kept on the inner leaflet; its exposure outside signals apoptosis and supports coagulation.
Which movement of phospholipids in a bilayer is very slow unless catalysed by flippase-type enzymes?
Moving the polar head group through the hydrophobic core is energetically unfavourable, so spontaneous flip-flop is rare. Lateral diffusion, rotation and chain flexing occur rapidly.
Which property of cholesterol accounts for its stiffening effect on the membrane bilayer?
The flat fused rings restrict movement of neighbouring acyl chains. Membrane cholesterol is mostly unesterified, with its hydroxyl near the phospholipid head groups and its tail buried in the core.
Long-chain fatty acyl groups cross the inner mitochondrial membrane for β-oxidation by means of the:
CPT-I forms acylcarnitine, a translocase carries it across, and CPT-II regenerates acyl-CoA in the matrix. The citrate shuttle exports acetyl units for fatty acid synthesis; malate–aspartate moves NADH equivalents.
Palmitate (C16:0) released by fatty acid synthase is elongated in the endoplasmic reticulum mainly to:
Microsomal elongases add two-carbon units from malonyl-CoA, converting palmitate to stearate. Linoleic and α-linolenic acids are essential, and EPA is made from α-linolenate, not palmitate.
Which metabolite inhibits carnitine palmitoyltransferase-I, preventing newly made fatty acids from being oxidised?
Malonyl-CoA, the first committed intermediate of fatty acid synthesis, blocks CPT-I so synthesis and oxidation do not run together. Acetyl-CoA is a substrate, not the CPT-I inhibitor.