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Lehninger Principles of Biochemistry

David L. Nelson, Michael M. Cox

Chapter 10

Lipids - all with Video Answers

Educators

Chapter Questions

04:18

Problem 1

Operational Definition of Lipids How is the definition of "lipid" different from the types of definitions used for other biomolecules, such as amino acids, nucleic acids, and proteins?

Bryan Valdivia
Bryan Valdivia
Numerade Educator
03:55

Problem 2

Structure of an Omega-6 Fatty Acid Draw the structure of the omega-6 fatty acid 16: 1

Vishal Sharma
Vishal Sharma
Numerade Educator
04:53

Problem 3

Melting Points of Lipids The melting points of a series of 18 -carbon fatty acids are:
stearic acid, $69.6^{\circ} \mathrm{C} ;$ oleic acid, $13.4^{\circ} \mathrm{C} ;$ linoleic acid, $-5^{\circ} \mathrm{C} ;$ and linolenic acid, $-11^{\circ} \mathrm{C}$
(a) What structural aspect of these 18 -carbon fatty acids can be correlated with the melting point?
(b) Draw all the possible triacylglycerols that can be constructed from glycerol, palmitic acid, and oleic acid. Rank them in order of increasing melting point.
(c) Branched-chain fatty acids are found in some bacterial membrane lipids. Would their presence increase or decrease the fluidity of the membrane (that is, give the lipids a lower or higher melting point)? Why?

MK
Merly Konathapally
Numerade Educator
06:32

Problem 4

4. Catalytic Hydrogenation of Vegetable Oils Catalytic hydrogenation, used in the food industry, converts double bonds in the fatty acids of the oil triacylglycerols to $-\mathrm{CH}_{2}-$ $\mathrm{CH}_{2}-.$ How does this affect the physical properties of the oils?

Sana Riaz
Sana Riaz
Numerade Educator
03:03

Problem 5

Impermeability of Waxes What property of the waxy cuticles that cover plant leaves makes the cuticles impermeable to water?

Vasu Makani
Vasu Makani
Numerade Educator
04:30

Problem 6

Naming Lipid Stereoisomers The two compounds below are stereoisomers of carvone with quite different properties; the one on the left smells like spearmint, and that on the right, like caraway. Name the compounds using the RS system.

Sana Riaz
Sana Riaz
Numerade Educator
01:43

Problem 7

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).

Hailey Tomashek
Hailey Tomashek
Numerade Educator
04:06

Problem 8

8. 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)phosphatidylethanolamine;
(b) sphingomyelin;
(c) galactosylcerebroside;
(d) ganglioside;
(e) cholesterol.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
01:21

Problem 9

Deducing Lipid Structure from Composition Compositional analysis of a certain lipid shows that it has exactly one mole of fatty acid per mole of inorganic phosphate. Could this be a glycerophospholipid? A ganglioside? A sphingomyelin?

Matthew Wither
Matthew Wither
Numerade Educator
04:52

Problem 10

Deducing Lipid Structure from Molar Ratio of Components Complete hydrolysis of a glycerophospholipid yields glycerol, two fatty acids $\left(16: 1\left(\Delta^{9}\right) \text { and } 16: 0\right),$ phosphoric acid, and serine in the molar ratio $1: 1: 1: 1: 1 .$ Name this lipid and draw its structure.

Mackenzie Voots
Mackenzie Voots
Numerade Educator
04:57

Problem 11

Lipids in Blood Group Determination We note in Figure $10-14$ that the structure of glycosphingolipids determines the blood groups $A, B,$ and $O$ in humans. It is also true that glycoproteins determine blood groups. How can both statements be true?

Sana Riaz
Sana Riaz
Numerade Educator
08:17

Problem 12

The Action of Phospholipases The venom of the Eastern diamondback rattler and the Indian cobra contains phospholipase $\mathrm{A}_{2},$ which catalyzes the hydrolysis of fatty acids at the $C-2$ position of glycerophospholipids. The phospholipid breakdown product of this reaction is lysolecithin (lecithin is phosphatidylcholine). At high concentrations, this and other lysophospholipids act as detergents, dissolving the membranes of erythrocytes and lysing the cells. Extensive hemolysis may be lifethreatening.
(a) All detergents are amphipathic. What are the hydrophilic and hydrophobic portions of lysolecithin?
(b) The pain and inflammation caused by a snake bite can be treated with certain steroids. What is the basis of this treatment?
(c) Though the high levels of phospholipase $A_{2}$ in venom can be deadly, this enzyme is necessary for a variety of normal metabolic processes. What are these processes?

Sana Riaz
Sana Riaz
Numerade Educator
05:05

Problem 13

Intracellular Messengers from Phosphatidylinositols When the hormone vasopressin stimulates cleavage of $\mathrm{PIP}_{2}$ by phospholipase $\mathrm{C}$, two products are formed. What are they?
Compare their properties and their solubilities in water, and predict whether either would diffuse readily through the cytosol.

Sana Riaz
Sana Riaz
Numerade Educator
07:25

Problem 14

Isoprene Units in Isoprenoids Geraniol, farnesol, and squalene are called isoprenoids because they are synthesized from five-carbon isoprene units. In each compound, circle the five-carbon units representing isoprene units (see Fig. $10-22$ ).

Sydney Atkins
Sydney Atkins
Numerade Educator
03:24

Problem 15

Hydrolysis of Lipids Name the products of mild hydrolysis with dilute $\mathrm{NaOH}$ of $(\mathrm{a}) 1-$ stearoyl-2,3-dipalmitoylglycerol;
(b) 1 -palmitoyl-2-oleoylphosphatidylcholine.

Ronald Prasad
Ronald Prasad
Numerade Educator
03:53

Problem 16

Effect of Polarity on Solubility Rank the following in order of increasing solubility in water: a triacylglycerol, a diacylglycerol, and a monoacylglycerol, all containing only palmitic acid.

DA
David Alaniz
Numerade Educator
04:35

Problem 17

Chromatographic Separation of Lipids A mixture of lipids is applied to a silica gel column, and the column is then washed with increasingly polar solvents. The mixture consists of phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, cholesteryl palmitate (a sterol ester), sphingomyelin, palmitate, $n$ -tetradecanol, triacylglycerol, and cholesterol. In what order will the lipids elute from the column? Explain your reasoning.

Rashmi Sinha
Rashmi Sinha
Numerade Educator
05:44

Problem 18

Identification of Unknown Lipids Johann Thudichum, who practiced medicine in London about 100 years ago, also dabbled in lipid chemistry in his spare time. He isolated a variety of lipids from neural tissue and characterized and named many of them. His carefully sealed and labeled vials of isolated lipids were rediscovered many years later.
(a) How would you confirm, using techniques not available to Thudichum, that the vials labeled "sphingomyelin" and "cerebroside" actually contain these compounds?
(b) How would you distinguish sphingomyelin from phosphatidylcholine by chemical, physical, or enzymatic tests?

Sana Riaz
Sana Riaz
Numerade Educator
03:41

Problem 19

Ninhydrin to Detect Lipids on TLC Plates Ninhydrin reacts specifically with primary amines to form a purplish-blue product. A thin-layer chromatogram of rat liver phospholipids is sprayed with ninhydrin, and the color is allowed to develop. Which phospholipids can be detected in this way?

Sana Riaz
Sana Riaz
Numerade Educator
03:30

Problem 20

Determining the Structure of the Abnormal Lipid in Tay-Sachs Disease Box $10-1$, Figure $1,$ shows the pathway of breakdown of gangliosides in healthy (normal) individuals and in individuals with certain genetic diseases. Some of the data on which the figure is based were presented in a paper by Lars Svennerholm (1962). Note that the sugar Neu5Ac, $N$ -acetylneuraminic acid, represented in the Box 10 -1 figure as

Svennerholm reported that "about $90 \%$ of the monosialogangliosides isolated from normal human brain" consisted of a compound with ceramide, hexose, $N$ acetylgalactosamine, and $N$ -acetylneuraminic acid in the molar ratio 1: 3: 1: 1
(a) Which of the gangliosides (GM1 through GM3 and globoside) in Box $10-1$, Figure
1, fits this description? Explain your reasoning.
(b) Svennerholm reported that $90 \%$ of the gangliosides from a patient with Tay-Sachs had a molar ratio (of the same four components given above) of $1: 2: 1: 1 .$ Is this consistent with the Box 10 - 1 figure? Explain your reasoning.

To determine the structure in more detail, Svennerholm treated the gangliosides with neuraminidase to remove the $N$ -acetylneuraminic acid. This resulted in asialoganglioside that was much easier to analyze. He hydrolyzed it with acid, collected the ceramide-containing products, and determined the molar ratio of the sugars in each product. He did this for both the normal and the Tay-Sachs gangliosides. His results are shown below.
$$\begin{array}{lccc}
\text { Ganglioside CeramideGlucose Galactose Galactosamine } & & \\
\hline \text {Normal} & & & \\
\text { Fragment 1 } & 1 & 1 & 0 & 0 \\
\text { Fragment 2 } & 1 & 1 & 1 & 0 \\
\text { Fragment 3 } & 1 & 1 & 1 & 1 \\
\text { Fragment 4 } & 1 & 1 & 2 & 1 \\
\text {Tay-Sachs} & & & & \\
\text { Fragment 1 } & 1 & 1 & 0 & 0 \\
\text { Fragment 2 } & 1 & 1 & 1 & 0 \\
\text { Fragment 3 } & 1 & 1 & 1 & 1 \\
\hline
\end{array}$$
(c) Based on these data, what can you conclude about the structure of the normal ganglioside? Is this consistent with the structure in Box 10 -1? Explain your reasoning.
(d) What can you conclude about the structure of the Tay-Sachs ganglioside? Is this consistent with the structure in Box 10 -1? Explain your reasoning.

Svennerholm also reported the work of other researchers who "permethylated" the normal asialoganglioside. Permethylation is the same as exhaustive methylation: a methyl group is added to every free hydroxyl group on a sugar. They found the following permethylated sugars: 2,3,6 -trimethylglycopyranose; 2,3,4,6 -tetramethylgalactopyranose; 2,4,6 -trimethylgalactopyranose; and 4,6 -dimethyl-2-deoxy-2-aminogalactopyranose.
(e) To which sugar of GM1 does each of the permethylated sugars correspond? Explain your reasoning.
(f) Based on all the data presented so far, what pieces of information about normal ganglioside structure are missing?

Sana Riaz
Sana Riaz
Numerade Educator