GRE Subject Test: Biology : Other Macromolecules

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

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Example Questions

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Example Question #23 : Gre Subject Test: Biology

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

Possible Answers:

Steroid

Sucrose

ATP

Glycine

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 #1 : Lipids

Which of the following molecules is amphipathic?

Possible Answers:

Triglyceride

Maltose

Phospholipid

Glutamate

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 #1 : Understanding Lipids

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

Possible Answers:

Sterols

Glycerolipids

Glycolipids

Glycerophospholipids

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 #25 : Gre Subject Test: Biology

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

Possible Answers:

An eighteen-carbon fatty acid chain

A twelve-carbon fatty acid chain

A fourteen-carbon fatty acid chain

A twenty-four-carbon fatty acid chain

A nineteen-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 #26 : Gre Subject Test: Biology

A phospholipid contains which of the following components?

I. Fatty acids

II. Phosphate

III. Sulfate

IV. Glycerol

Possible Answers:

I, II, and IV

I, III, and IV

I and IV

II and IV

I and II

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 

Example Question #24 : Cell Biology

What factor determines whether humans are capable of digesting a polysaccharide?

Possible Answers:

The linkage between monomers

The number of monomers in the polysaccharide

The number of carbons in the carbohydrate

The branching pattern of the polysaccharide

Correct answer:

The linkage between monomers

Explanation:

Carbohydrate monomers (monosaccharides) can be joined together with either alpha or beta linkages. Humans have the enzymes necessary in order to break down alpha linkages, but not beta linkages. Cellulose is a polysaccharide in which the monomers joined together by beta linkages, so humans cannot digest cellulose. Some bacterial species are capable of cleaving these linkages and have developed symbiotic or mutualistic relationships with animals. These bacterial species inhabit the mammalian digestive tract, cleaving beta linkages and gaining protection from the outside environment.

The size and branching pattern of a carbohydrate do not affect its ability to be digested.

Example Question #1 : Understanding Carbohydrates

Which polysaccharide is the primary form of energy storage in plants?

Possible Answers:

Starch

Glycogen

Peptidoglycan

Cellulose

Correct answer:

Starch

Explanation:

The two most common polysaccharides found in plant cells are starch and cellulose. Starch is the primary source of energy storage, while cellulose is used to construct the plant's cell walls.

Example Question #2 : Understanding Carbohydrates

What is the difference between the alpha and beta forms of a monosaccharide?

Possible Answers:

The direction all hydroxyl groups point in the ring

The number of carbons in the ring

The orientation of the hydroxyl group on the anomeric carbon

Whether the monosaccharide is an aldose or a ketose

Correct answer:

The orientation of the hydroxyl group on the anomeric carbon

Explanation:

When a monosaccharide becomes cyclic in form, the anomeric carbon can have its hydroxyl group pointing in the same direction as the methoxy group, or oriented in the opposite direction. This orientation determines whether the sugar is considered alpha or beta.

Example Question #2 : Other Macromolecules

Two monosaccharides can be linked together to form a disaccharide. This linkage is known as a __________ bond.

Possible Answers:

Hydrogen bond

Phosphodiester

Peptide

Glycosidic

Ionic

Correct answer:

Glycosidic

Explanation:

Carbohydrates are linked together to form disaccharides and other polysaccharides through glycosidic linkages. A glycosidic linkage is one in where two sugar molecules are bridged by an oxygen atom. Peptide linkages are found between amino acids and phosphodiester bonds are found between nucleic acid monomers. Ionic bonds involve the complete transfer of one or more electrons from one species to another. Hydrogen bonds are weak intermolecular and intramolecular forces that contribute to the stability of many substances such as liquid water.

Example Question #31 : Cell Biology

Glycogen and starch are polysaccharides connected through __________ linkages, and cellulose is connected via __________ linkages.

Possible Answers:

alpha . . . alpha

alpha . . . beta

beta . . . gamma

beta . . . alpha

alpha . . . gamma

Correct answer:

alpha . . . beta

Explanation:

Glycogen and starch molecules are connected by alpha linkages. Glycogen and starch can be digested by humans because we have an enzyme capable of separating these linkages to produce monosaccharides. Cellulose on the other hand is connected through beta linkages. These beta linkages allow for the polysaccharide to form straight chains which can serve structural purposes such as plant cell walls. Cellulose, however, cannot be digested by humans because we do not have enzymes capable of severing these linkages.

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