Biochemistry : Lipids

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #541 : Biochemistry

Which of these are not found in cell membranes?

Possible Answers:

Cholesterol

Phosphoacylglycerols

Triacylglycerols

Glycolipids

Correct answer:

Triacylglycerols

Explanation:

Phosphoacylglycerols, glycolipids, and cholesterol are all part of cell membranes. Phosphoacylglycerols and glycolipids are major components of cell membranes. Glycolipids mainly have a communicative role in which they act as markers for cell recognition. They also provide stability for the cell and help form tissues. Cholesterol helps maintain the fluidity of cell membranes, along with securing important proteins in the membrane.

Triacylglycerols, however, are not found in cell membranes. These are triesters formed by esterification of three fatty acids to glycerol. Oils are triacylglycerols that are liquids at room temperature, while fats are triacylglycerols that are solids at room temperature. Triacylglycerols are stored forms of energy for living systems.

Example Question #121 : Macromolecule Fundamentals

Which of these fatty acids is expected to have the highest melting point?

Possible Answers:

18:0

12:0

20:0

14:3

16:3

Correct answer:

20:0

Explanation:

The less double bonds there are (sites of unsaturation) and the more carbons there are in a fatty acid, the higher the melting point for a fatty acid. This is due to the difference in the three-dimensional chemical shape of such fatty acids - saturated fatty acids have linear hydrocarbon chains, which allows them to stack closely together and maximize intermolecular forces within the chains whereas unsaturated fatty acids contain a "kink" in their hydrocarbon chains, which does not allow two unsaturated fatty acids to associate very closely to one another, thereby not maximizing intermolecular forces of attraction between them. This means that the saturated fatty acids require more energy to overcome the higher quantity of intermolecular forces in order for a phase change to occur than do unsaturated fatty acids. Based on this reasoning, the 20:0 fatty acid (which has 20 carbons and zero double bonds) is expected to have the highest melting point. 

Example Question #551 : Biochemistry

Which of the following can be used to describe fatty acids?

Possible Answers:

Hydrophobic

Hydrophilic

Amphoteric

Inorganic

Amphipathic 

Correct answer:

Amphipathic 

Explanation:

Fatty acids are composed of a carboxylic acid head and a long carbon chain. The carbon chain is non-polar, while the carboxylic acid head is polar. A molecule with both a polar and non-polar parts is known as amphipathic. The word amphoteric means a molecule that can act as either an acid or a base. Finally, just as a fatty acid has both polar and non-polar ends, those same ends are also hydrophilic and hydrophobic, respectively.  

Example Question #131 : Macromolecule Fundamentals

What is an amphipathic molecule?

Possible Answers:

Molecules in crystalline form

A molecule that has both polar and nonpolar region

Basic ions

A class of wax molecules

Acidic ions

Correct answer:

A molecule that has both polar and nonpolar region

Explanation:

An amphipathic molecule has both polar and nonpolar domains. Long-chain fatty acids are examples of amphipathic molecules.

Example Question #22 : Lipids

Poison ivy, poison oak, and poison sumac produce a compound called urushiol. Urushiol is a mixture of compounds containing catechols with long-chain alkyl groups. The severity of the allergic reaction depends on the degree of unsaturation of the alkyl groups.

If you are exposed to poison ivy, which treatment would be most effective?

Possible Answers:

Wash the area with soap and water

Wash the area with saline

Wash the area with cold water

Wash the area with dilute vinegar or lemon juice

Wash the area with soap, water, and baking soda (sodium bicarbonate)

Correct answer:

Wash the area with soap, water, and baking soda (sodium bicarbonate)

Explanation:

Soap and water will work, as urushiol is amphipathic, but the addition of sodium bicarbonate is more effective. Sodium bicarbonate is a weak base and will make the urushiol more polar - and therefore more water-soluble. 

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