FST 100A HW5: Lipid Reactions - Exam #2

Which of the following correctly describes acyl chain "w" below? (Choose all correct answers) 1)It is an ω-3 fatty acid chain 2)It is diunsaturated 3)It is unsaturated 4)It is an 18:2Δ9,12 chain 5)It is a long chain fatty acid

2)It is diunsaturated 3)It is unsaturated 4)It is an 18:2Δ9,12 chain 5)It is a long chain fatty acid

Which of the following contains 3 acyl groups? 1)A diacylglycerol molecule 2)A free fatty acid molecule 3)A phospholipid molecule 4)A wax molecule 5)A triacylglycerol molecule

A triacylglycerol molecule

Water acts as a nucleophile in which of the following reactions? 1)Lipid oxidation 2)Enzymatic browning 3)Hydroperoxide decomposition 4)Hydrogenation 5)Acid-catalyzed lipid hydrolysis

Acid-catalyzed lipid hydrolysis

Which of the acyl chains on this structure are saturated? (Choose all correct answers) 1)Chain z 2)Chain w 3)Chain u

Chain u and z

Tropical plant Examples and Key fatty acid groups

Cocoa butter, palm, coconut and 16:0, 18:0, 18:1

Which of these groups would be slowest to oxidize? Fatty acid groups A and B would be equally slow and more stable than the rest to oxidation 1)Fatty acid chain A 2)Fatty acid chain B 3)Fatty acid chain D 4)Fatty acid chain C

Fatty acid chain B

How does storing foods in opaque or colored containers slow down oxidation? 1)Hydroperoxide decomposition requires light energy to occur 2)It decreases the rate of production of singlet oxygen by blocking light energy 3)It deactivates lipoxygenase, which requires light energy to function 4)In the dark, double bonds on fatty acids become conjugated and therefore more stable 5)The opaque containers keep out oxygen better than clear ones do

It decreases the rate of production of singlet oxygen by blocking light energy

Stearic acid (18:0) has a melting temperature of 69˚C. Based on this value, which melting temperature given below is incorrect? 1)Melting temperature for 18:1(cis): 16˚C 2)Melting temperature for 18:2(cis): -5˚C 3)Melting temperature for 18:1(trans): 80˚C 4)Melting temperature for 16:0: 63˚C 5)Melting temperature for 8:0: 16˚C

Melting temperature for 18:1(trans): 80˚C

Which of the above triglyceride structures would have the highest melting point? (St: stearic acid; P: palmitic acid; O: oleic acid; L: linoleic acid) 1)Structure IV 2)Structure II 3)These structures would all have similar melting temperatures 4)Structure III 5)Structure I

Structure I

Which of the following best characterizes the lipids in cold-water fish? 1)They are useful as semi-solid shortenings 2)They strongly raise LDL:HDL ratios 3)They spontaneously hydrogenate when exposed to air 4)They melt at around 37˚C 5)They oxidize more rapidly than most food lipids

They oxidize more rapidly than most food lipids

Cholesterol is (choose all correct answers) 1)a steroid 2)a terpene 3)a lipid 4)water insoluble

a steroid a lipid water insoluble

The sn-2 chain on the above triglyceride corresponds to 1)chain w 2)Either chain w or z (it is impossible to distinguish) 3)There are no stereocarbons on this structure, so the sn numbering 4)does not apply 5)chain u 6)chain z

chain u

Fish oil examples and Key fatty acid groups?

cod, salmon and 16:0, 16:1, 18:1, 22:6.

Temperate plant examples and Key fatty acid groups

corn, peanut, olive, soy, sun-flower and 18:1, 18:2

Milk fat (ruminants) example and Key fatty acid groups?

cow's milk and 4:0, 6:0, 14:0, 16:0, 18:1.

The chemical reaction shown below is an example of 1)oxidation 2)esterification 3)scission 3)lipolysis 4)reduction

esterification

Of the fatty acid chains shown above, linolenic acid is 1)None of the structures shown 2)fatty acid chain A 3)fatty acid chain B 4)fatty acid chain C 5)fatty acid chain D

fatty acid chain C

Hydrogenation (partial or full) of group C (shown above) could produce (choose all correct answers) 1)fatty acid group D 2)fatty acid group A 3)trans double bonds 4)fatty acid group B

fatty acid group D fatty acid group A trans double bonds fatty acid group B

A good antioxidant will (choose all correct answers) 1)give up a hydrogen less readily than would a lipid molecule 2)form free radicals that are not themselves highly reactive 3)form a resonance hybrid free radical with many contributing structures

form free radicals that are not themselves highly reactive form a resonance hybrid free radical with many contributing structures

After interesterification, this mixture of triglyceride structures would most likely (choose all correct answers) smell rancid would have primarily trans double bonds be almost completely unsaturated be almost completely saturated have a different melting range

have a different melting range

A lipid with this distribution of triglycerides would (Choose all correct answers) be described as homogeneous have a wide melting range be completely melted above 20˚C

have a wide melting range

Milk fat (ruminants) Saturated/ Unsaturated and Characteristic TG structure(s)?

high fraction of S and U.

Animal Storage Saturated/ Unsaturated and Characteristic TG structure(s)?

high fraction of S and U. Heterogenous: SUS, SSS, SUU, SSU.

Fish oil Saturated/ Unsaturated and Characteristic TG structure(s)?

high fraction of U.

Temperate plant Saturated/ Unsaturated and Characteristic TG structure(s)?

high fraction of U. UUU structure

Tropical plant Saturated/ Unsaturated? Characteristic TG structure(s)?

high fraction of both S and U. SUS

Cocoa butter 1)consists of a large variety of triglyceride structures 2)forms a crystal only for temperatures below 10˚C 3)melts over a wide range of temperatures 4)has few saturated fatty acid chains 5)is more than 80% unsaturated at the sn-2 position

is more than 80% unsaturated at the sn-2 position

Initiation of lipid oxidation occurs by the action of (choose all correct answers) 1)light captured by sensitizer molecules 2)transition metals 3)enzymes called lipoxygenases 4)reactive oxygen species (ROS•)

light captured by sensitizer molecules transition metals enzymes called lipoxygenases reactive oxygen species (ROS•)

All triglycerides, monoglycerides, waxes and phospholipids are (choose all correct answers) 1)lipids 2)strongly amphiphilic 3)poorly soluble in water

lipids poorly soluble in water

At sufficiently high temperature, triglycerides melt because (choose all correct answers) 1)molecular arrangements in liquids are more disordered than in a crystalline solid 2)intermolecular interactions become stronger at high temperature 3)entropic contributions are more important at high temperature

molecular arrangements in liquids are more disordered than in a crystalline solid entropic contributions are more important at high temperature

Animal storage examples and Key fatty acid groups?

tallow, lard and 16:0, 18:0, 18:1

In this reaction, the C-H bond breaks (shown in red) 1)heterolytically 2)to send both electrons towards the C 3)to send one electron to C, the other to H 4)homolytically

to send one electron to C, the other to H homolytically