Unit 24: Lipids
Fatty acids that pack together or refuse to, a triester that turns into soap, and one fused ring skeleton behind every steroid in the body.
4 topics · 12 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Fatty Acids and Saturation
- How it worksHow does a cis double bond put a rigid kink into a fatty acid's chain that keeps neighboring chains from packing tightly?
- Worked exampleFind whether oleic acid, with one cis double bond, or fully saturated stearic acid has the higher melting point.
- Going furtherWhat happens to a fat's melting point during industrial hydrogenation, when cis double bonds convert to trans ones instead of vanishing?
Your turn1 of 2
A fatty acid has 20 carbons total, including the carboxyl carbon, and 17 pairs of hydrogen atoms in its molecular formula. Given that the carboxyl group itself already accounts for one degree of unsaturation, how many carbon-carbon double bonds does this fatty acid contain?Triglycerides and Saponification
- How it worksHow does hydroxide attack each of a triglyceride's three ester bonds to release glycerol and three carboxylate soap molecules?
- Worked exampleFind the products formed when a triglyceride made from three glyceryl palmitate units is fully saponified with sodium hydroxide.
- Ties togetherHow does saponification reuse the exact same nucleophilic acyl substitution mechanism as base-catalyzed ester hydrolysis?
Your turn1 of 2
A sample contains 14.08 moles of a triglyceride. Full saponification with excess sodium hydroxide cleaves all three of its ester bonds. How many moles of sodium hydroxide are consumed?Phospholipids and the Cell Membrane
- How it worksHow does a phospholipid's polar phosphate head and nonpolar tails force it to face water on one side and hide from it on the other?
- Worked exampleFind how many fatty acid tails a typical phospholipid carries compared to the three carried by a triglyceride.
- Going furtherWhat happens to a lipid bilayer's fluidity when more of its fatty acid tails contain cis double bonds?
Your turn1 of 2
How many fatty acid tails does a typical phospholipid carry, compared to the three carried by a triglyceride?Steroids and the Terpene Skeleton
- How it worksHow does the body build every steroid from the same fused four-ring skeleton and then vary only the small groups attached to it?
- Worked exampleFind the number of carbon rings, and roughly how many are six-membered versus five-membered, in the core steroid skeleton.
- Going furtherWhat happens to a steroid's biological role when a single functional group, like a hydroxyl versus a ketone, changes on the ring?
Your turn1 of 2
How many carbon rings, and of what sizes, make up the core steroid skeleton?