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Example Questions
Example Question #1 : Biological Molecules
Which of the following lipids is polyunsaturated?
I. (9Z,12Z,15Z)-octadeca-9,12,15-trienoic acid
II. Octadecanoic acid
III. (9Z,12Z)-octadeca-9,12-dienoic acid
IV. (9Z)-9-Octadecenoic acid
II and III
I and IV
I, III, and IV
II only
I and III
I and III
This question tests your knowledge of what an unsaturated lipid is, as well as your ability to obtain structural information from IUPAC names.
Firstly, a polyunsaturated lipid is a long carboxylic acid hydrocarbon chain that features multiple unsaturations, or double bonds. Remember from nomenclature that the stem "-en" indicates double bonds, or alkenes, while "-an" indicates alkanes, or fully saturated hydrocarbons. The relevant stems in the answer choices are italicized below:
I. (9Z,12Z,15Z)-octadeca-9,12,15-trienoic acid
II. Octadecanoic acid
III. (9Z,12Z)-octadeca-9,12-dienoic acid
IV. (9Z)-9-Octadecenoic acid
As you can see, "trien" and "dien" in I and III indicate these lipids are polyunsaturated, while "an" in II indicates a fully saturated lipid and "en" in IV indicates a monounsaturation. The lipids are drawn below as well, with the alkenes in polyunsaturated lipids circled in red, and the alkene in the monounsaturated lipid circled in green.
Example Question #1 : Help With Organic Lipids
What is the name of the pictured fatty acid?
Arachidonic acid
Palmitoleic acid
Eicosapentaenoic acid
Linoleic acid
Oleic acid
Arachidonic acid
The pictured structure represents arachidonic acid due to the 20-carbon carboxylic acid chain with characteristic unsaturated (double) bonds after carbons 5, 8, 11, and 14.
Example Question #171 : Organic Concepts
Other than the traditional numerical system, the X marking the terminal carbon in the structure shown here can be labeled how?
Alpha-1
Omega-18
Gamma-18
Alpha-18
Omega-1
Omega-1
Fatty acids can be labeled numerically from 1-X, or they can be labeled in reverse starting with omega-1 as the terminal carbon.
Example Question #261 : Biochemistry
Identify the common name of the fatty acid shown here.
Arachidonic acid
Palmitic ccid
Linoleic acid
Oleic acid
Myristic acid
Oleic acid
Oleic acid is a fatty acid consisting of 18 carbon molecules and a single unsaturated (double) bond after carbon 9, as pictured.
Example Question #2 : Help With Organic Lipids
What type of lipid is shown below?
Phosphatidylcholine
Steroid
Phospholipid
Triglyceride
Fatty acid
Triglyceride
A triglyceride consists of three fatty acid chains bound to a glycerol backbone via ester bonds, as shown by the pictured structure.
Example Question #1 : Help With Organic Lipids
Three fatty acid chains can be bound to a glycerol backbone via ester bonds to form a triglyceride. What type of chemical reaction is this?
Oxidation-reduction
Hydrolysis
Markovnikov
Condensation
Hoffman elimination
Condensation
The reaction described is an esterification in which water is a product—as is characteristic of a condensation reaction—and in which an ester bond is formed to connect the fatty acid chain and the glycerol molecule.
Example Question #1 : Help With Organic Lipids
An unknown molecule was found to have a molecular formula of . This molecule can be identified as a __________.
None of these
triaclyglycerol
fatty acid
steroid
None of these
This question is a little bit tricky. At first glance, we would jump to the conclusion that this molecule is a long hydrocarbon chain attached to a carboxylic acid and, therefore, a fatty acid. The premise is correct. However, our conclusion is false because, by convention, a fatty acid must contain a carbon chain of at least 12 carbons. The given formula does not match the description for a steroid or triacylglycerol. The correct answer is none of these.
Example Question #3 : Help With Organic Lipids
What is the primary biological function of a fatty acid?
All of these
To serve as a medium for energy storage
To serve as a medium for the derivation of other important lipids
To serve as a water barrier on the outside of leaves and feathers
To serve as a medium for the derivation of other important lipids
The primary biological function of a fatty acid is to serve as a medium for the derivation of other important lipids such as waxes, triacylglycerols, phospholipids, and other necessary lipids.
Example Question #251 : Organic Chemistry
Before the advent of synthetic soap, hand soap was made from animal fat, namely triacylglycerols. What property of triacylglycerols make them an ideal component in hand soap?
The ability to engulf dirt/grease on skin
None of these
The ability to engulf and digest harmful bacteria on skin
The presence of hydrophobic tails and hydrophilic heads that work to dissolve into and remove dirt/grease on the skin
The presence of hydrophobic tails and hydrophilic heads that work to dissolve into and remove dirt/grease on the skin
A triacylglycerol is derived from the hydrolysis of glycerols and fatty acids. Triacylglycerols have hydrophobic hydrocarbon tails and hydrophilic heads (amphipathic). The hydrophobic tails dissolve into dirt/grease on the skin while the hydrophilic tails work with running water to suspend and remove the dissolved impurities.
Example Question #1 : Help With Organic Lipids
Based on the formula and structure of this molecule, this molecule can be classified as a __________.
wax
protein
fatty acid
complex sugar
wax
The correct answer is the lipid, wax. Lipids can often be identified based on their structure alone. The general structure of wax is an ester with two long carbon chains on each end of the ester, as seen in this problem. Additionally, fatty acids can be identified simply as long carbon chains with a carboxylic acid on one end, while the general structure of steroids can be seen as four connected hydrocarbon rings.
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