Question

Question 5 (1 point) What is the order of events in infection by lambda phage? | The phage P(R) and P(L) promoters are switched on Either the phage becomes lysogenic or lytic. > The phage enters E. coli > Either the phage P(RM) or P(RE) promoter is switched on. > cro and c(l) complete for the O(R1), O(R2), and O(R3) operators. Question 6 (1 point) (Multiselect) For phage lambda to enter the lysogenic cycle: cro must occupy the R1 operator. cro must occupy the R2 operator. cro must occupy the R3 operator. cl must occupy the R1 operator. cl must occupy the R2 operator. Ocl must occupy the R3 operator. Question 7 (1 point) In eukaryotes, transcriptional gene control is mediated by Otrans-acting factors binding to cis-acting elements. trans-acting factors failing to bind to cis-acting elements. O repressor proteins binding to operator sites. O metabolites binding to cis-acting elements. Onone of the above.

Answer 1

Q.5. The order of event is given as follows

• The phage enter E-coli
• either the phage becomes lysogenic or lytic
• The P(R) and P(L) promoters are switched on
• Either the phage P(RM) or P(ER) is switched on
• cro and c(l) complete for O(R1), O(R2) and O(R3) operators

Q.6. Option 4 and 5 i.e. cl must occupy R1 operator and cl must occupy R2 operator

The life cycle of lambda phages is controlled by cI and Cro proteins. The lambda phage will remain in the lysogenic state if cI proteins predominate, but will be transformed into the lytic cycle if cro proteins predominate. cI is responsible for maintaining the lysogenic life cycle of phage Lambda. If cI binds to OR1 or OR2 then PRM is activated which further has significance in lysogenic cycle. when cI binds to OR3 the PRM  is blocked.

cro gene control the lytic cycle.

Q.7. Option 1 i.e. trans-acting elements binding to cis acting element

A trans-acting factor is usually a regulatory protein that binds to DNA. The binding of a trans-acting factor to a cis-regulatory element in DNA can cause changes in transcriptional expression levels.

If trans-acting factors fails to bind cis-acting elements then it does not support transcription process

A repressor is a DNA- or RNA-binding protein that inhibits the expression of one or more genes by binding to the operator or associated silencers. A DNA-binding repressor blocks the attachment of RNA polymerase to the promoter, thus preventing transcription of the genes into messenger RNA.

When metabolites binds cis acting elements they regulate the occlusion of signals for transcription process to reduce or translation initiation