Nucleic Acid Structures and Functions - Biochemistry
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What is the role of xanthine oxidase?
I. The enzyme xanthine oxidase converts hypoxanthine to xanthine and, also, xanthine to uric acid.
II. Xanthine oxidase is involved in purine (nucleotides like adenine, guanine) degradation.
III. In diseases where there is a high production of purines, the enzyme's products (uric acid) can cause gout.
IV. Gout medication is designed to target xanthine oxidase.
What is the role of xanthine oxidase?
I. The enzyme xanthine oxidase converts hypoxanthine to xanthine and, also, xanthine to uric acid.
II. Xanthine oxidase is involved in purine (nucleotides like adenine, guanine) degradation.
III. In diseases where there is a high production of purines, the enzyme's products (uric acid) can cause gout.
IV. Gout medication is designed to target xanthine oxidase.
Xanthine oxidase is an enzyme important in purine catabolism. Nucleotides from DNA degradation are metabolized to uric acid by xanthine oxidase.In diseases with high levels of nucleotide production, uric acid levels are also high and produce symptoms of gout (uric acid is deposited abnormally in tissues). Gout is treated with inhibitors of xanthine oxidase such as allopurinol, reducing the levels of uric acid and the symptoms of gout.
Xanthine oxidase is an enzyme important in purine catabolism. Nucleotides from DNA degradation are metabolized to uric acid by xanthine oxidase.In diseases with high levels of nucleotide production, uric acid levels are also high and produce symptoms of gout (uric acid is deposited abnormally in tissues). Gout is treated with inhibitors of xanthine oxidase such as allopurinol, reducing the levels of uric acid and the symptoms of gout.
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Which statement concerning DNA methylation in mammals is false?
Which statement concerning DNA methylation in mammals is false?
Unmethylated cytosine spontaneously deaminates to uracil. Over time, methylated cytosine is spontaneously deaminated to thymine. Random deamination of methylcytosines causes mutation, creating hot spots. The vast majority of DNA methylations in mammals occurs at CpG (cytosine-phospate-guanine) sites.
Unmethylated cytosine spontaneously deaminates to uracil. Over time, methylated cytosine is spontaneously deaminated to thymine. Random deamination of methylcytosines causes mutation, creating hot spots. The vast majority of DNA methylations in mammals occurs at CpG (cytosine-phospate-guanine) sites.
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Which of the following describes a mutation in which a segment of DNA detaches from a chromosome and reattaches to another chromosome?
Which of the following describes a mutation in which a segment of DNA detaches from a chromosome and reattaches to another chromosome?
A null mutation is one that deactivates a gene entirely. Point mutations are those that occur within a single, small site in a gene. Inversion involves the reversal of orientation of a DNA segment. Deletion occurs when a whole part of a chromosome is removed, joining two ends that were far apart. Translocation involves the exchange of genetic material from two chromosomes that are not homologous.
A null mutation is one that deactivates a gene entirely. Point mutations are those that occur within a single, small site in a gene. Inversion involves the reversal of orientation of a DNA segment. Deletion occurs when a whole part of a chromosome is removed, joining two ends that were far apart. Translocation involves the exchange of genetic material from two chromosomes that are not homologous.
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Generally, silencing of a gene is accomplished by ?
Generally, silencing of a gene is accomplished by ?
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.
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.
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How does methylation cause the silencing of a gene?
How does methylation cause the silencing of a gene?
In order to silence a gene by methylation, methyl groups are added to the promoter region of DNA. This area is upstream of the coding sequence and is responsible for initiation of transcription. Thus, methylating the promoter region inhibits further transcription of the gene.
In order to silence a gene by methylation, methyl groups are added to the promoter region of DNA. This area is upstream of the coding sequence and is responsible for initiation of transcription. Thus, methylating the promoter region inhibits further transcription of the gene.
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Which of the following DNA bases can be methylated in the promoter region to silence a gene?
Which of the following DNA bases can be methylated in the promoter region to silence a gene?
The only two bases that can be methylated are cytosine and adenine.
The only two bases that can be methylated are cytosine and adenine.
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Formation of thymine dimers in DNA can lead to conditions such as melanoma when unrepaired. This DNA mutation is primarily caused by .
Formation of thymine dimers in DNA can lead to conditions such as melanoma when unrepaired. This DNA mutation is primarily caused by .
Alkylating agents and 
can also cause cancer, but they lead to methylation and mismatch mutations rather than the formation of pyrimidine dimers.
Alkylating agents and
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Which of the following statements about restriction enzymes is true?
Which of the following statements about restriction enzymes is true?
Reverse transcriptase synthesizes DNA in the 5' to 3' direction, using RNA as a template (hence it is the reverse of transcription). Restriction enzymes act only on DNA, not RNA, and they can cut bacterial as well as viral DNA—indeed, they can provide protection against viruses—and are found in archaea. Restriction enzymes can recognize specific sequences of nucleotides at restriction sites and cut DNA at these sites. Restriction enzymes do not create covalent bonds between adjacent exons after intron excision, rather this is done by tRNA splicing ligase.
Reverse transcriptase synthesizes DNA in the 5' to 3' direction, using RNA as a template (hence it is the reverse of transcription). Restriction enzymes act only on DNA, not RNA, and they can cut bacterial as well as viral DNA—indeed, they can provide protection against viruses—and are found in archaea. Restriction enzymes can recognize specific sequences of nucleotides at restriction sites and cut DNA at these sites. Restriction enzymes do not create covalent bonds between adjacent exons after intron excision, rather this is done by tRNA splicing ligase.
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What is the purpose of the pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS)?
What is the purpose of the pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS)?
The pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS), mainly serves to produce 
for anabolic reduction reactions and ribose-5-phosphate for nucleic acid production.
The pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS), mainly serves to produce
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Which of the following is an example of a nucleoside?
Which of the following is an example of a nucleoside?
A nucleoside is composed of both a nitrogenous base as well as a sugar. Cytosine and adenine are just nitrogenous bases. Guanosine monophosphate (or GMP) is also composed of a phosphate group, which designates it as a nucleotide. The only nucleoside is adenosine.
A nucleoside is composed of both a nitrogenous base as well as a sugar. Cytosine and adenine are just nitrogenous bases. Guanosine monophosphate (or GMP) is also composed of a phosphate group, which designates it as a nucleotide. The only nucleoside is adenosine.
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What is the role of xanthine oxidase?
I. The enzyme xanthine oxidase converts hypoxanthine to xanthine and, also, xanthine to uric acid.
II. Xanthine oxidase is involved in purine (nucleotides like adenine, guanine) degradation.
III. In diseases where there is a high production of purines, the enzyme's products (uric acid) can cause gout.
IV. Gout medication is designed to target xanthine oxidase.
What is the role of xanthine oxidase?
I. The enzyme xanthine oxidase converts hypoxanthine to xanthine and, also, xanthine to uric acid.
II. Xanthine oxidase is involved in purine (nucleotides like adenine, guanine) degradation.
III. In diseases where there is a high production of purines, the enzyme's products (uric acid) can cause gout.
IV. Gout medication is designed to target xanthine oxidase.
Xanthine oxidase is an enzyme important in purine catabolism. Nucleotides from DNA degradation are metabolized to uric acid by xanthine oxidase.In diseases with high levels of nucleotide production, uric acid levels are also high and produce symptoms of gout (uric acid is deposited abnormally in tissues). Gout is treated with inhibitors of xanthine oxidase such as allopurinol, reducing the levels of uric acid and the symptoms of gout.
Xanthine oxidase is an enzyme important in purine catabolism. Nucleotides from DNA degradation are metabolized to uric acid by xanthine oxidase.In diseases with high levels of nucleotide production, uric acid levels are also high and produce symptoms of gout (uric acid is deposited abnormally in tissues). Gout is treated with inhibitors of xanthine oxidase such as allopurinol, reducing the levels of uric acid and the symptoms of gout.
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What type of bonds are found between the DNA sugar hydroxyl groups? What are their corresponding carbon numbers?
What type of bonds are found between the DNA sugar hydroxyl groups? What are their corresponding carbon numbers?
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).
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).
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In DNA, the 5-carbon sugar is attached to the nitrogenous base by a .
In DNA, the 5-carbon sugar is attached to the nitrogenous base by a .
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.
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.
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Which of the following is not a reason that the anhydride linkage of pyrophosphate stores so much energy?
Which of the following is not a reason that the anhydride linkage of pyrophosphate stores so much energy?
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.
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.
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What type of bond holds the phosphate group to the sugar group in DNA's backbone?
What type of bond holds the phosphate group to the sugar group in DNA's backbone?
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.
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.
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What is the role of xanthine oxidase?
I. The enzyme xanthine oxidase converts hypoxanthine to xanthine and, also, xanthine to uric acid.
II. Xanthine oxidase is involved in purine (nucleotides like adenine, guanine) degradation.
III. In diseases where there is a high production of purines, the enzyme's products (uric acid) can cause gout.
IV. Gout medication is designed to target xanthine oxidase.
What is the role of xanthine oxidase?
I. The enzyme xanthine oxidase converts hypoxanthine to xanthine and, also, xanthine to uric acid.
II. Xanthine oxidase is involved in purine (nucleotides like adenine, guanine) degradation.
III. In diseases where there is a high production of purines, the enzyme's products (uric acid) can cause gout.
IV. Gout medication is designed to target xanthine oxidase.
Xanthine oxidase is an enzyme important in purine catabolism. Nucleotides from DNA degradation are metabolized to uric acid by xanthine oxidase.In diseases with high levels of nucleotide production, uric acid levels are also high and produce symptoms of gout (uric acid is deposited abnormally in tissues). Gout is treated with inhibitors of xanthine oxidase such as allopurinol, reducing the levels of uric acid and the symptoms of gout.
Xanthine oxidase is an enzyme important in purine catabolism. Nucleotides from DNA degradation are metabolized to uric acid by xanthine oxidase.In diseases with high levels of nucleotide production, uric acid levels are also high and produce symptoms of gout (uric acid is deposited abnormally in tissues). Gout is treated with inhibitors of xanthine oxidase such as allopurinol, reducing the levels of uric acid and the symptoms of gout.
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Which statement about the anticodon loop is false?
Which statement about the anticodon loop is false?
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.
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.
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The two pyrimidine bases, which have a one-ring nitrogenous base are and .
The two pyrimidine bases, which have a one-ring nitrogenous base are and .
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.
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.
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Which of the following statements concerning DNA nucleotides is true?
Which of the following statements concerning DNA nucleotides is true?
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.
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.
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What is the structural difference between thymine and uracil?
What is the structural difference between thymine and uracil?
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.
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.
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