Biochemistry : Fatty Acids

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #1 : Lipid Structures And Functions

Which of the following statements about oleic acid is false?

Possible Answers:

Its condensed molecular formula is 

None of the other answers is false

There are 16 carbon atoms in its longest chain

Its IUPAC name is (9Z)-Octadec-9-enoic acid

It is a fatty acid with an omega-9 unsaturation

Correct answer:

There are 16 carbon atoms in its longest chain

Explanation:

Oleic acid (which composes much of olive oil) has a double bond between its 9th and 10th atoms. Hence it has an omega-9 unsaturation. It has 18 carbon atoms, not 16, which gives it a condensed molecular formula:. Because it is a cis-isomer, the IUPAC name contains a Z, and becuse it is an unsaturated carboxylic acid, it ends in -enoic acid.

Example Question #2 : Lipid Structures And Functions

Which of the following factors contribute to increasing the melting point of a fatty acid?

Possible Answers:

Decrease fatty acid chain length

Introducing cis-double bonds

Increased number of double bonds

Increased fatty acid chain length

Adding methylene groups

Correct answer:

Increased fatty acid chain length

Explanation:

Double bonds cause unsaturation, thus decreases the melting point. Cis-double bonds as well as methylation also introduce kinks within the chain, decreasing the melting point. Increasing the fatty acid chain length creates saturation, thus causes the melting point to increase. Therefore, decreasing fatty acid chain length has the adverse effect.

Example Question #2 : Lipid Structures And Functions

How many hydrogens are bound to a carbon atom in the middle of a saturated fatty acid chain?

Possible Answers:

Correct answer:

Explanation:

In a saturated fatty acid, all of the covalent carbon to carbon bonds are single bonds. So a carbon atom in the middle of the chain will have two covalent bonds to other carbon atoms, and can therefore bond to two hydrogen atoms. 

Example Question #3 : Lipid Structures And Functions

Select the most accurate description of alpha-linolenic acid.

Possible Answers:

Can be synthesized de novo in the body

Is a precursor for arachidonic acid (AA)

Is a twenty-carbon chain omega-3 fatty acid

Is a precursor for eicosapentaenoic acid (EPA)

Is an eighteen-carbon chain omega-6 fatty acid

Correct answer:

Is a precursor for eicosapentaenoic acid (EPA)

Explanation:

Alpha-linolenic acid is an essential fatty acid that must be consumed in the diet (cannot be synthesized by the body). It is an eighteen-carbon omega-3 fatty acid that is used to synthesize eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), two important long chain polyunsaturated fatty acids. Alpha-linoleic acid is the precursor to arachodonic acid (AA).

Example Question #2 : Lipid Structures And Functions

Which of the following is not an omega-3 fatty acid?

Possible Answers:

Eicosapentaenoic acid (EPA)

Docosahexaenoic acid (DHA)

Alpha-linolenic acid (ALA)

docosapentaenoic acid (DPA)

Dihomo-gamma-linolenic acid (DGLA)

Correct answer:

Dihomo-gamma-linolenic acid (DGLA)

Explanation:

Dihomo-gamma-linolenic acid (DGLA) is a twenty-carbon omega-6 fatty acid that is a desaturation product of linoleic acid. The rest of the answer choices are indeed omega-3 fatty acids.

Example Question #5 : Lipid Structures And Functions

Omega-6 fatty acids are primarily found in __________.

Possible Answers:

chia seeds

poultry

flax seeds

salmon

krill

Correct answer:

poultry

Explanation:

Omega-6 fatty acids are primarily found in vegetable oils (ex. soybean oil or corn oil), chicken, and eggs. Note that poultry feed is very heavy on corn products and thus increases the omega-6 fatty acid proportion of almost all farm raised animals. Fish, chia seeds, and flax seeds are high in omega-3 fatty acids.

Example Question #1 : Fatty Acids

Omega-3 fatty acids __________.

Possible Answers:

can be used to synthesize anti-inflammatory (or less-inflammatory) eicosanoids

are a substrate for the synthesis of series 2 prostaglandins

have a double bond at the 6th carbon

are found in most vegetable oils

are considered pro-inflammatory

Correct answer:

can be used to synthesize anti-inflammatory (or less-inflammatory) eicosanoids

Explanation:

Omega-3 fatty acids can be utilized as a substrate for the synthesis of series 3 prostaglandins (a subclass of eicosanoids), and are generally considered "anti-inflammatory" for this reason. Furthermore, omega-3 fatty acids are so named for having a double bond at the 3rd carbon from the omega end. They are generally found in fish and flax and chia seeds, while omega-6 fatty acids are in poultry and vegetable oils.

Example Question #7 : Lipid Structures And Functions

If arachidonic acid is used as a substrate for eicosanoid synthesis, what type of eicosanoid can be produced?

Possible Answers:

Prostaglandin I3 (PGI3)

Thromboxane A2 (TXA2)

Thromboxane A1 (TXA1)

Thromboxane A3 (TXA3)

Correct answer:

Thromboxane A2 (TXA2)

Explanation:

Arachidonic acid (AA) is used as a substrate for series 2 eicosanoid synthesis, including thromboxane A2 (TXA2). Series 3 eicosanoids are synthesized from alpha-linolenic acid (ALA), and series 1 are synthesized from dihomo-gamma-linolenic acid (DGLA).

Example Question #2 : Fatty Acids

Which of the following is true of eicosanoids produced from alpha-linolenic acid?

Possible Answers:

They produce a weak platelet aggregation response

Their production is increased by adding vegetable oil in the diet

They produce a strong platelet aggregation response

They are considered pro-inflammatory

A decreased amount is recommended for those with high risk of heart disease

Correct answer:

They produce a weak platelet aggregation response

Explanation:

Alpha-linolenic acid (ALA) is an omega-3 fatty acid that is utilized to produce series 3 eicosanoids. Series 3 eicosanoids lead to a weak platelet aggregation response, and are considered anti or less-inflammatory. Thus, a diet rich in omega-3 fatty acids is recommended for those with heart disease risk. Omega-3 fatty acids are primarily found in fish or flax and chia seeds, not vegetable oil, which is rich in omega-6 fatty acids.

Example Question #5 : Lipid Structures And Functions

Micelle formation is a result of which of these?

Possible Answers:

Hydrogen bonding between water and the polar head of free fatty acids

Hydrophobic interactions with the polar head of free fatty acids

Covalent bonding between fatty acids and water

Hydrogen bonding between water and the carbon chain end of free fatty acids

Hydrophobic interactions with the carbon chain end of free fatty acids

Correct answer:

Hydrophobic interactions with the carbon chain end of free fatty acids

Explanation:

The hydrocarbon tail of free fatty acids is nonpolar, and so it interacts unfavorably with water molecules.  So, when free fatty acids are placed in a polar environment, the nonpolar tails are driven together and inward in order to avoid water molecules.  A micelle is formed from the circular formation of free fatty acids. 

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