GRE Subject Test: Biology : Macromolecules

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

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Example Questions

Example Question #31 : Macromolecules

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

Possible Answers:

The orientation of the hydroxyl group on the anomeric carbon

The direction all hydroxyl groups point in the ring

The number of carbons in the ring

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 #32 : Cell Biology

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

Possible Answers:

Peptide

Phosphodiester

Hydrogen bond

Ionic

Glycosidic

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 #3 : Understanding Carbohydrates

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

Possible Answers:

alpha . . . alpha

alpha . . . beta

beta . . . alpha

beta . . . gamma

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.

Example Question #46 : Dna, Rna, And Proteins

Pick the reason that is least likely to explain why two purines will never be seen attached to each other in a DNA helix.

Possible Answers:

The bulky two-ring structure of purines would cause too much hindrance in the inside of the helix.

Two purines could cause a bump in the DNA, causing problems with transcription and replication.

Purine bases will never be found on opposite DNA strands, so they do not have the ability to pair with one another.

The functional groups at the end of one purine would not correctly match with the other purine. 

Correct answer:

Purine bases will never be found on opposite DNA strands, so they do not have the ability to pair with one another.

Explanation:

DNA strands are composed of millions of nucleotides. As a result, it would be virtually impossible to find a single strand that did not have all four nucleotides.

Nucleotides combine in purine-pyrimidine pairs due to the sterically appropriate fit of the bases, as well as the preferred combination of hydrogen bonds between the two nucleotides. As a result, two purines would not be seen combined. This is due to both being too large when together, and the incorrect hydrigen bonding between their functional groups.

Example Question #33 : Cell Biology

Which of the following is not true of nucleic acids?

Possible Answers:

Both DNA and RNA have nucleotides held together by phosphodiester bonds

Only RNA has a hydroxide group attached to the 2' carbon

ATP and GTP are nucleic acid derivatives

Only DNA is read in the 5'-to-3' direction

Correct answer:

Only DNA is read in the 5'-to-3' direction

Explanation:

DNA and RNA share very similar structures, with two primary differences: DNA lacks a hydroxide group on the 2' carbon of the ribose sugar and RNA uses uracil in place of thymine.

Both DNA and RNA have phosphate groups attached to the 5' carbon of the sugar, which can be joined to the 3' carbon of an adjacent nucleotide by a phosphodiester bond. As a result, both RNA and DNA are read in the 5'-to-3' direction.

Adenosine triphosphate (ATP) and guanosine triphosphate (GTP) are derived from adenine and guanine, two of the fundamental nitrogenous bases in nucleic acids, making them nucleic acid derivatives.

Example Question #32 : Macromolecules

What is the main difference between DNA nucleotides and RNA nucleotides?

Possible Answers:

DNA nucleotides are bound by phosphodiester bonds, but RNA nucleotides are bound by glycosidic bonds

DNA has uracil, while RNA has thymine 

RNA nucleotide bases pair via hydrogen bonds, but DNA nucleotide bases do not 

RNA nucleotides have five-carbon sugars, while DNA nucleotides have six-carbon sugars

RNA nucleotides have two hydroxide groups on the sugar, but DNA nucleotides have only one

Correct answer:

RNA nucleotides have two hydroxide groups on the sugar, but DNA nucleotides have only one

Explanation:

The correct answer is that RNA nucleotides have two hydroxide groups on the sugar, whereas DNA nucleotides have only one hydroxide group. RNA uses uracil in place of thymine; not DNA. Both DNA and RNA have five-carbon sugars and are bound together along the backbone by phosphodiester bonds. Though base pairing is more common in DNA (double-stranded RNA is less common), both utilize hydrogen bonding.

Example Question #35 : Cell Biology

Which of the following are components of a nucleotide?

I. Nitrogenous base

II. Glucose sugar

III. Ribose sugar

IV. Three sulfates

V. Three phosphates

Possible Answers:

I, III, and V

I, II, and IV

I, II, and V

I, II, III, IV, and V

I, III, and IV

Correct answer:

I, III, and V

Explanation:

A nucleotide consists of a nitrogenous base (adenine, guanine, cytosine, thymine, or uracil), a pentose sugar (either ribose or deoxyribose), and three phosphates. These nucleotide monomers can be strung together via phosphodiester linkages to form a polynucleotide. This polynucleotide can base pair with another polynucleotide through hydrogen bonding to form double-stranded DNA.

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