Chap. 10. Problem 2. Part (a). The melting points of
fatty acids are strongly
influenced by the number of cis
double bonds present in the
fatty acid acyl chain. Cis
double bonds cause acyl chains
to adopt a kinked (bent)
conformation in a crystal
lattice, and the poorer packing
(relative to straight acyl
chains) decreases melting point.
This explains the decline in the melting points of the 18-carbon
fatty acids series listed above (# of double bonds: stearic acid,
18:0; oleic acid, 18:1; linoleic acid, 18:2; linolenic acid, 18:3).
Part (b). There are six possible triacylglycerols that can occur.
These can be represented as OOO, OOP, OPO, POP, OPP, & PPP,
based on the fatty acids attached to the glycerol backbone.
Because the melting point of oleic acid (O) is less than palmitic
acid (P), the order of their melting points (from low-to-high) is
OOO < OOP = OPO < POP = OPP < PPP.
Part (c). Branched-chain fatty acids do not pack as well as
straight-chain species and thus have lower melting points and
impart greater fluidity to membranes.
Chap. 10. Problem 4.
The five-carbon isoprene units
in geraniol, farnesol, and
squalene are circled in the
diagram.
Chap. 10. Problem 7.
Hydrophobic Units
Hydrophilic Units
a. 2 fatty acids
phosphoethanolamine
b. 1 fatty acid +
sphingosine
phosphocholine
c. 1 fatty acid +
sphingosine
D-galactose
d. 1 fatty acid +
sphingosine
oligosaccharide head
group
e. steroid nucleus +
alkyl side chain
hydroxyl group at
position-3
Chap. 10. Problem 10.
Grease produced by cooking is predominantly animal fat consisting
of triacylglycerols. The ester linkages in triacylglycerols are
readily hydrolyzed by treatment with strong base (e.g., sodium
hydroxide). Treatment with strong base produces glycerol and 3
fatty acids from a triacylglycerol. These hydrolysis products are
much more soluble in water than triacylglycerols themselves. The
cleavage products can be washed away with water.
Chap. 10. Problem 16.
The two products produced by phospholipase C cleavage of
phosphatidyl 4,5-bisphosphate are diacylglycerol and inositol
1,4,5-trisphosphate (IP3). Both of these cleavage products are
second messengers that activate intracellular pathways used in
vasopressin signaling (Chap. 12). Diacylglycerol is a hydrophobic
lipid that remains in the cytoplasmic membrane in which the
cleavage event occurs. IP3, on the other hand, is very polar and is
released into the cytoplasm of the cell.
Chap. 10. Problem 17.
Water-soluble vitamins are subject to excretion by the kidneys
on a daily basis. Fat-soluble vitamins (A, D, E, K) are lipidsoluble and thus partition into fat stores in body tissues. These
tissues therefore provide a reservoir of fat-soluble vitamins that
can serve the individual for months.
Chap. 10. Problem 20.
Silica gel is a polar matrix than binds polar lipids more strongly
than nonpolar lipids. Thus nonpolar lipids will elute from a silica gel
column earlier than polar lipids. Based on consideration of the
hydrophobic-hydrophilic balance for the mentioned lipids,
cholesteryl palmitate and triacylglycerol should elute from the
column first. Cholesterol and n-tetradecanol being somewhat more
polar due to their free hydroxyl groups would elute next. The
neutral phospholipids phosphatidylcholine and
phosphatidylethanolamine would then elute, followed by
sphingomyelin, which has a slightly greater content of polar
functional groups. Finally, the negatively charged
phosphatidylserine and palmitate would elute from the column. Of
these two lipids phosphatidylserine would elute first because it has
a lower charge-to-mass ratio than palmitate.