MCAT Biology › DNA, RNA, and Proteins
If a gene has a sequence of 5'-AGCTGCCTT-3', what would be the complementary mRNA sequence that leaves the nucleus to be translated?
3'-UCGACGGAA-5'
5'-AGCTGCCTT-3'
3'-TCGACGGAA-5'
5'-UCGACGGAA-3'
5'-UCGUCGGAA-3'
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'
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.
Which intermediates of the central dogma of molecular biology below are present in normal cellular replication, but apparently absent in the above model of prion replication?
I. mRNA
II. tRNA
III. Protein
I and II
I and III
I, only
II, only
I, II, and III
The above reaction shows an actual transfer of information. The information contaiend in the specific structure of PrPC is converted to that contained in PrPRes; in other words, PrPRes is effectively replicating. In all other forms of cellular replication, based on the central dogma of molecular biology, replication occurs based on the following pattern:
Parental DNA → mRNA → Protein, carried by tRNA
Which of the following will be the complimentary pairing of this coded gene during transcription?
3’ GCTAGC 5’
5’ CGAUCG 3’
5’ CGATCG 3’
3’ CGATCG 5”
3’ CGAUCG 5’
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.
Which of the following experimental methods cannot be used to measure the relative abundance of a particular mRNA?
Western blot
Northern blot
Microarray
Reverse transcription polymerase chain reaction (rt-PCR)
Western blots are used to measure the relative abundance of proteins. While there is a correlation between the amount of mRNA and protein, using a western blot to measure mRNA would be inconclusive due to the variability of protein half life.
Northern blots are used to run mRNA samples on gels, DNA microarrys give the expression levels of certain genes, and rtPCR is used to detect RNA expression levels. Any of these methods could provide the relative abundance of a particular mRNA.
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.
Which intermediates of the central dogma of molecular biology below are present in normal cellular replication, but apparently absent in the above model of prion replication?
I. mRNA
II. tRNA
III. Protein
I and II
I and III
I, only
II, only
I, II, and III
The above reaction shows an actual transfer of information. The information contaiend in the specific structure of PrPC is converted to that contained in PrPRes; in other words, PrPRes is effectively replicating. In all other forms of cellular replication, based on the central dogma of molecular biology, replication occurs based on the following pattern:
Parental DNA → mRNA → Protein, carried by tRNA
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?
CGGACATGCTGG and GTTACCGCAGGC
ATCGCTTTGTAC and CGGACATGCTGG
ATCGCTTTGTAC and GTTACCGCAGGC
GTGTGATACCCC and CACACTATAAAA
CACACTATAAAA and ATCGCTTTGTAC
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).
Which of the following will be the complimentary pairing of this coded gene during transcription?
3’ GCTAGC 5’
5’ CGAUCG 3’
5’ CGATCG 3’
3’ CGATCG 5”
3’ CGAUCG 5’
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.
If a gene has a sequence of 5'-AGCTGCCTT-3', what would be the complementary mRNA sequence that leaves the nucleus to be translated?
3'-UCGACGGAA-5'
5'-AGCTGCCTT-3'
3'-TCGACGGAA-5'
5'-UCGACGGAA-3'
5'-UCGUCGGAA-3'
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'
Which of the following experimental methods cannot be used to measure the relative abundance of a particular mRNA?
Western blot
Northern blot
Microarray
Reverse transcription polymerase chain reaction (rt-PCR)
Western blots are used to measure the relative abundance of proteins. While there is a correlation between the amount of mRNA and protein, using a western blot to measure mRNA would be inconclusive due to the variability of protein half life.
Northern blots are used to run mRNA samples on gels, DNA microarrys give the expression levels of certain genes, and rtPCR is used to detect RNA expression levels. Any of these methods could provide the relative abundance of a particular mRNA.
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?
CGGACATGCTGG and GTTACCGCAGGC
ATCGCTTTGTAC and CGGACATGCTGG
ATCGCTTTGTAC and GTTACCGCAGGC
GTGTGATACCCC and CACACTATAAAA
CACACTATAAAA and ATCGCTTTGTAC
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).