MCQs on Cloning the cDNA and Specialized Libraries – 2
1 - Question
Sometimes the required mRNA is present in less number. So the process of increasing the representation of rare mRNAs is called as ____________
Explanation: If the required mRNA is present in less number, its representation can be increased by a process called normalization. It reduces the number of times the library has to be screened for required cDNA.
2 - Question
Choose the correct statement in order to enrich rare species.
a) The most basic principle relies on the kinetics of hybridization
b) A collection of single stranded molecules is allowed to reanneal under given conditions
c) The strands which are less abundant are able to find their complement easily
d) The left over molecules are more abundant in nature
Explanation: In order to enrich the rare species, the basic principle relies on the kinetics of hybridisation. A collection of double stranded cDNA molecules is allowed to melt. As the strands melt away, they are then allowed to reanneal under suitable conditions. The more abundant the species is, the more easily they anneal. The rare species are obtained in single stranded form because it is difficult to reanneal them.
3 - Question
Which statement holds true for hydroxyapatite?
a) It binds to single stranded molecules more tightly than double stranded molecules
b) It binds to linear molecules more tightly than circular molecules
c) It binds to circular molecules more tightly than linear molecules
d) It binds to double stranded molecules more tightly than single stranded molecules
Explanation: Hydroxyapatite is the molecule which binds more tightly to the double stranded molecules than the single stranded molecules. This property is very useful in the process of enrichment of rare species.
4 - Question
Libraries in which a particular sequence is present in one organism but are absent from another organism, are called as ___________
a) normalized libraries
b) subtractive libraries
c) selective libraries
d) partial libraries
Explanation: Sometimes it happens that a particular sequence is present in one organism but is absent from another organism, such libraries are known as subtractive libraries.
5 - Question
The nucleic acid from the cell type that contains the sequence we are interested in is called ___________
b) subtractive sequence
d) wanted sequence
Explanation: The nucleic acid from the cell type containing the sequence we are interested in is called a tracer. The driver is the molecule which lacks the sequence.
6 - Question
Choose the correct statement for libraries constructed by mixing cell types differing in the sequences they are having.
a) The driver and tracer are mixed in double stranded form
b) Tracer is in stoichiometric excess in comparison to driver
c) Tracer and driver are in the same amount
d) The sequences are allowed to hybridize
Explanation: It is about subtractive libraries. The driver and tracer are mixed in single stranded form and driver is in stoichiometric excess in comparison to the driver. It is about tenfold excess. The sequences are mixed and allowed to hybridize.
7 - Question
Which of the following is desirable?
a) Driver- driver hybrid
b) Driver- tracer hybrid
c) Tracer- tracer hybrid
d) Driver alone
Explanation: Our sequence of interest is present in the tracer. So if it hybridizes with a driver, it means that the sequence is present is it also and thus it is not required by us. Hence, either tracer-tracer hybrids or single stranded tracers are required.
8 - Question
Which of the statement holds true?
a) The tracer is treated with an enzyme which generates compatible ends
b) The driver is treated with an enzyme which generates compatible ends
c) Both driver and tracer are treated with an enzyme to generate compatible ends
d) Both driver and tracer are treated with an enzyme to generate incompatible ends
Explanation: The tracer is treated with an enzyme which generates compatible ends and the driver is treated to generate incompatible ends. It is done so because then driver-driver or driver-tracer hybrids won’t form. Only tracer-tracer hybrids would form.
9 - Question
If physical methods are used, tracer is amplified and is labelled with biotin.
Explanation: In the case of physical removal methods, the driver is amplified and is labelled with biotin. After hybridization between tracer and driver, streptavidin is added and it attaches to biotin. Methods such as phenol extraction are used in order to remove streptavidin and sequences attached to it. Thus, tracer sequences which are not attached to driver remain in the aqueous phase only.
10 - Question
Sometimes a gene which we want to clone is present on a particular chromosome. For this purpose, the chromosome should be in which phase?
Explanation: The chromosomes should be in metaphase state because then they will be in a condensed form and it would be easy to handle them.
11 - Question
For cloning purposes, the intact chromosomes should be separated by ___________
a) agarose gel electrophoresis
b) fluorescence- activated sorter
c) polyacrylamide gel electrophoresis
Explanation: For cloning purposes, the intact chromosomes should be separated by using fluorescence-activated sorter. The amount of fluorescence obtained is based on the amount of dye and thus depends on the size of the chromosome.
12 - Question
The process of examining stained chromosomes in a light microscope and removing appropriate regions with a micro-manipulator is called as ___________
b) chromosome sorting
c) chromosome walking
d) chromosome jumping
Explanation: The process of separating the region of interest from a chromosome is termed as microdissection. It is carried out by firstly staining the chromosome and then observing it under a light microscope.