Nucleic Acid Structures
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Biochemistry › Nucleic Acid Structures
Which of the following nitrogenous bases is a purine?
Adenine
Cytosine
Thymine
Uracil
Explanation
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.
Which of the following statements about B DNA are incorrect?
B DNA has a wide and deep major groove and a narrow and shallow minor groove
B DNA is the most commonly found double helical structure
B DNA is right handed with 10 base pairs per turn
B DNA has a diameter of
All of these are correct
Explanation
B DNA has a wide and deep major groove and a narrow and deep minor groove. All other statements regarding B DNA are true.
The backbone of a strand of DNA is comprised of which of these?
Sugars and phosphates
Sugars and nucleotides
Nucleotides and phosphates
Sugars only
Nucleotides only
Explanation
The backbone of DNA is made up of alternating phosphate groups and sugar groups, linked together via phosphodiester bonds. The nitrogenous bases jut off of the backbone and form bonds with nitrogenous bases on other strands of DNA to become double stranded. A nucleotide consists of a sugar, nitrogenous base, and one or more phosphate groups.
Which of the following statements about B DNA are incorrect?
B DNA has a wide and deep major groove and a narrow and shallow minor groove
B DNA is the most commonly found double helical structure
B DNA is right handed with 10 base pairs per turn
B DNA has a diameter of
All of these are correct
Explanation
B DNA has a wide and deep major groove and a narrow and deep minor groove. All other statements regarding B DNA are true.
The backbone of a strand of DNA is comprised of which of these?
Sugars and phosphates
Sugars and nucleotides
Nucleotides and phosphates
Sugars only
Nucleotides only
Explanation
The backbone of DNA is made up of alternating phosphate groups and sugar groups, linked together via phosphodiester bonds. The nitrogenous bases jut off of the backbone and form bonds with nitrogenous bases on other strands of DNA to become double stranded. A nucleotide consists of a sugar, nitrogenous base, and one or more phosphate groups.
Which of the following nitrogenous bases is a purine?
Adenine
Cytosine
Thymine
Uracil
Explanation
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.
The role of small nuclear RNA (snRNA) is to __________.
participate in the splicing of RNA exons
bind to complementary mRNA molecules to inhibit translation
carry amino acids to the ribosome for translation
bind to mRNA to facilitate its degradation
function as the template for protein synthesis
Explanation
The function of snRNA is to participate in the splicing of RNA exons. Micro RNA binds to complementary mRNA to inhibit translation. Small interfering RNA binds to mRNA to facilitate its degradation. mRNA functions as a template for protein synthesis. Transfer RNA (tRNA) carries amino acids to the ribosome during translation.
Two strands of DNA were isolated from a solution, named DNA-1 and DNA-2. DNA-2 was found to have a higher melting point (temperature at which the two strands break apart). What can we conclude about the two strands' nucleotide composition?
DNA-2 has a higher guanine and cytosine concentration
DNA-1 has a higher guanine and cytosine concentration
DNA-2 has a higher adenine and thymine concentration
DNA-1 has a higher adenine and thymine concentration
Explanation
Recall that guanine and cytosine form three hydrogen bonds to one another in DNA, while adenine and thymine only form two hydrogen bonds to one another. This means that DNA strands with higher concentrations of guanine and cytosine will be more stable, and thus require greater energy to break apart. In this case, since DNA-2 required more energy (higher temperature) to denature, it has a higher concentration of guanine and cytosine.
Generally, silencing of a gene is accomplished by __________?
Methylation
Acetylation
Decarboxylation
Ligation
Phosphorylation
Explanation
The silencing of a gene is most often accomplished via methylation of the DNA. The methyl groups are added to the gene's promoter region and thus, the DNA is not read by transcriptional enzymes.
Generally, silencing of a gene is accomplished by __________?
Methylation
Acetylation
Decarboxylation
Ligation
Phosphorylation
Explanation
The silencing of a gene is most often accomplished via methylation of the DNA. The methyl groups are added to the gene's promoter region and thus, the DNA is not read by transcriptional enzymes.