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Chapter 10: Lipids
Terms in this set (30)
Which of the following statements concerning fatty acids is correct?
A) One is the precursor of prostaglandins.
B) Phosphatidic acid is a common one.
C) They all contain one or more double bonds.
D) They are a constituent of sterols.
E) They are strongly hydrophilic.
Which of the following molecules or substances contain, or are derived from, fatty acids?
E) All of the above contain or are derived from fatty acids.
Biological waxes are all:
A) trimesters of glycerol and palmitic acid.
B) esters of single fatty acids with long-chain alcohols.
C) trimesters of glycerol and three long chain saturated fatty acids.
E) none of the above.
Which of the following statements is true of lipids?
A) Many contain fatty acids in ester or amide linkage.
B) Most are simply polymers of isoprene.
C) Testosterone is an important sphingolipid found in myelin.
D) They are more soluble in water than in chloroform.
E) They play only passive roles as energy-storage molecules.
Which of the following contains an ether-linked alkyl group?
C) Phosphatidyl serine
D) Platelet-activating factor
Sphingosine is not a component of:
Which of the following statements about membrane lipids is true?
A) Glycerophospholipids are found only in the membranes of plant cells.
B) Glycerophospholipids contain fatty acids linked to glycerol through amide bonds.
C) Lecithin (phosphatidylcholine), which is used as an emulsifier in margarine and chocolate, is a sphingolipid.
D) Some sphingolipids include oligosaccharides in their structure.
E) Triacylglycerols are the principal components of erythrocyte membranes.
Which of the following is true of sphingolipids?
A) Cerebrosides and gangliosides are sphingolipids.
B) Phosphatidylcholine is a typical sphingolipid.
C) They always contain glycerol and fatty acids.
D) They contain two esterified fatty acids.
E) They may be charged, but are never amphipathic.
A compound containing N-acetylneuraminic acid (sialic acid) is:
B) ganglioside GM2.
D) platelet-activating factor.
Fatty acids are a component of:
D) vitamin D.
E) vitamin K.
Which of the following statements about sterols is true?
A) All sterols share a fused-ring structure with four rings.
B) Sterols are found in the membranes of all living cells.
C) Sterols are soluble in water, but less so in organic solvents such as chloroform.
D) Stigmasterol is the principal sterol in fungi.
E) The principal sterol of animal cells is ergosterol.
Which of the following is not true of sterols?
A) Cholesterol is a sterol that is commonly found in mammals.
B) They are commonly found in bacterial membranes.
C) They are more common in plasma membranes than in intracellular membranes (mitochondria, lysosomes, etc.).
D) They are precursors of steroid hormones.
E) They have a structure that includes four fused rings.
Which of the following best describes the cholesterol molecule?
B) Nonpolar, charged
C) Nonpolar, uncharged
D) Polar, charged
E) Polar, uncharged
Tay-Sachs disease is the result of a genetic defect in the metabolism of:
B) phosphatidyl ethanolamine.
E) vitamin D.
An example of a glycerophospholipid that is involved in cell signaling is:
A) arachidonic acid.
E) vitamin A (retinol).
Non-steroidal anti-inflammatory drugs (NSAIDS) like aspirin and ibuprofen act by blocking production of:
A) biological waxes
D) vitamin D
E) none of the above
Which of the following is not a fat-soluble vitamin?
Which vitamin is derived from cholesterol?
Identify the molecule(s) derived from sterols.
A) Arachidonic acid
E) Vitamin D
Circle the fatty acid in each pair that has the higher melting temperature.
(a) 18:19 18:29,12
(b) 18:0 18:19
(c) 18:0 16:0
Ans: (a) 18:19 (b) 18:0 (c) 18:0
Describe the dependence of the melting point of a fatty acid upon (a) chain length and (b) unsaturation; (c) explain these dependencies in molecular terms.
Ans: All other things being equal, (a) the longer the acyl chain, the higher the melting temperature; and (b) the more unsaturation, the lower the melting temperature. (c) The melting temperature is a measure of the thermal energy needed to break the intermolecular interactions that stabilize the "solid" form of a lipid, which depends upon how well the individual lipid molecules fit into the nearly crystalline array of lipids. When a shorter acyl chain lies between two longer chains in a nearly crystalline array of lipid molecules, there is a cavity at the end of the short acyl group that allows freer motion to the neighboring acyl chains. A cis double bond introduces a "kink" into the acyl chain, so that it does not pack as easily with its straighter neighbors.
What is the effect of a double bond on fatty acid structure?
Ans: Most double bonds in fatty acids are in the cis configuration. This results in a rigid bend in the hydrocarbon chain. (See Fig. 10-1, p. 345.)
In cells, fatty acids are stored as triacylglycerols for energy reserves. (a) What is the molecule to which fatty acids are esterified to form triacylglycerols? (b) Define the logic behind cells storing fatty acids in esterified form.
Ans: (a) Three fatty acids are esterified to glycerol. (b) Triacylglycerols are uncharged and insoluble in water. They form lipid droplets within adipocytes, which do not contribute to the osmolarity of the cytosol in those cells, and do not require any water of hydration.
What is the most significant chemical difference between triacylglycerols and glycerophospholipids that leads to their different functions?
Ans: Triacylglycerols are nonpolar hydrophobic molecules that can be stored in specialized nonaqueous cellular compartments. Glycerophospholipids are amphipathic molecules that can serve as structural components of membranes, which have hydrophilic and hydrophobic regions.
Describe three functions of triacylglycerols in mammals and one function in higher plants.
Ans: Triacylglycerols provide mammals with (1) stored fuel, (2) insulation, and (3) a source of metabolic water. In some animals, such as camels and desert rats, the oxidation of stored lipids provides water; in hibernating animals, oxidation of stored lipids generates heat to maintain body temperature (see Chapter 4). In plants, oxidation of the triacylglycerols stored in seeds provides the energy and precursors for biosynthetic processes during germination, before photosynthetic mechanisms become functional.
Show the basic structure of all glycerophospholipids.
Ans: All glycerophospholipids have two fatty acids in ester linkage with C-1 and C-2 of glycerol; often the fatty acid at C-1 is saturated, and that at C-2 is unsaturated. C-3 of glycerol is joined to an alcohol-containing head group through a phosphodiester linkage, which is negatively charged at neutral pH. (See Fig. 10-9, p. 351.)
Match the compounds on the left with the important roles they play listed on the right. (Answers are used only once.)
(a) prostaglandins ___ blood clotting
(b) sphingolipids ___ necessary for sight
(c) thromboxanes ___ mediates pain and inflammation
(d) vitamin A ___ important component of myelin membranes
Ans: c; d; a; b
Explain the cause of hereditary diseases of sphingolipid metabolism, such as Tay-Sachs and Niemann-Pick diseases.
Ans: These diseases are the result of mutations in the genes that code for enzymes of sphingolipid breakdown. The mutant enzyme is defective and unable to catalyze its reaction in the metabolic pathway; this results in the accumulation of the metabolic intermediate that is the substrate for the enzyme. (See Box 10-2, p. 356.)
Match each of these vitamins with its biological role: Vitamins A, D, E, K.
____ blood clotting
____ Ca2+ and phosphate metabolism
____ prevention of oxidative damage
Ans: K; A; D; E
Explain why extraction of lipids from tissues requires organic solvents.
Ans: Lipids are either strongly hydrophobic or amphipathic. Because the solvent in tissues is water, lipids are mainly present in aggregates. This aggregation does not occur in organic solvents; as a result, the lipids are more soluble and thus extractable from the tissues.
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