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Example Questions
Example Question #1 : Sugar Phosphate Groups And Phosphodiester Bonds
What type of bonds are found between the DNA sugar hydroxyl groups? What are their corresponding carbon numbers?
Phosphodiester; 2', 4'
Phosphodiester; 1', 3'
Phosphodiester; 3', 5'
Phosphoester; 3', 5'
Phosphoester; 1', 5'
Phosphodiester; 3', 5'
The phosphodiester bonds in DNA occur between the 3' and 5' hydroxyl groups on deoxyribose. (This is related to DNA's 5' to 3' directionality as DNA polymerase can only synthesize DNA by adding nucleotides to the 3' hydroxyl group).
Example Question #1 : Sugar Phosphate Groups And Phosphodiester Bonds
In DNA, the 5-carbon sugar is attached to the nitrogenous base by a __________.
phosphoester bond
glycosidic bond
phosphodiester bond
ester
deoxyribose
glycosidic bond
The beta-N-glycosidic bond attaches the nitrogen on the purine or pyrimidine base to the 1' anomeric carbon on the deoxyribose sugar. Phosphodiester linkages connect the 3' and 5' sugar hydroxyl groups on adjacent nucleotides.
Example Question #1 : Sugar Phosphate Groups And Phosphodiester Bonds
Which of the following is not a reason that the anhydride linkage of pyrophosphate stores so much energy?
Orthophosphate by itself has more favorable interactions with water than two orthophosphates linked together (pyrophosphate).
All of the choices are true
Pyrophosphate has less resonance forms than orthophosphate groups by themselves.
Phosphorus on pyrophosphate satisfies the octet rule, but does not on orthophosphate.
The negative charges on the on the orthophosphates repel each other.
Phosphorus on pyrophosphate satisfies the octet rule, but does not on orthophosphate.
Phosphorus on both orthophosphate and pyrophosphate is surrounded by 10 electrons. This does not satisfy the octet rule in either case, so that answer choice is false, and therefore the correct answer. With four negative charges close by, pyrophosphate is very unstable, and releases a lot of energy when cleaved. Finally, the two orthophosphates formed from a single pyrophosphate gain an additional resonance structure.
Example Question #1 : Sugar Phosphate Groups And Phosphodiester Bonds
What type of bond holds the phosphate group to the sugar group in DNA's backbone?
Hydrogen bond
Glycosidic bond
Phosphodiester bond
Ionic bond
Covalent bond
Phosphodiester bond
The type of bond that holds the phosphate group to the sugar in DNA's backbone is called a phosphodiester bond. Hydrogen bonds connect bases to one another and glycosidic bonds occur between deoxyribose groups and the base groups.
Example Question #1 : Nitrogenous Bases
Which statement about the anticodon loop is false?
None of the other statements is false.
Anticodons are antiparallel to their corresponding mRNA codon.
An anticodon with guanine in position one can appear with any other of the four codons to code for the same amino acid.
The anticodon sequence is located on a tRNA hairpin loop.
One possible base in position one of the anticodon is hypoxanthine.
An anticodon with guanine in position one can appear with any other of the four codons to code for the same amino acid.
The type of loop of tRNA at the anticodon sequence is indeed hairpin. Hypoxanthine is occasionally found in tRNA anticodons (as its nucleoside, inosine). tRNA anticodons and mRNA codons are indeed antiparallel (this is central to their functioning). However, just because an anticodon has guanine in position one, doesn’t mean in cannot code with any of the four codons to make the same amino acid; the amino acid produced will be subject to whatever combination of bases is present, as detailed in the genetic code.
Example Question #1 : Nucleic Acid Structures
The two pyrimidine bases, which have a one-ring nitrogenous base are __________ and __________.
cytosine . . . guanine
adenine . . . guanine
adenine . . . thymine
cytosine . . . thymine
thymine . . . guanine
cytosine . . . thymine
The two pyrimidine bases are cytosine and thymine. Purine bases are larger in structure than pyrimidines and possess a two-ring nitrogenous base. In RNA, uracil is also a pyrimidine. One way to help us remember which nitrogenous bases are which is to use the mnemonic CUT. Pyramids (like pyrimidines) are "sharp" and thus they CUT, Cytosine, Uracil and Thymine.
Example Question #3 : Nitrogenous Bases
Which of the following statements concerning DNA nucleotides is true?
The structure of adenine is identical to guanine with the exception of one additional amino group on carbon #2
All DNA nucleotides have tautomeric forms, and the lactim or enol form is more common
Pyrimidines have a larger structure than purines
The structure of thymine is identical to cytosine with the exception of one additional methyl group on carbon #5
DNA nucleotides have a maximum absorbance at
The structure of thymine is identical to cytosine with the exception of one additional methyl group on carbon #5
DNA nucleotides have a maximum absorbance at 280 260nm. Pyrimidines Purines have a larger structure than purines pyrimidines, since purines have two rings in their structures, and the pyrimidines have only one. All DNA nucleotides have tautomeric forms, and the lactim or enol lactam or keto form is more common. The structure of adenine is identical to guanine with the exception of one additional amino group on carbon #2 and a double bonded oxygen replacing the amino group on carbon #6.
Example Question #2 : Nucleic Acid Structures
What is the structural difference between thymine and uracil?
Thymine has an amino group on the 5' carbon while uracil has a methyl group at this location
Thymine has a methyl group on the 5' carbon where uracil has no substitution on this carbon
Uracil has a methyl group at the 5' carbon while thymine has a carbonyl group at this location
Uracil has a methyl group on the 5' carbon where thymine has no substitution on this carbon
Uracil has an amino group at the 5' carbon while thymine has a methyl group at this location
Thymine has a methyl group on the 5' carbon where uracil has no substitution on this carbon
Thymine and uracil a both pyrimidines with similar structure but a key difference at the 5' carbon. While this location is methylated in thymine, there is no functional group there in uracil.
Example Question #3 : Nucleic Acid Structures
Which of these is a purine?
Thymine
Uracil
Ribulose
Adenine
Cytosine
Adenine
Adenine and guanine are purines (contain two rings). Thymine, cytosine, and uracil are pyrimidines (contain one ring). In normal base pairing, a purine matches to a pyrimidine. Adenine matches to thymine in DNA (uracil in RNA), and cytosine matches to guanine. Ribulose is a carbohydrate.
Example Question #6 : Nitrogenous Bases
Which of the following nitrogenous bases is a purine?
Uracil
Cytosine
Adenine
Thymine
Adenine
In DNA and RNA, there are two types of nitrogenous bases: pyrimidines and purines. A pyrimidine contains one carbon-nitrogen ring with two nitrogen atoms. A purine consists of a pyrimidine fused with an imidazole ring. Adenine and guanine are purines. Cytosine, thymine, and uracil are pyrimidines.
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