Biochemistry : Identifying Specific Nucleic Acid Structures

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #341 : Biochemistry

Uracil

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Uracine

Thymine

Uracil

Thymidine

Uridine

Correct answer:

Uracil

Explanation:

This is an image of the nitrogenous base uracil. Although very similar to the structure of thymine, they differ by a methyl group at the fifth carbon. (Start counting at the nitrogen at the bottom of the structure and count clockwise). If the uracil were bound to a sugar, it would be uridine.

Example Question #342 : Biochemistry

Adenine

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Adenine

Adenosine

Guanosine

Purine

Guanine

Correct answer:

Adenine

Explanation:

This nitrogenous base is adenine. Although it has a purine ring system, purine is not its specific name. If the adenine were bound to a sugar, it would be called adenosine.

Example Question #81 : Identification By Structure

Guanine

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Guanine

Guanosine

Adenine

Purine

Adenosine

Correct answer:

Guanine

Explanation:

This nitrogenous base is guanine. Although it has a purine ring system, purine is not its specific name. If the guanine were bound to a sugar, it would be called guanosine.

Example Question #343 : Biochemistry

Uracil

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Pyrimidine

Thymidine

Cytosine

Uracil

Thymine

Correct answer:

Thymine

Explanation:

This nitrogenous base is thymine. Although it has a pyrimidine ring system, pyrimidine is not its specific name. If the thymine were bound to a sugar, it would be called thymidine.

Example Question #11 : Identifying Specific Nucleic Acid Structures

Which of the following nitrogenous bases is found exclusively in DNA?

Possible Answers:

Cytosine

Adenine

Adenine

Uracil

Uracil

Correct answer:

Uracil

Explanation:

Thymine is the nitrogenous base that is only found in DNA. All of the other bases can be found in both DNA and RNA.

Example Question #84 : Identification By Structure

3  5  phosphodiester bond

Describe the bond indicated by the box in the given figure.

Possible Answers:

3',5' phosphodiester bond

5',3' phosphoester bond

3',5' phosphoester bond

3',5' phosphate bond

5',3' phosphodiester bond

Correct answer:

3',5' phosphodiester bond

Explanation:

The 3',5' phosphodiester bond describes the way the bond occurs. The oxygen in the 3' hydroxyl group in the nucleotide on the top bonds to the phosphorus of the 5' phosphate group of the nucleotide on the bottom. The bond consists of a

carbon-oxygen-phosphorus-oxygen-carbon direct linkage. Carbon-oxygen-phosphorous and posphorous-oxygen-carbon are two separate esters, hence the "diester" part of the name. 

Example Question #82 : Identification By Structure

Atp

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Adenosine triphosphate

Adenosine-5-phosphate

Adenine-5-triphosphate

Adenine triphosphate

Adenosine-5-triphosphate

Correct answer:

Adenosine-5-triphosphate

Explanation:

This nucleotide is adenosine-5-triphosphate, also known as ATP. When the nitrogenous base adenine is bound to a sugar, it becomes a nucleoside called adenosine. The carbon in the ribose at the site of the glycosidic bond is referred to as the 1' carbon. If we count clockwise, we will see that the phosphates are bound at the 5' carbon. Because there are three phosphate groups bound, the nomenclature must be 5-triphosphate.

Example Question #82 : Identification By Structure

Cytidine

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Adenosine

Uridine

Deoxycytidine

Cytidine

Cytosine

Correct answer:

Cytidine

Explanation:

This nucleoside is cytidine. If the base were not bound to the sugar, this would be cytosine. If the 2' hydroxyl group were missing, this structure would be deoxycytidine. (The 2' hydroxyl is the  closest to the glycosidic bond between the base and the sugar). 

Example Question #83 : Identification By Structure

Which of the following composes nucleotides?

Possible Answers:

Pentose, nitrogenous base, phosphate

Ribose, nitrogenous base, phosphate

Purines, pyrimidines, pentose, nucleotide base

Phosphate, nitrogenous base, fructose

Nitrogenous base, phosphate, glucose

Correct answer:

Pentose, nitrogenous base, phosphate

Explanation:

Nucleotides are formed by a pentose sugar (either ribose or deoxyribose), a nitrogenous base (adenine, cytosine, guanine, thymine, or uracil), and one or more phosphate groups. Polymers of nucleotides are known as nucleic acids (DNA and RNA).

Example Question #82 : Identification By Structure

Which of the following nucleic acid bases is not in the right category?

Possible Answers:

Adenine - purine

Cytosine - pyrimidine

Guanine - purine

Thymine - pyrimidine

Uracil - purine

Correct answer:

Uracil - purine

Explanation:

The pyrimidines, which contain a single six-membered ring, are uracil, cytosine, and thymine. The purines, which contain a six-membered ring and a five-membered ring, are adenine and guanine. A mnemonic to help you remember these two groups is that pyrimidines, like pyramids are sharp - and sharp things CUT (cytosine, uracil, thymine).

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