Genetic Engineering Multiple Choice Questions on “Cloning in Lambda – 1”.
1. Insertion vectors are a type of vectors. Choose the correct statement for this type of vector.
a) These are complex vectors
b) DNA is inserted through many restriction sites
c) There is an upper limit on the size of the DNA to be packaged
d) Lambda gt09 is an example of this type of vector
Answer: c
Explanation: Insertion vectors are the simple vectors and DNA is inserted through a single restriction site. It must be a non-essential gene to maintain phage viability. There is an upper limit on the size of the DNA to be packaged thus only a few kilobases of the extra DNA can be included. Lambda gt10 and gt11 are an example of insertion vectors.
2. Choose the correct statement for lambda gt10.
a) It is having an EcoRI site
b) It is having cII gene
c) It accepts an insert of size greater than that of 8 kbp
d) This size is less than that the size which is generally accepted by wild type phage
Answer: a
Explanation: Lambda gt10 is having an EcoRI site which contains the cI repressor gene. It accepts an insert of size upto 7.6 kbp which is generally more than that of the size generally accepted by a wild type phage.
3. The presence of insert leads to inactivation of which gene?
a) cII
b) cI
c) cIII
d) both cII and cIII
Answer: b
Explanation: The presence of insert leads to inactivation of the cI gene and this is the method to detect the presence of an insert.
4. A portion of phage is removed and in place of it, the DNA of interest is inserted. This type of vector is called as __________
a) displacement vector
b) insertion vector
c) substitution vector
d) transposition vector
Answer: c
Explanation: If a portion of phage is removed and in its place, the DNA of interest is inserted, it is called as substitution or replacement vector.
5. Choose the incorrect statement for the central portion of the lambda genome.
a) The central portion is not required for lytic growth
b) The central portion includes repressor gene
c) The repressor gene is not required for lysogenic growth
d) It is approximately 10kbp long
Answer: d
Explanation: The central portion of the lambda genome is approximately 20 kbp and it is not required for lytic growth. The central portion constitutes of repressor gene and thus it has to be removed for the lysogenic growth to take place.
6. The fragment inserted in the place of the central portion of the genome is known as __________
a) insertion fragment
b) substitution fragment
c) stuffer fragment
d) displacement fragment
Answer: c
Explanation: The fragment inserted in the place of the central portion of the genome is known as the stuffer fragment. It is generated by doing partial digestion an enzyme having a 4bp long recognition site.
7. Choose incorrect statement for the substitution vector EMBL4.
a) It is having two single multiple cloning sites
b) The region to be removed is on one side of the multiple cloning sites
c) If a digestion within the multiple cloning sites, it generates central portion and right and left arms
d) The right and left portions are called as arms
Answer: b
Explanation: The substitution vector EMBL4 contains two multiple cloning sites. The two multiple cloning sites flank the region which is to be removed. If digestion is done within the multiple cloning sites, it generates central portion and the right and left portions. The right and left portions separated are known as arms.
8. Is it necessary to stop the relegation of the central portion before the stiffer fragment is ligated.
a) True
b) False
Answer: a
Explanation: The central portion should be stopped from religating before the stuffer fragment should be ligated. There are chances that central portion gets religated to the arms.
9. At times, a second enzyme is used while the central portion is removed and the stuffer fragment is placed there. Choose the statement which doesn’t holds for this process.
a) It is a method which is used for avoiding the relegation of central portion before the stuffer fragment is attached over there
b) In this method, the central portion is cut with another enzyme after being separated from the arms
c) The arms are also cut with this second enzyme
d) It is not necessary to remove the fragments generated
Answer: c
Explanation: A second enzyme is used in order to avoid the relegation of the central portion and the arms. In this method, the central portion is cut with a second enzyme after being separated from the arms. These arms are not cut with the second enzymes. Hence the ends created are different now and the arms won’t ligate to the central portion again. It is not necessary to remove the fragments generated because the chances of having a multimolecular reaction which are required for the formation of original phage are very less.
10. Physical separation is also used at times. Choose the correct statement with respect to this method.
a) Physical separation constitutes of gel electrophoresis and or by using centrifugation in sugar density gradient
b) In sugar density gradient, the molecules are separated on the basis of density
c) The central portion is recovered from the gel or the gradient
d) Gel is more efficient than the sugar density gradient
Answer: a
Explanation: Physical separation is also used at times, it constitutes of using gel electrophoresis or by using centrifugation in the sugar density gradient. In the sugar density gradient, the separation is done on the basis of size. The arms are separated from the gel or gradient. A gradient is more efficient than gel, thus gradient is more preferred over the gel.
11. Packaging in vitro is also carried out to introduce the lambda DNA into the cells. Choose the incorrect statement in respect to it.
a) Packaging in phage coat is a more efficient process than the normal transformation process
b) The lambda DNA is incubated with lysate of lambda infected cells in a concatemeric configuration
c) Lysate constitutes of lambda proteins needed for phage assembly
d) The amount of non-recombinant phage in the background is less
Answer: d
Explanation: Packaging in vitro is used to introduce the lambda. It is more efficient than the normal transformation procedure. Thus, the lambda DNA is incubated with lysate of lambda infected cells in a concatemeric configuration. This lysate constitutes of lambda proteins needed for phage assembly and hence the recombinant DNA is also packed. But there is also a large amount of non-recombinant packaging in the background.
12. Packaging in vitro is basically carried out by two different strategies. Choose the incorrect statement for it.
a) Separate strains with chain-termination mutations in different genes for coat components are used __________
b) Temperature sensitive cI repressor is used
c) Due to heat shock packaging proteins are induced
d) Packaging is carried out in each strain
Answer: d
Explanation: Packaging in vitro is basically out by two different strategies. In the first strategy, separate strains with chain-termination mutations in different genes (mostly D and E genes) for coat components are used. Temperature sensitive cI repressor is used and due to induction by heat shock, packaging proteins are produced. But packaging is not carried out in any of the strain because none of the strain is having full complement of proteins to carry out packaging.
13. Chain-termination mutations in coat proteins genes are carried out. The coat protein coat genes used are __________
a) A gene
b) D gene
c) E and D gene
d) D and A gene
Answer: c
Explanation: Chain-termination mutations in coat proteins genes are carried out, these genes are D and E genes.