Practice Problems on Lipids

Transcription

1 Lipids.1 Practice Problems on Lipids 1. Which one of the following compounds has the structural pattern of the naturally occurring fats or oils? a) b) c) d) e) Which of the following compounds is least likely to be a natural fatty acid? a) b) c) d) e)

2 Lipids.2 3. Which of the following compounds is most likely to be a solid?

3 Lipids.3 4. Which of the following fatty acids is least likely to be found in a natural fat or oil? 5. Which of the following is most likely a natural fatty acid?

4 Lipids.4 6. Which of the following mechanistic steps are not part of the mechanism for the laisen condensation of methyl acetate ( 3 3 in 3 a/methanol)? I II III IV ) II ) III and IV ) II and III ) I and IV ) I and II

5 Lipids.5 7. Which one of the following is the normal product of the reaction sequence catalyzed by the fatty acid synthetase complex? a) S P b) S P c) S P d) S P e) S P 8. Which one of the following compounds would not be an intermediate in the biochemical synthesis of the compound below? SP SP SP SP SP

6 Lipids.6 9. Which one of the following is least likely to be involved in the biosynthesis of palmitic acid? SP SFS SP SP SP 10. Which one of the following processes is most likely to be involved in the mechanism of fatty acid synthase? In all cases "" or "" are part of an enzyme active site, and "R" is the rest of P 3 SP 3 SP 2 3 R 2 R SP SP SP R

7 Lipids Which one of the correctly shows the mechanism of a Michael ddition? ) u ) 2 ) u ) ) 12. When P acts as a reducing agent, which is transferred to the compound being reduced? (ircle correct ) 2 P 2 2 P 2

8 Lipids In fatty-acid biosynthesis, acetyl o is converted into malonyl o. Why is malonyl o synthesized? ) To incorporate another carbon from 2 into the growing chain ) To provide a catalytic group able to act as a base ) To make the laisen step favour product formation ) To make malonyl o more soluble in water ) To make malonyl o bind more strongly to fatty acid synthetase 14. To convert acetyl-o into 3 -( 2 ) 14 --S-R, how many equivalents of P must the cell use per equivalent of product formed? (Work out answer) 15. In nature, biotin is used as a: ) Reducing agent ) ehydrating agent ) arbonyl transfer agent ) xidizing agent ) ydrating agent

9 Lipids Palmitic acid with the carbon atoms numbered is shown below. Which - bond is formed by the laisen condensation between butyryl thiolester (a 4 carbon electrophile) and malonyl-p? ) ) 8 9 ) ) ) utanoic acid is biosynthesized by a route identical to the fatty acid biosynthetic pathway. If, during the biosynthesis of butanoic acid, all of the starting material (acetyl o) is isotope labelled at the methyl carbon atom as indicated by the asterisk, which atom(s) will be labelled in the product? ssume that the only organic carbon source is acetyl o. 3 * So 3 I II III IV ) I and III only ) I and II only ) II and IV only ) II and III only ) I only

10 Lipids Which one of the following compounds will most likely form micelles in water? a S 3 a S 3 a 19. Which one of the following would not act as a soap or detergent? ( 3 ) 3 l S 3 a a

11 Lipids arly settlers in anada prepared soap by boiling animal fat with wood ashes, a source of a and K. This technique can be seen at the Lower Fort Garry ational istoric Site in Manitoba. Which one of the following statements about this soap-making process is T correct? ) This process is called saponification ) fter the hydrolysis the soap is precipitated by al ) Soap made this way give precipitates with hard water ) Soaps made this way contain phosphates that bind metal ions ) Soaps made this way are readily biodegradable 21. ow many of the following are soluble in water? 3 ( 2 ) ( 2 ) 16 2 K [ 3 ( 2 ) 4 =( 2 ) 7 2 ] 2 a 2 ( 2 ) 14 3 ( 2 ) 14 3 [ 3 ( 2 ) 12 2 S 3 ] 2 Mg 2 ( 2 ) Which one of the following is not an effective cleaning agent? 2 Mg 2+ S 3 2 a2+ K a S 3 a

12 Lipids Which one of the following detergents would not be a good laundry product when used with hard water? S 3 a S 3 a 2 a S 3 a S 3 a 24. Which one of the following is not likely to be a useful part of a detergent formulation? a) b) c) 2 P Si P P Si Si 2 2 d) e)

13 Lipids uring the synthesis of an alkylbenzenesulfonate detergent, the following transformation below is made. Which of 1-5 are involved in the correct mechanism? ) nly 2 and 3 ) nly 1 and 4 ) nly 2, 3, and 5 ) nly 1, 4, and 5 ) ll of the steps are involved

14 Lipids Which chemical step is least likely to occur? S 3 S 3 ) S 3 S 3 ) 2 2 S 3 S 3 ) 3 3 S 3 S 3 ) S 3 S 3 )

15 Lipids The following polymer can be synthesized by the acid-catalyzed polymerization of which building block? * * ) ) ) ) ) 28. Which one of the following is not biodegradable? S 3 a S 3 a ( 3 ) 3 l 2 a

16 Lipids Which one of the following statements best describes why phospholipids form bilayers whereas the metal salts of fatty acids form micelles in aqueous solution ) The aggregates formed in aqueous solution reflect a balance between maximizing the electrostatic attraction of the head groups and minimizing the contact of the lipophilic tail groups ) The repulsion between water and the tail groups of the metal salts of fatty acids is minimized in a micellular structure ) The aggregates formed in aqueous solution reflect a balance between maximizing hydrogen bonding between the head groups and maximizing the contact between the lipophilic tail groups. ) The aggregates formed in aqueous solution reflect a balance between minimizing the electrostatic replusion of the head groups and maximizing the contact of the lipophilic tail groups ) The electrostatic repulsion between the ionic head groups of metal salts of fatty acids is maximized in a micellular structure 30. PGF (shown below) is an extremely important prostaglandin that stimulates the contraction of smooth muscles. Which of the oxygen atoms in PGF from the cyclooxygenase-catalyzed reaction using oxygen molecules from the air? a e d b c ) a and b only ) a, b, and c only ) e and d only ) a and c only ) all except for e

17 Lipids Which one of the following statements about prostaglandins is incorrect? ) ccolate and Singular interfere with the action of prostaglandins. ) Vioxx, elebrex, and extra all inhibit the oxidation of arachidonic acid. ) Many prostaglandins are inflammatory agents. ) The enzymatic oxidation of arachidonic acid forms a 5-membered ring. ) Prostaglandins are synthesized primarily in the prostate gland. 32. Which one of the lipids would not be found as part of a biological membrane? 2 2 P P 2 2 ( 3 ) 3 l P 2 2 ( 3 ) 3 l

18 Lipids Which one of the following will form a bilayer by itself? P ( 3 ) 3 3 P ( 3 ) Which one of the following statements is not correct? ) The first step of prostaglandin synthesis from arachidonic acid involves the formation of a cyclopentane ring by the enzyme cyclooxygenase. ) Phospholipid bilayers are leaky and compounds can easily pass unassisted through the bilayer. ) In electrophilic aromatic substitution, electron-donating substituents on the aromatic ring are ortho/para directors. ) Phosphate compounds can be added to detergents to increase their performance in hard water. ) Micelles have a hydrophobic interior.

19 Lipids Which one of the following is not a terpene? 36. Which one of the following is not a terpene? a) b) c) d) e)

20 Lipids Which one of the following is not a terpene? 38. The enzyme catalyzed reaction between dimethylallyl pyrophosphate and isopentenyl pyrophosphate to give geranyl pyrophosphate is shown below. Which of the following arrows indicate where there is a significant build up of positive charge during the reaction? V 3 3 P 2 6 P 2 6 III IV isopentenyl pyrophosphate geranyl pyrophosphate P I II dimethylallyl pyrophosphate ) t carbons I, III, and V ) t carbons I, II, and V ) t carbons II and IV ) t carbons I, II, and V ) t carbons III and IV

21 Lipids Which compound is a terpene, based on obeying the isoprene rules? ) ) isohumulone - bitter tasting and found in beer bulnesol ) ) ( 2 ) 4 3 iso-germacrene tetrahydrocannabinol - found in plants ) humulone - from hops and found in beer

22 Lipids Terpenes are biosynthesized from dimethylallyl pyrophosphate and isopentenyl pyrophosphate. escribe, in words, and by writing a mechanism, how these two molecules are linked together to form geranyl pyrophosphate. PP imethylallyl pyrophosphate PP Isopentenyl pyrophosphate Geranyl pyrophosphate 41. Which one of the following carbon-carbon linkages was most likely to have been formed by a reductive dimerization reaction? 42. The reaction step shown occurs during the biosynthesis of terpenes and steroids. Which one of statements is correct? 3 nzyme 3 SR SR 2 SR ) The two thioester groups in the starting material differ in chemical reactivity. ) Production of a single enantiomer from an achiral starting material requires a chiral catalyst. ) The product retains a plane of symmetry. ) This reaction requires P. ) The carbonyl carbon of the remaining thiolester will subsequently be reduced and removed.

23 Lipids Which one of the following molecules is involved in terpene biosynthesis? P 2 P 3 P 2 P 3 P 2 P 3 P 2 P 3 P 2 P alculate the number of moles of TP needed to synthesize one mole of dimethylallyl pyrophosphate from three moles of acetyl o.

24 Lipids The tail of chlorophyll is comprised of a terpene alcohol, phytol. Phytol can be biosynthesized exclusively from acetyl o tagged with carbon-13 isotope as the carboxyl carbon atom and carbon-14 isotope as the methyl carbon atom, as shown on the right So Which one of shows phytol with the correct placement of atoms? The red colour of tomatoes is attributed to the antioxidant lycopene, the consumption of which has been suggested to reduce the risk of certain cancers. ow many head-to-tail linkages of the isoprene building block are present in lycopene, a 40 tetraterpene? ) 5 ) 3 ) 4 ) 7 ) 6

25 Lipids uring the synthesis of mevalonic acid, the reaction below takes place. Which one of statements is not correct? 3 2 SR + 3 SR 3 2 SR 2 SR ) This aldol reaction is the result of a nucleophilic attack by the enolate of the acetylthiolester on a -ketothiolester. ) The enolate of the acetylthiolester attacks the keto carbonyl rather than the thiolester carbonyl because the thiolester carbonyl is less electrophilic. ) This enzyme-catalyzed reaction results in the formation of only one enantiomer. ) It is not necessary to generate the enolate of the acetylthiolester by a decarboxylation since the thermodynamics of the aldol reaction are favourable. ) The -ketothiolester (the starting material) was formed in a modified laisen condensation between an acetyl thiolester and a malonyl thiolester. 48. Which one of the following is not a steroid? 2 a b c d e all are steroids

26 Lipids Which one of the following represents the folding of squalene oxide that is used for the enzyme-catalyzed cyclization to lanosterol? 50. holesterol is biosynthesized from the triterpene squalene, which has a single tail-to-tail (T-T) connection. Which bond in cholesterol corresponds to that T-T bond originally present in squalene? 51. Which one of the following compounds is least likely to be involved in the biosynthesis of cholesterol? P P P P P

27 Lipids Squalene epoxide is converted to lanosterol by two major processes. The first process is the carbon-carbon bond-forming reactions which form the characteristic steroid ring structure. The second process involves group and atom migrations and the elimination of a proton ultimately giving lanosterol. With respect to the first process only (the cyclization reactions), which atoms would bear some positive charge (even temporarily)? ) 1, 2, 3, 4, 5 ) 1, 9, 3, 4, 6 ) 1, 2, 3, 7 ) 10, 9, 2, 3, 8, 4 ) 10, 2, 8, 7 1

28 Lipids uring the biosynthesis of cholesterol, squalene oxide is converted to lanosterol as shown below. otice that one of the methyl groups in squalene oxide has been labeled with a star. Which one of the following methyl groups in lanosterol originated as the labeled methyl group in squalene oxide? squalene oxide lanosterol 54. Which one of the following statements about vitamin is not correct? ) Vitamin can form a resonance stabilized radical. ) Vitamin can form a hindered radical. ) Vitamin is a fat-soluble vitamin. ) Molecules with similar structural features as vitamin are used as antioxidants (preservatives) in foodstuffs. ) Vitamin is a triterpene.

29 Lipids Which one of the following statements is T correct? ) Vitamin is a fat-soluble vitamin. ) Vitamin K is required for the coagulation of blood. ) Polar bears store large amounts of Vitamin in their liver. ) Vitamin is a cholesterol derivative. ) The biosynthesis of vitamin requires light. 56. Which one of the following compounds would not be classified as a lipid? ( 3 ) P

30 Lipids Which one of the following steps is consistent with a nucleophilic acyl substitution mechanism? ) S S ) So So So So ) So So So So l l l l ) l 2 -R l 2 -R ) 2 2

31 Lipids The sequence of events listed below corresponds to which reaction mechanism? 1. Protonation of sp 2 oxygen 2. ucleophilic attack and formation of tetrahedral intermediate 3. Proton transfer 4. ollapse of tetrahedral intermediate, regeneration of sp 2 oxygen, and loss of leaving group 5. eprotonation ) lectrophilic aromatic substitution ) cid-catalyzed nucleophilic addition ) Saponification ) S 1 substitution ) cid-catalyzed nucleophilic acyl substitution 59. When detergents are dissolved in water, the p of the resulting solution is close to neutral, while soap solutions are alkaline. Which statement best explains this phenomenon? ) etergents contain less unsaturation than soaps. ) etergents are typically salts of strong acids. ) Soaps precipitate in the presence of a 2+. ) Soaps are carboxylic acids, which are soluble in bases. ) etergents are made from natural oils and fats, which are not basic. 60. dichloromethane solution containing 5% bromine by volume can be prepared by combining which one of the following? ) 95 ml of dichloromethane and 5 ml of bromine ) 95 g of water and 5 g of bromine that is dissolved in dichloromethane ) 95 ml of water and 5 ml of bromine dissolved in dichloromethane ) 95 g of dichloromethane and 5 g of bromine ) 95 ml of bromine and 5 ml of dichloromethane

32 Lipids Which one of the following shows the product(s) of the reaction of the glyceride (shown at right) with excess bromine? (o stereochemistry is implied by the structures) 2 ( 2 ) 7 ( 2 ) 7 ( 2 ) 8 3 ( 2 ) ( 2 ) 7 ( 2 ) r ( 2 ) 7 r ( 2 ) r ( 2 ) 7 r r ( 2 ) 8 3 r ( 2 ) 7 ( 2 ) 8 3 ( 2 ) 7 ( 2 ) ( 2 ) 7 r ( 2 ) ( 2 ) 7 r ( 2 ) 8 3 r 2 r ( 2 ) 7 + r r ( 2 ) 8 3 r 2 ( 2 ) 7 + ( 2 ) ( 2 ) 7 ( 2 ) ( 2 ) 7 ( 2 ) ( 2 ) 7 r ( 2 ) 8 3 r 2 + ( 2 ) 7 ( 2 ) r r ( 2 ) 7 + r r ( 2 ) 8 3 r r + ( 2 ) 7 ( 2 ) r + ( 2 ) 7 r ( 2 ) 8 3 r

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