MCQs on Bacteriophage Lambda – 1
1 - Question
It is very important to study lambda biology as lambda phages are used for cloning purposes. Which of the statement is true for lambda phage?
a) It is an example of temperate phage
b) The fate of the phage is decided before it infects the cell
c) The lysis fate is that where the phage inserts its genome into the bacterial genome and the replication goes on
d) The lysogenic fate is that where the phage infects the cell and lysis is carried out
Explanation: Lambda phage is a temperate phage and its fate is decided as it infects the cell. It can be either be lytic or lysogenic in nature. Lytic phage is that which infects the cell and it is lysed whereas lysogenic phage is that in which phage genome is inserted into the bacterial genome and is replicated along with it.
2 - Question
Choose the correct statement for the infectious particle of lambda phage.
a) It is single stranded genome
b) It is circular double stranded genome
c) The ends are blunt with cos (cohesive) sequences
d) The ends are created by cleavage at cos sites during phage packaging
Explanation: The infectious particle of lambda phage id linear double stranded genome. The ends are staggered with cos (cohesive) sequences and they are created by cleavage at cos sites during phage packaging.
3 - Question
Some changes are encountered in the infectious particle as it infects the cell. Choose the incorrect statement.
a) The infectious particle circularizes upon causing infection by annealing at cos sites
b) There are two promoters present, PR and PL
c) Upon infection only PR is activated
d) Promoters give rise to immediate early transcripts
Explanation: As the infectious particle infects the cell it circularizes by annealing at cos sites. Both the promoters PR and PL are activated upon infection. Promoters give rise to immediate early transcripts which terminate at rightward and leftward terminators.
4 - Question
The immediate early transcripts direct synthesis of which genes?
a) N genes
b) cro genes
c) Both N and cro genes
d) PR and PL genes
Explanation: The immediate early transcripts are transcribed by promoters and they direct the synthesis of gene products of N and cro genes.
5 - Question
What is the function of the N gene?
a) It promotes the function of terminators
b) It overrides the function of terminators
c) It promotes the production of the cro gene
d) It is responsible for making the infectious particle linear
Explanation: N gene is responsible for overriding the function of terminators. As the terminators are overridden, the transcription is carried in the surrounding regions.
6 - Question
Choose the correct statement for cII gene and its related function?
a) The transcription is extended to the region of cII gene and it is termed as late transcription
b) They are responsible for deactivating the promoter for repressor establishment
c) This promoter is responsible to decide whether the life cycle would be lysogenic or lytic
d) cII gene is responsible for other gene which is gene cIII
Explanation: The cII gene product is formed when the transcription is extended because of the overriding of terminators by the N gene. It is responsible for activation of a promoter for repressor establishment. This promoter is responsible for deciding whether it would be in lysogenic or lytic mode. The transcripts formed by extension are called as delayed early transcripts and cIII is also produced along with cII.
7 - Question
Which gene is required for the lysogenic phage to be adopted?
d) All the three genes are interrelated
Explanation: All three genes are interrelated. The cII gene is protected from proteases by cIII gene and it further promotes the expression of cI gene. cI gene is necessary for silencing of rest of the lambda genome. cII is most important but as it related with other two as well, thus they all are required for lysogenic mode.
8 - Question
Choose the incorrect statement for lysogenic mode.
a) PRE forms cI gene product which is responsible for activation of promoters
b) The cII protein is responsible for interfering with cro and Q proteins and they are required for lytic life cycle
c) The cII protein activates the promoter PINT
d) The Int protein with host protein is responsible for site specific recombination
Explanation: The cI gene product is responsible for inactivation of promoters and thus silencing rest of the lambda genome. The cII gene product is responsible for interfering with cro and Q proteins and they are required for lytic life cycle. The cII gene also activates promoter PINT and the Int protein produced along with host protein is required for site specific recombination.
9 - Question
Choose the correct statement for the cI gene.
a) It represses only cII gene
b) It activates cII gene and represses cIII gene
c) It represses both cII and cIII gene
d) It activates both cII and cIII gene
Explanation: cI gene represses both cII and cIII gene and thus the expression of cIII is also suppressed.