Biochemistry : Identifying Specific Nucleic Acid Structures
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Example Questions
Example Question #11 : Identifying Specific Nucleic Acid Structures
Identify the given nucleotide, nucleoside or nitrogenous base.
Uracine
Uracil
Thymidine
Thymine
Uridine
Uracil
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
Identify the given nucleotide, nucleoside or nitrogenous base.
Purine
Adenine
Guanine
Adenosine
Guanosine
Adenine
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 #13 : Identifying Specific Nucleic Acid Structures
Identify the given nucleotide, nucleoside or nitrogenous base.
Guanine
Purine
Adenine
Guanosine
Adenosine
Guanine
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 #14 : Identifying Specific Nucleic Acid Structures
Identify the given nucleotide, nucleoside or nitrogenous base.
Thymidine
Uracil
Thymine
Pyrimidine
Cytosine
Thymine
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 #15 : Identifying Specific Nucleic Acid Structures
Which of the following nitrogenous bases is found exclusively in DNA?
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 #16 : Identifying Specific Nucleic Acid Structures
Describe the bond indicated by the box in the given figure.
5',3' phosphodiester bond
3',5' phosphodiester bond
3',5' phosphoester bond
3',5' phosphate bond
5',3' phosphoester bond
3',5' phosphodiester bond
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 #17 : Identifying Specific Nucleic Acid Structures
Identify the given nucleotide, nucleoside or nitrogenous base.
Adenosine triphosphate
Adenosine-5-phosphate
Adenosine-5-triphosphate
Adenine-5-triphosphate
Adenine triphosphate
Adenosine-5-triphosphate
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 #18 : Identifying Specific Nucleic Acid Structures
Identify the given nucleotide, nucleoside or nitrogenous base.
Cytidine
Deoxycytidine
Cytosine
Uridine
Adenosine
Cytidine
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 
Example Question #19 : Identifying Specific Nucleic Acid Structures
Which of the following composes nucleotides?
Pentose, nitrogenous base, phosphate
Nitrogenous base, phosphate, glucose
Purines, pyrimidines, pentose, nucleotide base
Phosphate, nitrogenous base, fructose
Ribose, nitrogenous base, phosphate
Pentose, nitrogenous base, phosphate
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 #20 : Identifying Specific Nucleic Acid Structures
Which of the following nucleic acid bases is not in the right category?
Guanine - purine
Thymine - pyrimidine
Cytosine - pyrimidine
Uracil - purine
Adenine - purine
Uracil - purine
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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