DNA, RNA, and Proteins - MCAT Biological and Biochemical Foundations of Living Systems
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An important part of creating DNA primers when performing a PCR or other quantitative analysis is the melting point of the primer. Which set of primers would most likely work well together as the forward and reverse primers of a PCR?
An important part of creating DNA primers when performing a PCR or other quantitative analysis is the melting point of the primer. Which set of primers would most likely work well together as the forward and reverse primers of a PCR?
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The melting point of a strand of DNA can be predicted by the bases that make it up. Cytosine and guanine have three hydrogen bonds to each other, so they bond more strongly than adenine and thymine's two hydrogen bonds. This means that strands containing the same amount of Cs and Gs would work best together. There is only answer choice in which both strands have the same amount of Cs and Gs (or Ts and As).
The melting point of a strand of DNA can be predicted by the bases that make it up. Cytosine and guanine have three hydrogen bonds to each other, so they bond more strongly than adenine and thymine's two hydrogen bonds. This means that strands containing the same amount of Cs and Gs would work best together. There is only answer choice in which both strands have the same amount of Cs and Gs (or Ts and As).
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Which piece of DNA has the lowest melting point?
Note: only one strand is shown
Which piece of DNA has the lowest melting point?
Note: only one strand is shown
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Cytosine and guanine bond more strongly to each other than adenine and guanine because they have three hydrogen bonds as opposed to two. Therefore, a piece of DNA with a high concentration of Ts and As will have a low melting point. The correct choice has 8 Ts and As, while the rest have less than that.
Cytosine and guanine bond more strongly to each other than adenine and guanine because they have three hydrogen bonds as opposed to two. Therefore, a piece of DNA with a high concentration of Ts and As will have a low melting point. The correct choice has 8 Ts and As, while the rest have less than that.
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Which of the following will be the complimentary pairing of this coded gene during transcription?
3’ GCTAGC 5’
Which of the following will be the complimentary pairing of this coded gene during transcription?
3’ GCTAGC 5’
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During transcription, a complimentary RNA strand is constructed from a DNA template. It is important to realize that in RNA, the nucleotide base uracil is used instead of thymine as a complementary pair with adenine. The complementary strand is constructed 5’ to 3’ , but is lined up anti-parallel to the original strand.
During transcription, a complimentary RNA strand is constructed from a DNA template. It is important to realize that in RNA, the nucleotide base uracil is used instead of thymine as a complementary pair with adenine. The complementary strand is constructed 5’ to 3’ , but is lined up anti-parallel to the original strand.
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Which segment of DNA would have the highest melting point when paired with its complimentary strand?
Which segment of DNA would have the highest melting point when paired with its complimentary strand?
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DNA nucleotide base pairs are held together by hydrogen bonding. Cytosine and guanine are held together by three hydrogen bonds, where adenine and thymine are held together by only two. Increased hydrogen bonding within a strand of DNA will increase the melting point. The DNA segment with the most guanine-cytosine base pairs will have the highest melting point.
DNA nucleotide base pairs are held together by hydrogen bonding. Cytosine and guanine are held together by three hydrogen bonds, where adenine and thymine are held together by only two. Increased hydrogen bonding within a strand of DNA will increase the melting point. The DNA segment with the most guanine-cytosine base pairs will have the highest melting point.
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Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
The principal chemical component of chromosomes is nucleic acid, though proteins are also important elements. Which of the following is true of nucleic acids?
Human chromosomes are divided into two arms, a long q arm and a short p arm. A karyotype is the organization of a human cell’s total genetic complement. A typical karyotype is generated by ordering chromosome 1 to chromosome 23 in order of decreasing size.
When viewing a karyotype, it can often become apparent that changes in chromosome number, arrangement, or structure are present. Among the most common genetic changes are Robertsonian translocations, involving transposition of chromosomal material between long arms of certain chromosomes to form one derivative chromosome. Chromosomes 14 and 21, for example, often undergo a Robertsonian translocation, as below.
A karyotype of this individual for chromosomes 14 and 21 would thus appear as follows:
Though an individual with aberrations such as a Robertsonian translocation may be phenotypically normal, they can generate gametes through meiosis that have atypical organizations of chromosomes, resulting in recurrent fetal abnormalities or miscarriages.
The principal chemical component of chromosomes is nucleic acid, though proteins are also important elements. Which of the following is true of nucleic acids?
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Guanine-cytosine pairing forms three hydrogen bonds, instead of the two bonds formed by adenine and thymine. The other choices are all tempting, but subtly wrong. RNA contains uracil, DNA is the main storage form for information, mRNA is directly translated by tRNA, and ribosomes are important in the synthesis of proteins. It is worth noting that the 2' hydroxyl group of RNA's pentose sugar backbone is lost in DNA, which increases the stability and allows DNA to serve as a stable storage medium.
Guanine-cytosine pairing forms three hydrogen bonds, instead of the two bonds formed by adenine and thymine. The other choices are all tempting, but subtly wrong. RNA contains uracil, DNA is the main storage form for information, mRNA is directly translated by tRNA, and ribosomes are important in the synthesis of proteins. It is worth noting that the 2' hydroxyl group of RNA's pentose sugar backbone is lost in DNA, which increases the stability and allows DNA to serve as a stable storage medium.
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Which of the following options include degenerate codons?
Which of the following options include degenerate codons?
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The term "degenerate codons" refers to codons with different nucleotide base sequences that specify the same amino acid. In the provided examples, two codons (UCU and UCA) both specify serine, indicating this is the correct answer.
The term "degenerate codons" refers to codons with different nucleotide base sequences that specify the same amino acid. In the provided examples, two codons (UCU and UCA) both specify serine, indicating this is the correct answer.
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The codons GGU, GGA, GGC, and GGG all code for the same amino acid, glycine. What biological term is used to describe this phenomenon?
The codons GGU, GGA, GGC, and GGG all code for the same amino acid, glycine. What biological term is used to describe this phenomenon?
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Degeneracy refers to the fact that more than one codon can code for the same amino acid. These codons generally differ in their third or "wobble" base. Degeneracy explains how there can be a total of sixty-four possible codons corresponding to only twenty amino acids.
Degeneracy refers to the fact that more than one codon can code for the same amino acid. These codons generally differ in their third or "wobble" base. Degeneracy explains how there can be a total of sixty-four possible codons corresponding to only twenty amino acids.
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Pick the reason that is least likely to explain why two purines will never be seen attached to each other in a DNA helix.
Pick the reason that is least likely to explain why two purines will never be seen attached to each other in a DNA helix.
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DNA strands are composed of millions of nucleotides. As a result, it would be virtually impossible to find a single strand that did not have all four nucleotides.
Nucleotides combine in purine-pyrimidine pairs due to the sterically appropriate fit of the bases, as well as the preferred combination of hydrogen bonds between the two nucleotides. As a result, two purines would not be seen combined. This is due to both being too large when together, and the incorrect hydrigen bonding between their functional groups.
DNA strands are composed of millions of nucleotides. As a result, it would be virtually impossible to find a single strand that did not have all four nucleotides.
Nucleotides combine in purine-pyrimidine pairs due to the sterically appropriate fit of the bases, as well as the preferred combination of hydrogen bonds between the two nucleotides. As a result, two purines would not be seen combined. This is due to both being too large when together, and the incorrect hydrigen bonding between their functional groups.
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A sequence of DNA is written below.
5'-AGCCGTAAG-3'
What will be the squence of the strand created from this one by DNA polymerase during replication?
A sequence of DNA is written below.
5'-AGCCGTAAG-3'
What will be the squence of the strand created from this one by DNA polymerase during replication?
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Remember that DNA polymerase builds the new strand by reading the original DNA strand in a 3' to 5' direction. The newly formed strand will be read 5' to 3' and will have nucleotides that are complementary to the original strand.
Remember that DNA polymerase builds the new strand by reading the original DNA strand in a 3' to 5' direction. The newly formed strand will be read 5' to 3' and will have nucleotides that are complementary to the original strand.
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In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:
In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.
During translation, the genetic code is used to convert a sequence of nitrogenous bases in mRNA to an amino acid sequence. Which of the following is true of the genetic code?
I. More than one codon sequence codes for a single amino acid
II. The most 5' position of the codon on mRNA is the wobble position
III. Each codon sequence only codes for one amino acid
In 2013, scientists linked a cellular response called the unfolded protein response (UPR) to a series of neurodegenerative diseases, including such major health issues as Parkinson’s and Alzheimer’s Disease. According to their work, the unfolded protein response is a reduction in translation as a result of a series of enzymes that modify a translation initiation factor, eIF2, as below:
In the above sequence, the unfolded protein sensor binds to unfolded protein, such as the pathogenic amyloid-beta found in the brains of Alzheimer’s Disease patients. This sensor then phosphorylates PERK, or protein kinase RNA-like endoplasmic reticulum kinase. This leads to downstream effects on eIF2, inhibition of which represses translation. It is thought that symptoms of neurodegenerative disease may be a result of this reduced translation.
During translation, the genetic code is used to convert a sequence of nitrogenous bases in mRNA to an amino acid sequence. Which of the following is true of the genetic code?
I. More than one codon sequence codes for a single amino acid
II. The most 5' position of the codon on mRNA is the wobble position
III. Each codon sequence only codes for one amino acid
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The genetic code is unambiguous, because each codon only codes for one amino acid. It is also degenerate, so that each amino acid can be coded for by multiple codons. Choice 2 is incorrect, as the most 3' position on the mRNA is the wobble position.
The genetic code is unambiguous, because each codon only codes for one amino acid. It is also degenerate, so that each amino acid can be coded for by multiple codons. Choice 2 is incorrect, as the most 3' position on the mRNA is the wobble position.
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What is the mRNA transcript of the given DNA sequence?
3' ACCTGTTAC 5'
What is the mRNA transcript of the given DNA sequence?
3' ACCTGTTAC 5'
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mRNA is transcribed antiparallel to the DNA template, meaning that the 5' end of the mRNA sequence should align with the 3' end of the DNA sequence. Pairing rules dictate that cytosine will pair with guanine and adenine with uracil, rather than thymine. Using these conventions, we can decipher the mRNA sequence that correlates to the given DNA template.
DNA: 3' ACCTGTTAC 5'
RNA: 5' UGGACAAUG 3'
mRNA is transcribed antiparallel to the DNA template, meaning that the 5' end of the mRNA sequence should align with the 3' end of the DNA sequence. Pairing rules dictate that cytosine will pair with guanine and adenine with uracil, rather than thymine. Using these conventions, we can decipher the mRNA sequence that correlates to the given DNA template.
DNA: 3' ACCTGTTAC 5'
RNA: 5' UGGACAAUG 3'
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If a gene has a sequence of 5'-AGCTGCCTT-3', what would be the complementary mRNA sequence that leaves the nucleus to be translated?
If a gene has a sequence of 5'-AGCTGCCTT-3', what would be the complementary mRNA sequence that leaves the nucleus to be translated?
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The correct answer is 3'-UCGACGGAA-5'.
In order to arrive at this answer, it is important to note that we are starting with DNA and finding the complementary mRNA. We must remember that there is no thymine in RNA; instead of thymine, RNA has uracil. The last thing to remember is that the mRNA strand will be anti-parallel, meaning that the 5' end of the DNA sequence must match up with the 3' end of the RNA sequence. Cytosine and guanine will form pairs. Adenine bases in DNA will pair to uracil bases in RNA, and thymine bases in DNA will bind to adenine in RNA.
DNA: 5'-AGCTGCCTT-3'
RNA: 3'-UCGACGGAA-5'
The correct answer is 3'-UCGACGGAA-5'.
In order to arrive at this answer, it is important to note that we are starting with DNA and finding the complementary mRNA. We must remember that there is no thymine in RNA; instead of thymine, RNA has uracil. The last thing to remember is that the mRNA strand will be anti-parallel, meaning that the 5' end of the DNA sequence must match up with the 3' end of the RNA sequence. Cytosine and guanine will form pairs. Adenine bases in DNA will pair to uracil bases in RNA, and thymine bases in DNA will bind to adenine in RNA.
DNA: 5'-AGCTGCCTT-3'
RNA: 3'-UCGACGGAA-5'
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A short polynucleotide strand with the base sequence of AUCCCUGG must be .
A short polynucleotide strand with the base sequence of AUCCCUGG must be .
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Polynucleotide sequences are nucleic acids, so they must be DNA or RNA. Any sequence containing U (uracil) must be RNA, however there is no way to determine the type of RNA simply by looking at the sequence. This sequence could code for mRNA, rRNA, or tRNA.
mRNA is used to translate proteins. rRNA plays a structural and functional role in composing ribosomes. tRNA carries amino acids to the ribosome during translation.
Polynucleotide sequences are nucleic acids, so they must be DNA or RNA. Any sequence containing U (uracil) must be RNA, however there is no way to determine the type of RNA simply by looking at the sequence. This sequence could code for mRNA, rRNA, or tRNA.
mRNA is used to translate proteins. rRNA plays a structural and functional role in composing ribosomes. tRNA carries amino acids to the ribosome during translation.
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Which of the following correctly arranges the bases on the anti-codon loop of a tRNA carrying tryptophan?
Tryptophan codon: 3'-UGG-5'
Which of the following correctly arranges the bases on the anti-codon loop of a tRNA carrying tryptophan?
Tryptophan codon: 3'-UGG-5'
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Tryptophan, which is encoded on mRNA as 3'-UGG-5', is going to be transported to the ribosome via tryptophan t-RNA. The anti-codon loop must be complementary to the mRNA strand. Since the code for Tryptophan is 3'-UGG-'5, the anti-codon loop of the t-RNA must read 3'-CCA-5' in order to line up.
mRNA: 3'-UGG-'5
tRNA: 5'-ACC-3'
Tryptophan, which is encoded on mRNA as 3'-UGG-5', is going to be transported to the ribosome via tryptophan t-RNA. The anti-codon loop must be complementary to the mRNA strand. Since the code for Tryptophan is 3'-UGG-'5, the anti-codon loop of the t-RNA must read 3'-CCA-5' in order to line up.
mRNA: 3'-UGG-'5
tRNA: 5'-ACC-3'
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You are a student researcher cloning a gene that is around 1500 bases long into a vector for recombinant expression. Starting with cDNA, you succesfully clone and transfect bacterial cells to propogate the plasmid. You sequence the plasmid to check and make sure that the target gene has been succesfully incoorporated into the vector. After checking the sequence, you notice that there is a single nucleotide that has been switched from an A to a G several hundred basepairs after the start codon. You express the protein anyway. After subjecting the protein to SDS-page, you learn that it exists at its expected length, but in a functional asssay, the protein seems to have lost its function. What type of mutation is this called?
You are a student researcher cloning a gene that is around 1500 bases long into a vector for recombinant expression. Starting with cDNA, you succesfully clone and transfect bacterial cells to propogate the plasmid. You sequence the plasmid to check and make sure that the target gene has been succesfully incoorporated into the vector. After checking the sequence, you notice that there is a single nucleotide that has been switched from an A to a G several hundred basepairs after the start codon. You express the protein anyway. After subjecting the protein to SDS-page, you learn that it exists at its expected length, but in a functional asssay, the protein seems to have lost its function. What type of mutation is this called?
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Nonsense mutations result in a premature stop codon, which would have resulted in a shorter peptide. A silent mutation means that there is a change in the nucleotide sequence, but not in the amino acid sequence. Thus, this is not likely the case seeing as there is a loss of function in the cloned and recombinantly expressed protein. We have no reason to believe that a frameshift mutation occurred. Rather, what the student observed was a point mutation that resulted in a missense reading of the gene.
Nonsense mutations result in a premature stop codon, which would have resulted in a shorter peptide. A silent mutation means that there is a change in the nucleotide sequence, but not in the amino acid sequence. Thus, this is not likely the case seeing as there is a loss of function in the cloned and recombinantly expressed protein. We have no reason to believe that a frameshift mutation occurred. Rather, what the student observed was a point mutation that resulted in a missense reading of the gene.
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Which statement best describes the function of the enzyme DNA helicase?
Which statement best describes the function of the enzyme DNA helicase?
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DNA helicases are enzymes that separate the two DNA strands, and unwinds them as it progresses along the helix. It functions much like a zipper unwinding the DNA.
DNA helicases are enzymes that separate the two DNA strands, and unwinds them as it progresses along the helix. It functions much like a zipper unwinding the DNA.
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Prions are the suspected cause of a wide variety of neurodegenerative diseases in mammals. According to prevailing theory, prions are infectious particles made only of protein and found in high concentrations in the brains of infected animals. All mammals produce normal prion protein, PrPC, a transmembrane protein whose function remains unclear.
Infectious prions, PrPRes, induce conformational changes in the existing PrPC proteins according to the following reaction:
PrPC + PrPRes → PrPRes + PrPRes
The PrPRes is then suspected to accumulate in the nervous tissue of infected patients and cause disease. This model of transmission generates replicated proteins, but does so bypassing the standard model of the central dogma of molecular biology. Transcription and translation apparently do not play a role in this replication process.
This theory is a major departure from previously established biological dogma. A scientist decides to test the protein-only theory of prion propagation. He establishes his experiment as follows:
Homogenized brain matter of infected rabbits is injected into the brains of healthy rabbits, as per the following table:
Rabbit 1 and 2: injected with normal saline on days 1 and 2
The above trials serve as controls.
Rabbit 3 and 4: injected with homogenized brain matter on days 1 and 2
The above trials use unmodified brain matter.
Rabbit 5 and 6: injected with irradiated homogenized brain matter on days 1 and 2
The above trials use brain matter that has been irradiated to destroy nucleic acids in the homogenate.
Rabbit 7 and 8: injected with protein-free centrifuged homogenized brain matter on days 1 and 2
The above trials use brain matter that has been centrifuged to generate a protein-free homogenate and a protein-rich homogenate based on molecular weight.
Rabbit 9 and 10: injected with boiled homogenized brain matter on days 1 and 2
The above trials use brain matter that have been boiled to destroy any bacterial contaminants in the homogenate.
In the material used with Rabbits 5 and 6, irradiation was used to destroy DNA. In functioning, normal cells, what types of genes typically code for DNA repair proteins?
I. Tumor suppresor genes
II. Proto-onco genes
III. Pro-apoptotic genes
Prions are the suspected cause of a wide variety of neurodegenerative diseases in mammals. According to prevailing theory, prions are infectious particles made only of protein and found in high concentrations in the brains of infected animals. All mammals produce normal prion protein, PrPC, a transmembrane protein whose function remains unclear.
Infectious prions, PrPRes, induce conformational changes in the existing PrPC proteins according to the following reaction:
PrPC + PrPRes → PrPRes + PrPRes
The PrPRes is then suspected to accumulate in the nervous tissue of infected patients and cause disease. This model of transmission generates replicated proteins, but does so bypassing the standard model of the central dogma of molecular biology. Transcription and translation apparently do not play a role in this replication process.
This theory is a major departure from previously established biological dogma. A scientist decides to test the protein-only theory of prion propagation. He establishes his experiment as follows:
Homogenized brain matter of infected rabbits is injected into the brains of healthy rabbits, as per the following table:
Rabbit 1 and 2: injected with normal saline on days 1 and 2
The above trials serve as controls.
Rabbit 3 and 4: injected with homogenized brain matter on days 1 and 2
The above trials use unmodified brain matter.
Rabbit 5 and 6: injected with irradiated homogenized brain matter on days 1 and 2
The above trials use brain matter that has been irradiated to destroy nucleic acids in the homogenate.
Rabbit 7 and 8: injected with protein-free centrifuged homogenized brain matter on days 1 and 2
The above trials use brain matter that has been centrifuged to generate a protein-free homogenate and a protein-rich homogenate based on molecular weight.
Rabbit 9 and 10: injected with boiled homogenized brain matter on days 1 and 2
The above trials use brain matter that have been boiled to destroy any bacterial contaminants in the homogenate.
In the material used with Rabbits 5 and 6, irradiation was used to destroy DNA. In functioning, normal cells, what types of genes typically code for DNA repair proteins?
I. Tumor suppresor genes
II. Proto-onco genes
III. Pro-apoptotic genes
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Tumor suppresor genes, like p53 and Rb, usually code for DNA repair enzymes. Proto-oncogenes typically code for cell growth factors or receptors, and pro-apoptotic proteins would not lead to DNA repair, but would prevent tumor development via cell death pathways.
Tumor suppresor genes, like p53 and Rb, usually code for DNA repair enzymes. Proto-oncogenes typically code for cell growth factors or receptors, and pro-apoptotic proteins would not lead to DNA repair, but would prevent tumor development via cell death pathways.
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A culture of human tissue is being grown in a lab to study mitosis. A solution containing radioactively labelled cytosines was added to the culture in the middle of prophase, and then growth was halted at the end of telophase. Where would the scientists see radioactively labelled DNA?
A culture of human tissue is being grown in a lab to study mitosis. A solution containing radioactively labelled cytosines was added to the culture in the middle of prophase, and then growth was halted at the end of telophase. Where would the scientists see radioactively labelled DNA?
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DNA is replicated in S phase. Prophase is a part of mitosis, or M phase. Since all of the DNA that would be present at the end of telophase had already been synthesized in S phase, none of the radioactively labelled cytosines would be incorporated into the DNA of any cells in the culture.
DNA is replicated in S phase. Prophase is a part of mitosis, or M phase. Since all of the DNA that would be present at the end of telophase had already been synthesized in S phase, none of the radioactively labelled cytosines would be incorporated into the DNA of any cells in the culture.
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Which answer choice correctly matches the molecule with its function in DNA replication?
Which answer choice correctly matches the molecule with its function in DNA replication?
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Topoisomerase functions to untangle the supercoiling of DNA, which is when DNA overwinds into itself. This mechanism facilitates the unwinding action of helicase during replication. Single-stranded binding proteins bind to the two unzipped DNA strands to prevent them from prematurely coming back together into a whole molecule; otherwise replication would be interrupted.
The other proteins discussed serve the following functions.
Polymerase—adds nucleotides to new strands
Primase—adds RNA primers prior to replication
DNase—cleaves and degrades DNA molecules
Topoisomerase functions to untangle the supercoiling of DNA, which is when DNA overwinds into itself. This mechanism facilitates the unwinding action of helicase during replication. Single-stranded binding proteins bind to the two unzipped DNA strands to prevent them from prematurely coming back together into a whole molecule; otherwise replication would be interrupted.
The other proteins discussed serve the following functions.
Polymerase—adds nucleotides to new strands
Primase—adds RNA primers prior to replication
DNase—cleaves and degrades DNA molecules
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Which of the following is the first to act during DNA replication?
Which of the following is the first to act during DNA replication?
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Helicase is the first component of the DNA replication machinery to act during replication. It works by "unzipping" the double-stranded DNA so that replication can subsequently occur. Following the work of helicase, primase creates a primer to which the DNA polymerase will subsequently add deoxynucleotides and elongate the strand. DNA ligase acts at the end of replication by joining together the Okazaki fragments of the lagging strand.
Helicase is the first component of the DNA replication machinery to act during replication. It works by "unzipping" the double-stranded DNA so that replication can subsequently occur. Following the work of helicase, primase creates a primer to which the DNA polymerase will subsequently add deoxynucleotides and elongate the strand. DNA ligase acts at the end of replication by joining together the Okazaki fragments of the lagging strand.
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