Biochemistry : Identifying Biochemical Molecules

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #2 : Identifying Specific Nucleic Acid Structures

Cytosine

What is the name of the molecule shown?

Possible Answers:

Thymine

Cytidine

Pyrimidine

Cytosine

Uracil

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 #6 : Identifying Specific Nucleic Acid Structures

Adenosine

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Purine

Adenosine

Adenine

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 #1 : Identifying Specific Nucleic Acid Structures

Guanosine monophosphate

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Guanine phosphate

Guanine monophosphate

Guanosine-5-monophosphate

Guanosine phosphate

Guanosine 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.

Example Question #71 : Identification By Structure

Uracil

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Thymidine

Uridine

Uracil

Thymine

Uracine

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 #12 : Identifying Specific Nucleic Acid Structures

Adenine

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Adenine

Guanosine

Adenosine

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 #11 : Identifying Specific Nucleic Acid Structures

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 #82 : Identification By Structure

Uracil

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Thymidine

Thymine

Uracil

Cytosine

Pyrimidine

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 #83 : Identification By Structure

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

Possible Answers:

Uracil

Adenine

Uracil

Adenine

Cytosine

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 #12 : Identifying Specific Nucleic Acid Structures

3  5  phosphodiester bond

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

Possible Answers:

3',5' phosphate bond

3',5' phosphoester bond

5',3' phosphoester bond

5',3' phosphodiester bond

3',5' 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 #11 : Identifying Specific Nucleic Acid Structures

Atp

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Adenine-5-triphosphate

Adenosine-5-phosphate

Adenine triphosphate

Adenosine-5-triphosphate

Adenosine 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.

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