GRE Subject Test: Biology : Understanding Lipids

Study concepts, example questions & explanations for GRE Subject Test: Biology

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Example Questions

Example Question #1 : Understanding Lipids

Which of the following requires a carrier protein in order to be transported through the bloodstream?

Possible Answers:

ATP

Sucrose

Glycine

Steroid

Correct answer:

Steroid

Explanation:

Blood is an aqueous solution and will easily dissolve polar, hydrophilic molecules. Nonpolar molecules, however, do not easily exist in this solution and require a bound polar group, such as a carrier protein, to exist in equilibrium.

Proteins, carbohydrates, and nucleic acids all contain polar groups, allowing them to dissolve in the blood. Lipids, however, are nonpolar and require transport proteins. Steroids are a class of lipids and will require protein assistance for transport in the blood.

Sucrose is a carbohydrate, glycine is a polar amino acid, and ATP is a polar nucleic acid derivative.

Example Question #2 : Other Macromolecules

Which of the following molecules is amphipathic?

Possible Answers:

Glutamate

Maltose

Phospholipid

Triglyceride

Correct answer:

Phospholipid

Explanation:

Amphipathic molecules contain both polar and nonpolar regions, making them an extremely diverse class with an array of functions. For example, bile is an amphipathic molecule whose nonpolar region interacts with fats and whose polar region interacts with the aqueous environment of the small intestine.

Most lipids are entirely nonpolar and hydrophobic. Phospholipids, however, are formed from a glycerol molecule bound to two hydrophobic fatty acid tails and a hydrophilic phosphate head. This structure allows phospholipids amphipathic properties. Most notably, phospholipids are able to interact with the aqueous environments in the cell cytosol and extracellular environment, while maintaining the hydrophobic region of the cell membrane that acts as a semipermeable barrier.

Triglycerides are considered nonpolar. Glutamate is an acidic amino acid with highly polar properties. Maltose is a six-carbon sugar (carbohydrate) and is highly polar.

Example Question #3 : Other Macromolecules

Which of the following lipid classifications has the primary purpose of storing energy for the body?

Possible Answers:

Glycolipids

Sterols

Glycerophospholipids

Glycerolipids

Correct answer:

Glycerolipids

Explanation:

Lipids have a variety of functions in the human body, one of which is the storage of energy for later use. This function is accomplished by triglycerides (also called triacylglycerols), which belong to the class of glycerolipids.

Example Question #2 : Understanding Lipids

Fatty acids can vary in length. Which of the following fatty acids chains cannot not be synthesized in the human body?

Possible Answers:

A twenty-four-carbon fatty acid chain

A twelve-carbon fatty acid chain

A fourteen-carbon fatty acid chain

A nineteen-carbon fatty acid chain

An eighteen-carbon fatty acid chain

Correct answer:

A nineteen-carbon fatty acid chain

Explanation:

Fatty acids synthesized in the human body always have an even number of carbon atoms usually between 12 and 28. Odd-numbered fatty acid chains will occasionally be found in plants and marine animals.

Example Question #3 : Understanding Lipids

A phospholipid contains which of the following components?

I. Fatty acids

II. Phosphate

III. Sulfate

IV. Glycerol

Possible Answers:

I, III, and IV

I and IV

II and IV

I and II

I, II, and IV

Correct answer:

I, II, and IV

Explanation:

A phospholipid is made up of two fatty acids and a phosphate group with an R-group attached to a glycerol backbone. The phosphate group allows for one end of the molecule to be polar while the fatty acids allow for the other part to be nonpolar. Phospholipids are a major component of the bilayered cellular membrane 

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