MLT GlobeChemistry: Lipids
107 Chemistry MCQs on Lipids with answers and explanations.
Triglycerides made in the liver are exported to muscle and adipose tissue mainly in:
Very-low-density lipoproteins carry endogenous triglyceride from the liver. Chylomicrons carry dietary (exogenous) fat from the gut.
Which of these fatty acids is a 16-carbon, rather than an 18-carbon, molecule?
Palmitate (16:0) is the end product of fatty acid synthase. Stearic (18:0), oleic (18:1) and linoleic (18:2) acids all have 18 carbons.
Triacylglycerols can be stored as anhydrous droplets in adipocytes because they are:
Esterification of all three glycerol hydroxyls removes charged groups, so TAGs are hydrophobic and stored without water, giving about 9 kcal/g.
A preterm infant with respiratory distress lacks dipalmitoylphosphatidylcholine in the alveoli. Chemically, this surfactant is a:
Dipalmitoyl lecithin is glycerol esterified with two palmitates and phosphocholine. It lowers alveolar surface tension; cerebrosides and gangliosides are sphingolipids.
Hydrolysis of lecithin releases glycerol, fatty acids, phosphate and which nitrogen-containing compound?
Lecithin is phosphatidylcholine. Ethanolamine is found in cephalin, serine in phosphatidylserine, and inositol (no nitrogen) in phosphatidylinositol.
Which compound is NOT derived from cholesterol?
Bilirubin comes from haem breakdown. Bile acids, steroid hormones and vitamin D3 are all formed from cholesterol.
Which fatty acid belongs to the omega-3 family?
α-Linolenic acid (18:3) has its last double bond three carbons from the methyl end. Linoleic and arachidonic acids are ω-6; palmitic acid is saturated.
Butter stored too long develops a sour odour as lipases release free fatty acids from triglycerides. This change is called:
Hydrolysis of ester bonds (often microbial lipase) frees volatile short-chain acids such as butyric acid. Oxidative rancidity involves peroxidation of double bonds.
Prostacyclin (PGI2), which inhibits platelet aggregation, is produced mainly by:
Endothelial prostacyclin synthase makes PGI2, which opposes platelet thromboxane A2 to keep vessels patent.
Which drug reduces prostaglandin formation by irreversibly acetylating cyclooxygenase?
Aspirin acetylates a serine in COX-1 and COX-2. Fluoride inhibits enolase and cyanide cytochrome oxidase.
According to current lipid guidelines, the desirable fasting serum total cholesterol for adults is:
Total cholesterol under 200 mg/dL (5.2 mmol/L) is desirable; 200–239 is borderline high and ≥240 mg/dL is high.
Nascent HDL particles are produced mainly by:
Hepatocytes and enterocytes secrete apoA-I-rich discoidal HDL that picks up cholesterol from tissues (reverse cholesterol transport).
An oil with a high iodine number is characterised by:
The iodine number is the grams of iodine absorbed per 100 g of fat, reflecting unsaturation. Rancidity is assessed by acid or peroxide values.
The VDRL and RPR tests for syphilis use which phospholipid as antigen?
Cardiolipin (diphosphatidylglycerol) is antigenic; antibodies to it (reagin) appear in syphilis and form the basis of non-treponemal tests.
β-Oxidation of palmitate takes place mainly in the:
Fatty acid oxidation occurs in the mitochondrial matrix in most tissues, yielding acetyl-CoA, NADH and FADH2. The cytosol is the site of fatty acid synthesis, which uses NADPH.
Which fatty acid is dietary-essential because humans cannot insert double bonds beyond carbon 9?
Linoleic acid (ω-6, C18:2) has a double bond at C-12 that human desaturases cannot create. Oleic acid is made from stearate by Δ9 desaturase; palmitic and stearic are saturated and synthesised.
Which animal-derived food is essentially free of cholesterol?
Egg cholesterol is concentrated in the yolk; albumen is almost pure protein and water. Milk and fish, being animal tissues or secretions, contain cholesterol.
Adipose tissue stores fuel mainly in the form of:
Triacylglycerols are anhydrous and energy-dense, making them the main fuel store. Free fatty acids are released during lipolysis; phospholipids are structural.
In hepatic steatosis (fatty liver), the lipid that accumulates in hepatocytes is mainly:
Fatty liver results when triacylglycerol synthesis exceeds export as VLDL, as in alcohol excess, obesity or choline deficiency. Other lipids are minor components.
The 'S' in the amniotic fluid L/S ratio is a choline-containing sphingolipid. It is:
Sphingomyelin contains phosphocholine attached to ceramide; lecithin (phosphatidylcholine) is the 'L'. Phosphatidylserine and phosphatidylethanolamine contain no choline.