MCQs on Gel electrophoresis, Oligonucleotide & Microarrays – 3
1 - Question
Often the DNA or RNA needs to be removed from the gel to the solid support. The process can be termed as ____________
d) DNA purification
Explanation: At times, the DNA or RNA needs to be transferred from the gel to the solid support for various purposes such as analyses. This process is termed as blotting.
2 - Question
Which of the following steps is not included in the transferring of DNA?
a) The gel containing the DNA is immersed in the buffer in the reservoir
b) The buffer flows up through the gel via a wick
c) Membrane is placed over the gel
d) The nucleic acids are dissolved in the buffer and are obtained from it via pipetting
Explanation: The gel containing the DNA molecules is immersed in the buffer. The membrane is placed over the gel. The buffer rises from the wick and passes through the gel. It carries along with it, the nucleic acids and they are then trapped by the membrane. The membrane can be washed further in order to obtain the DNA.
3 - Question
If the DNA samples are to be analyzed, the membrane should be studied. Which of them is correct for it?
a) The membrane should not be treated with UV or heat
b) The membrane is further immersed in the buffer containing labelled nucleic acids which are known as strips
c) Labelled nucleic acids bind to the sequences which are same as the sequences present on the membrane
d) The binded sequences can be visualized by autoradiography
Explanation: The membrane should be treated with UV or heated. It ensures the cross linking of the DNA molecules on the membrane. The labelled nuclei in the buffer are called a probe. These sequences bind to the complementary sequences on the membrane and can be visualized via autoradiography.
4 - Question
In the case DNA is transferred from gel to the membrane, it is known as ____________
a) southern blot
b) western blot
c) northern blot
d) south-western blot
Explanation: For the DNA to be transferred, it is called a southern blot. If RNA is to be transferred it is called as northern blot. For transferring of proteins it is called a western blot.
5 - Question
Oligonucleotides can’t be referred to ____________
a) undefined sequences
b) sequences that can be used as PCR primers
c) sequences that can be used in DNA sequencing
d) sequences that can be used in identifying complementary DNA molecules
Explanation: Oligonucleotide is the defined sequences which are having various purposes such as primers in PCR. They are also used in DNA sequencing. Oligonucleotides can be used as probes in complementary base pairing reactions.
6 - Question
Oligonucleotides are synthesized chemically. Which of the following step is involved in oligonucleotide synthesis?
a) Nucleotide addition is done by adding many nucleotides at a time
b) The coupling reaction should involve water
c) Only one type of nucleotides can be added at a time
d) Unblocking of the reactive groups leads to addition of nucleotides
Explanation: Oligonucleotide synthesis is done on the basis of blocking the reactive groups so that only one nucleotide is added as the unblocking is done. The coupling reaction should not involve water because than water will do nucleophilic reaction. A mixture of nucleotides can be added at a time.
7 - Question
If the known DNA sequences are immobilized onto a solid support, it is called ____________
c) DNA plate
Explanation: In the case known DNA sequences are immobilized on a solid support, the arrangement is called a microarray. If unknown sequences are immobilized, it is called a blot.
8 - Question
In the case of microarrays ____________
a) Often the whole organism is not sequenced
b) Changes in transcript level can be studied in response to environmental changes
c) RNA is synthesized only after the property which is to be studied is inculcated
d) DNA is synthesized for this RNA by transcriptase
Explanation: In microarrays, often the whole organism is sequenced on the solid support such as a slide. The change in the transcript level can be studied in response to environmental changes. The RNA is synthesized both for before and after the change is to be studied. DNA is synthesized for both RNAs by reverse transcriptase.
9 - Question
The DNA is labelled with fluorescent dyes in order to study the level of transcription.
Explanation: The DNA is labelled with fluorescent dyes. The amount of fluorescence they give corresponds to the level of transcription. The dyes which are often used are Cy3 and Cy5.
10 - Question
If undefined sequences are immobilized, the set up is called ____________
d) DNA chip
Explanation: In the case, undefined sequences are immobilized; the set up is called a DNA chip. They can be used by synthesis of oligonucleotides in situ using photolithography technology from the microelectronics industry.