Biochemistry : Identifying Specific Nucleic Acid Structures
Study concepts, example questions & explanations for Biochemistry
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Example Questions
Example Question #1 : Identifying Specific Nucleic Acid Structures
Identify the nucleobase.
Cytosine
Uracil
Adenine
Guanine
Thymine
Guanine
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.
Cytosine
Adenine
Thymine
Uracil
Guanine
Adenine
The structure is adenine because of the characteristic amine group on carbon 6 and lack of any other substituents.
Example Question #2 : Identifying Specific Nucleic Acid Structures
Identify the nucleobase.
Adenine
Uracil
Guanine
Cytosine
Thymine
Thymine
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 #3 : Identifying Specific Nucleic Acid Structures
Identify the nucleobase.
Thymine
Cytosine
Uracil
Guanine
Adenine
Uracil
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 #4 : Identifying Specific Nucleic Acid Structures
Identify the nucleobase.
Guanine
Cytosine
Adenine
Uracil
Thymine
Cytosine
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 #1 : Identifying Specific Nucleic Acid Structures
Which of the following are considered pyrimidines?
I: adenine
II: thymine
III: cytosine
IV: guanine
III and IV
I and III
II and III
I and IV
I and II
II and III
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 #5 : Identifying Specific Nucleic Acid Structures
Name the given ring systems and determine whether they are soluble or insoluble.
Amine ring; insoluble
Pyrimidine ring; purine ring; insoluble
Pyrimidine ring; purine ring; soluble
Purine ring; pyrimidine ring; insoluble
Cytosine; adenine,; soluble
Pyrimidine ring; purine ring; insoluble
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 #6 : Identifying Specific Nucleic Acid Structures
What is the name of the molecule shown?
Cytidine
Pyrimidine
Uracil
Thymine
Cytosine
Cytosine
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
Identify the given nucleotide, nucleoside or nitrogenous base.
Adenosine
Purine
Adenine
Guanine
Guanosine
Adenosine
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 #3 : Identifying Specific Nucleic Acid Structures
Identify the given nucleotide, nucleoside or nitrogenous base.
Guanosine phosphate
Guanine phosphate
Guanosine-5-monophosphate
Guanine monophosphate
Guanosine monophosphate
Guanosine-5-monophosphate
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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