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Chapter 27: Biomolecules: Lipids

Every problem in the chapter beside the book’s answer, a chapter at a time as you scroll.

Chapter 27: Biomolecules: Lipids

10 problems · 14 figures

27-1 §27.1 source ↗

Carnauba wax, used in floor and furniture polishes, contains an ester of a C32 straight-chain alcohol with a C20 straight-chain carboxylic acid. Draw its structure.

Answer

CH3(CH2)18CO2CH2(CH2)30CH3

27-2 §27.1 source ↗

Draw structures of glyceryl tripalmitate and glyceryl trioleate. Which would you expect to have a higher melting point?

Answer

Glyceryl tripalmitate is higher melting.

27-3 §27.2 source ↗

Draw the structure of magnesium oleate, a component of bathtub scum.

Answer

[ C H 3 ( C H 2 ) 7 C H ═ C H ( C H 2 ) 7 C O 2 − ] 2   M g 2 +

27-4 §27.2 source ↗

Write the saponification reaction of glyceryl dioleate monopalmitate with aqueous NaOH.

Answer

Glyceryl dioleate monopalmitate → glycerol + 2 sodium oleate + sodium palmitate

27-5 §27.4 source ↗

Assign R or S configuration to each chirality center in prostaglandin E2 (Figure 27.6), the most abundant and biologically potent of mammalian prostaglandins.
Figure 27.6 in the book ↗
Mechanism of the conversion of PGH2 into PGE2.

Answer

27-6 §27.5 source ↗

The conversion of mevalonate 5-phosphate to isopentenyl diphosphate occurs with the following result. Which hydrogen, pro-R or pro-S, ends up cis to the methyl group, and which ends up trans?

Answer

The pro-S hydrogen is cis to the −CH3 group; the pro-R hydrogen is trans.

27-7 §27.5 source ↗

Propose mechanistic pathways for the biosynthetic formation of the following terpenoids:
(a)
(b)

Answer (2 parts)

(a)
(b)

27-8 §27.6 source ↗

Draw the following molecules in chair conformations, and tell whether the ring substituents are axial or equatorial:
(a)
(b)

Answer (2 parts)

(a)
(b)

27-9 §27.6 source ↗

Lithocholic acid is an A–B cis steroid found in human bile. Draw lithocholic acid showing chair conformations, as in Figure 27.12, and tell whether the hydroxyl group at C3 is axial or equatorial.
Figure 27.12 in the book ↗
Steroid conformations. The three 6-membered rings have chair conformations but are unable to undergo ring-flips. The A and B rings can be either cis-fused or trans-fused.

Answer

27-10 §27.7 source ↗

Compare the structures of lanosterol and cholesterol, and catalog the changes needed for the transformation shown.

Answer

Three methyl groups are removed, the side-chain double bond is reduced, and the double bond in the B ring is migrated.

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Problems and answers are adapted from Organic Chemistry: A Tenth Edition by John McMurry, OpenStax, and are used under the CC BY-NC-SA 4.0 licence. Access for free at https://openstax.org/books/organic-chemistry/pages/1-why-this-chapter. Illustrations: Copyright Rice University, OpenStax, under CC BY-NC-SA 4.0 license. This adaptation is released under the same licence, is non-commercial, and is neither affiliated with nor endorsed by OpenStax or Rice University.