PCB 3023 Exam 3 | UPDATED Questions with 100% Verified Answers
Question:
Restriction enzymes cut DNA
Answer:
at a specific sequence, whether in cells or in a test tube
FEEDBACK: Restriction enzymes are enzymes that recognize and cut specific sequences.
While matching sequences are protected in the host bacterium's genome, this is an
effective way to cleave any DNA of foreign origin. Restriction enzymes are widely used in
laboratories to cut DNA at a specific sequence, regardless of DNA's origin.
Question:
DNA migrates through the pores of an agarose gel towards
the ________ electrode; larger fragments travel more________.
Answer:
positive; slowly
FEEDBACK:
DNA fragments can be separated by size by forcing their migration through a dense gel
matrix; the larger fragments are slower to migrate because they are impeded by the
matrix. The DNA fragments move toward the positive electrode due to their negative
charge generated by the phosphate groups in the molecule's backbone.
Question:
DNA in a gel is most often visualized by
Answer:
staining with a UV-reactive dye.
FEEDBACK:
DNA itself is colorless under visible light or blacklight. The DNA bands are visualized by
adding a UV-reactive dye that interacts between bases of DNA molecules and observing
under UV light.
Question:
Which feature of a cloning vector enables bacterial cells to
replicate a plasmid to make many more copies?
, Answer:
replication origin
FEEDBACK: For a piece of DNA to be replicated by the cell's machinery, it requires a
replication origin, which is a sequence recognized by the cell for the cellular polymerase
and other replication enzymes, in order to begin the copying process. Investigators take
advantage of this phenomenon to isolate many copies of a desired plasmid.
Question:
A genomic library is a collection of plasmids, each containing
different chromosomal fragments from the genome of an
organism. A cDNA library, on the other hand, contains only the
________ genome of an organism.
Answer:
coding sequences of genes
FEEDBACK: A cDNA library is a library of DNA fragments that are made from reverse
transcription of mRNA transcripts. This type of library contains only the coding sequences
of each gene, since introns are spliced out of mature mRNAs.
Question:
The first step of PCR requires that the DNA to be amplified is
Answer:
denatured.
FEEDBACK: In PCR, the target DNA must first be heated to denature the molecule into
single-stranded DNA. This allows the primers to bind in the second step by base-pairing
with their complementary sequence.
Question:
Approximately how many double-stranded DNA molecules
will be formed from one starting molecule after three rounds
of PCR?
Answer:
8
FEEDBACK: After the first cycle of a PCR reaction, each starting target DNA molecule
serves as the template for generating two new daughter molecules, comparable to DNA
,replication in cell. The second cycle will then duplicate each of the molecules from the
first cycle, producing four total molecules, and the third cycle duplicates each of those
four molecules into eight.
Question:
The DNA polymerase enzyme used in PCR is different from
the one used in human cells because it is able to
Answer:
withstand the high temperatures needed for denaturation.
FEEDBACK: PCR uses a polymerase that was isolated from a thermophilic bacterium. This
enzyme can withstand the high heat needed to denature the DNA strands in step one of
PCR.
Question:
The chain-termination method of sequencing relies on the
formation of partial copies of the DNA fragment that terminate
at each position in the sequence. The fragments are separated
by size and the terminating nucleotide is identified by
Answer:
the position in the capillary and a unique fluorescent tag on each nucleotide.
FEEDBACK: The chain-termination method of sequencing (or Sanger sequencing)
amplifies the DNA of interest to form many molecules that are randomly terminated by
the incorporation of one of four different fluorescently labeled dideoxynucleotides. The
fragments are separated by size in a capillary gel matrix and the fluorescent tags are
read to reveal the sequence of the DNA molecule.
Question:
The CRISPR system can be used to activate a gene by altering
the Cas9 enzyme in what way?
Answer:
fusing an inactive Cas9 to a transcriptional activator
FEEDBACK: Instead of targeting a Cas9 nuclease to a site for making a double-strand
break for genome editing, CRISPR can be used to target various activities to specific
, locations in the genome. This is done by inactivating the Cas9 so that it is no longer a
nuclease, and then attaching a protein with a desired activity.
Question:
Shown here is an expression vector. For the gene of interest to
be expressed in the cells, the gene of interest must be cloned
where in this vector?
Answer:
next to the promoter, in the proper orientation
FEEDBACK: Expression vectors contain a promoter that drives transcription of the gene
of interest. Promoters have directionality, so for the gene to be expressed, the gene must
be placed in the proper location relative to the promoter.
Question:
If a protein with a specific activity is isolated, how can the
encoding gene be identified?
Answer:
It can be identified by mass spectrometry followed by gene database searching.
FEEDBACK: Proteins of interest can be identified using mass spectrometry to determine
many short amino acid sequences read from the protein. These sequences can then be
compared to a database of all known protein-coding genes to identify the gene that
encodes this protein.
Question:
Gel electrophoresis separates DNA fragments from each
other by virtue of which feature?
Answer:
Question:
Restriction enzymes cut DNA
Answer:
at a specific sequence, whether in cells or in a test tube
FEEDBACK: Restriction enzymes are enzymes that recognize and cut specific sequences.
While matching sequences are protected in the host bacterium's genome, this is an
effective way to cleave any DNA of foreign origin. Restriction enzymes are widely used in
laboratories to cut DNA at a specific sequence, regardless of DNA's origin.
Question:
DNA migrates through the pores of an agarose gel towards
the ________ electrode; larger fragments travel more________.
Answer:
positive; slowly
FEEDBACK:
DNA fragments can be separated by size by forcing their migration through a dense gel
matrix; the larger fragments are slower to migrate because they are impeded by the
matrix. The DNA fragments move toward the positive electrode due to their negative
charge generated by the phosphate groups in the molecule's backbone.
Question:
DNA in a gel is most often visualized by
Answer:
staining with a UV-reactive dye.
FEEDBACK:
DNA itself is colorless under visible light or blacklight. The DNA bands are visualized by
adding a UV-reactive dye that interacts between bases of DNA molecules and observing
under UV light.
Question:
Which feature of a cloning vector enables bacterial cells to
replicate a plasmid to make many more copies?
, Answer:
replication origin
FEEDBACK: For a piece of DNA to be replicated by the cell's machinery, it requires a
replication origin, which is a sequence recognized by the cell for the cellular polymerase
and other replication enzymes, in order to begin the copying process. Investigators take
advantage of this phenomenon to isolate many copies of a desired plasmid.
Question:
A genomic library is a collection of plasmids, each containing
different chromosomal fragments from the genome of an
organism. A cDNA library, on the other hand, contains only the
________ genome of an organism.
Answer:
coding sequences of genes
FEEDBACK: A cDNA library is a library of DNA fragments that are made from reverse
transcription of mRNA transcripts. This type of library contains only the coding sequences
of each gene, since introns are spliced out of mature mRNAs.
Question:
The first step of PCR requires that the DNA to be amplified is
Answer:
denatured.
FEEDBACK: In PCR, the target DNA must first be heated to denature the molecule into
single-stranded DNA. This allows the primers to bind in the second step by base-pairing
with their complementary sequence.
Question:
Approximately how many double-stranded DNA molecules
will be formed from one starting molecule after three rounds
of PCR?
Answer:
8
FEEDBACK: After the first cycle of a PCR reaction, each starting target DNA molecule
serves as the template for generating two new daughter molecules, comparable to DNA
,replication in cell. The second cycle will then duplicate each of the molecules from the
first cycle, producing four total molecules, and the third cycle duplicates each of those
four molecules into eight.
Question:
The DNA polymerase enzyme used in PCR is different from
the one used in human cells because it is able to
Answer:
withstand the high temperatures needed for denaturation.
FEEDBACK: PCR uses a polymerase that was isolated from a thermophilic bacterium. This
enzyme can withstand the high heat needed to denature the DNA strands in step one of
PCR.
Question:
The chain-termination method of sequencing relies on the
formation of partial copies of the DNA fragment that terminate
at each position in the sequence. The fragments are separated
by size and the terminating nucleotide is identified by
Answer:
the position in the capillary and a unique fluorescent tag on each nucleotide.
FEEDBACK: The chain-termination method of sequencing (or Sanger sequencing)
amplifies the DNA of interest to form many molecules that are randomly terminated by
the incorporation of one of four different fluorescently labeled dideoxynucleotides. The
fragments are separated by size in a capillary gel matrix and the fluorescent tags are
read to reveal the sequence of the DNA molecule.
Question:
The CRISPR system can be used to activate a gene by altering
the Cas9 enzyme in what way?
Answer:
fusing an inactive Cas9 to a transcriptional activator
FEEDBACK: Instead of targeting a Cas9 nuclease to a site for making a double-strand
break for genome editing, CRISPR can be used to target various activities to specific
, locations in the genome. This is done by inactivating the Cas9 so that it is no longer a
nuclease, and then attaching a protein with a desired activity.
Question:
Shown here is an expression vector. For the gene of interest to
be expressed in the cells, the gene of interest must be cloned
where in this vector?
Answer:
next to the promoter, in the proper orientation
FEEDBACK: Expression vectors contain a promoter that drives transcription of the gene
of interest. Promoters have directionality, so for the gene to be expressed, the gene must
be placed in the proper location relative to the promoter.
Question:
If a protein with a specific activity is isolated, how can the
encoding gene be identified?
Answer:
It can be identified by mass spectrometry followed by gene database searching.
FEEDBACK: Proteins of interest can be identified using mass spectrometry to determine
many short amino acid sequences read from the protein. These sequences can then be
compared to a database of all known protein-coding genes to identify the gene that
encodes this protein.
Question:
Gel electrophoresis separates DNA fragments from each
other by virtue of which feature?
Answer:
