Biochemistry : Identifying Biochemical Molecules

Study concepts, example questions & explanations for Biochemistry

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Example Questions

Example Question #75 : Identification By Structure

Cytosine

What is the name of the molecule shown?

Possible Answers:

Thymine

Uracil

Pyrimidine

Cytidine

Cytosine

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 #76 : Identification By Structure

Adenosine

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Guanine

Guanosine

Purine

Adenine

Adenosine

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 #78 : Identification By Structure

Guanosine monophosphate

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Guanosine monophosphate

Guanine phosphate

Guanosine phosphate

Guanosine-5-monophosphate

Guanine 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 #131 : Identifying Biochemical Molecules

Uracil

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Uracil

Thymine

Thymidine

Uracine

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 #132 : Identifying Biochemical Molecules

Adenine

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Adenosine

Purine

Guanosine

Guanine

Adenine

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

Purine

Adenosine

Adenine

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 #12 : Identifying Specific Nucleic Acid Structures

Uracil

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Uracil

Cytosine

Thymine

Thymidine

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 #133 : Identifying Biochemical Molecules

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

Possible Answers:

Cytosine

Uracil

Uracil

Adenine

Adenine

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 #134 : Identifying Biochemical Molecules

3  5  phosphodiester bond

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

Possible Answers:

3',5' phosphoester bond

5',3' phosphoester bond

3',5' phosphate bond

3',5' phosphodiester 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 #135 : Identifying Biochemical Molecules

Atp

Identify the given nucleotide, nucleoside or nitrogenous base.

Possible Answers:

Adenosine-5-triphosphate

Adenine-5-triphosphate

Adenosine triphosphate

Adenosine-5-phosphate

Adenine 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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