Biochemistry : Identifying Specific Nucleic Acid Structures

Study concepts, example questions & explanations for Biochemistry

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Example Questions

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Example Question #1 : Identifying Specific Nucleic Acid Structures

Identify the nucleobase. 

Guanine

Possible Answers:

Thymine

Cytosine

Adenine

Guanine

Uracil

Correct answer:

Guanine

Explanation:

The structure represents guanine because of the characteristic carbonyl group at carbon 6 and amine group and carbon 2.

Example Question #2 : Identifying Specific Nucleic Acid Structures

Identify the nucleobase. 

Adenine

Possible Answers:

Cytosine

Uracil

Guanine

Adenine

Thymine

Correct answer:

Adenine

Explanation:

The structure is adenine because of the characteristic amine group on carbon 6 and lack of any other substituents.

Example Question #3 : Identifying Specific Nucleic Acid Structures

Identify the nucleobase.

Thymine

Possible Answers:

Guanine

Uracil

Cytosine

Adenine

Thymine

Correct answer:

Thymine

Explanation:

The structure represent thymine because of the characteristic carbonyl groups at both carbons 2 and 4 and the methyl group at carbon 5.

Example Question #71 : Identification By Structure

Identify the nucleobase.

Uracil

Possible Answers:

Guanine

Adenine

Uracil

Cytosine

Thymine

Correct answer:

Uracil

Explanation:

The structure represents uracil because of the carbonyl groups attached to both carbons 2 and 4 and the lack of any other substituents.

Example Question #72 : Identification By Structure

Identify the nucleobase. 

Cytosine

Possible Answers:

Uracil

Cytosine

Thymine

Adenine

Guanine

Correct answer:

Cytosine

Explanation:

The structure represents cytosine because of the characteristic amine group on carbon 4, instead of the carbonyl group that is present on carbon 4 of both thymine and uracil.

Example Question #3 : Identifying Specific Nucleic Acid Structures

Which of the following are considered pyrimidines?

I: adenine

II: thymine

III: cytosine

IV: guanine

Possible Answers:

I and IV

II and III

I and III

I and II

III and IV

Correct answer:

II and III

Explanation:

Pyrimidines are nitrogenous bases with 1 ring structure, whereas purines are nitrogenous bases with 2 ring structures. Cytosine and thymine are pyrimidines since they both have one ring structure, whereas adenine and guanine are purines with two connected ring structures. (Note: in RNA, uracil would be considered a pyrimidine in the place of thymine.) One way to help you remember which bases belong to which chemical groups, remember that pyrimidines, like pyramids are sharp, and sharp things CUT - Cytosine, Uracil, and Thymine.

Example Question #7 : Identifying Specific Nucleic Acid Structures

Pyrimidine and purine

Name the given ring systems and determine whether they are soluble or insoluble.

Possible Answers:

Pyrimidine ring; purine ring; soluble

Cytosine; adenine,; soluble

Purine ring; pyrimidine ring; insoluble

Pyrimidine ring; purine ring; insoluble

Amine ring; insoluble

Correct answer:

Pyrimidine ring; purine ring; insoluble

Explanation:

The six-membered ring is a pyrimidine. The purine ring system has two rings: a six-membered and a five-membered ring. These aromatic rings are hydrophobic, making them relatively insoluble. The pyrimidine bases in nucleotides are cytosine, uracil, and thymine; the purine bases in nucleotides are adenine and guanine.

Example Question #8 : Identifying Specific Nucleic Acid Structures

Cytosine

What is the name of the molecule shown?

Possible Answers:

Cytidine

Cytosine

Uracil

Thymine

Pyrimidine

Correct answer:

Cytosine

Explanation:

A nucleoside is the nitrogenous base bound to a sugar via glycosidic bond. A nucleotide is a nitrogenous base bonded to a sugar bonded to the phosphate. This nitrogenous base is cytosine. If it were bound to ribose, it would be called cytidine. Although cytosine is a pyrimidine like uracil and thymine, pyrimidine is a class of ring structure, not the specific name of a base. 

Example Question #71 : Identification By Structure

Adenosine

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Adenine

Purine

Adenosine

Guanosine

Guanine

Correct answer:

Adenosine

Explanation:

While adenine is the name of this nitrogenous base of the purine family, when bonded to ribose, a nucleoside is formed. This nucleoside is called adenosine. A nucleoside consists of a nitrogenous base and a pentose sugar (either ribose or deoxyribose). A nucleotide consists of a nitrogenous base, a pentose sugar, and at least one phosphate group.

Example Question #10 : Identifying Specific Nucleic Acid Structures

Guanosine monophosphate

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Guanosine monophosphate

Guanine phosphate

Guanosine phosphate

Guanine monophosphate

Guanosine-5-monophosphate

Correct answer:

Guanosine-5-monophosphate

Explanation:

When the guanine base is bound to a sugar, it becomes a nucleoside and takes the name guanosine. The 5' indicates that the phosphate is bound to the fifth carbon from the glycosidic bond, linking the base and sugar. Monophosphate indicates that only one phosphate group is bound. Up to three phosphate groups are be bound biologically.

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