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S-114 Chapter 10 Lipids
6. RS Designations for Alanine and Lactate Draw (using wedge-bond notation) and label the (R)
and (S) isomers of 2-aminopropanoic acid (alanine) and 2-hydroxypropanoic acid (lactic acid).
Answer 
2-Aminopropanoic acid
(alanine)
E E
E
C
H2N CH3
H
COOH
A
2-Hydroxypropanoic acid
(lactic acid)
E E
E
C
HO CH3
H
COOH
A
(R)-2-Aminopropanoic acid
COOH
CH
CH3
�
NH3
(S)-2-Aminopropanoic acid
COOH
C
CH3
H
�
H3N
(R)-2-Hydroxypropanoic acid (S)-2-Hydroxypropanoic acid
COOH
C
H
OHH3C
OH
C
H
COOHH3C
7. Hydrophobic and Hydrophilic Components of Membrane Lipids A common structural feature of
membrane lipids is their amphipathic nature. For example, in phosphatidylcholine, the two fatty acid
chains are hydrophobic and the phosphocholine head group is hydrophilic. For each of the following
membrane lipids, name the components that serve as the hydrophobic and hydrophilic units: (a) phos-
phatidylethanolamine; (b) sphingomyelin; (c) galactosylcerebroside; (d) ganglioside; (e) cholesterol.
Answer
Hydrophobic unit(s) Hydrophilic unit(s)
(a) 2 Fatty acids Phosphoethanolamine
(b) 1 Fatty acid and the hydrocarbon Phosphocholine
chain of sphingosine
(c) 1 Fatty acid and the hydrocarbon D-Galactose
chain of sphingosine
(d) 1 Fatty acid and the hydrocarbon Several sugar molecules
chain of sphingosine
(e) Steroid nucleus and acyl side chain Alcohol group
8. Structure of Omega-6 Fatty Acid Draw the structure of the omega-6 fatty acid 16:1.
Answer 
9. Catalytic Hydrogenation of Vegetable Oils Catalytic hydrogenation, used in the food industry, con-
verts double bonds in the fatty acids of the oil triacylglycerols to OCH2OCH2O. How does this affect the
physical properties of the oils?
Answer It reduces double bonds, which increases the melting point of lipids containing the 
fatty acids.
10. Alkali Lability of Triacylglycerols A common procedure for cleaning the grease trap in a sink is to
add a product that contains sodium hydroxide. Explain why this works.
O
�O
C
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