Question

Q4 The 4.2-kb plasmid pMR102 has genes for resistance to the antibiotics ampicillin (ApR) and tetracycline (TcR). The plasmid has several restriction sites that can be used for DNA cloning. The PstI site lies in the middle of the TcR while the BamHI site is in the middle of the ApR in pMR102. A plant gene cut by BamHI was ligated with BamHI cut pMR102 DNA. The ligated mixture was transformed into E. coli, and the transformants were selected on LB growth medium containing tetracycline (LB + Tc). The transformants were then replica plated onto LB + Ap (LB growth medium containing ampicillin) and LB + Tc plates as shown in the figure. After 24 hrs incubation at 37 OC, plates were observed for growth. All transformants showed growth on LB + Tc plate but not on LB + Ap plate.

Identify the statements as True or False

A. Cells with plasmids containing the disrupted ApR gene will not grow on LB + Ap plate.

B. Cells containing the recombinant plasmids will grow on both plates.

C. A colony growing on LB + Ap will have only those cells that contain re-circularized plasmids.

D. Cells growing at position 7 on both plates will have a recombinant plasmid.

E. Cells growing at position 7 on both plate will have a re-circularized plasmid.

F. Cells growing at position 7 on both plate may have a re-circularized or recombinant plasmid.

G. Cells growing at position 1 only on LB +Tc plate will have a re-circularized plasmid.

H. Cells growing at position 1 only on LB +Tc plate will have a recombinant plasmid.

I. Cells growing at position 1 only on LB +Tc plate may have a re-circularized or recombinant plasmid.

Answer 1

Figure is not provided (insufficient information) in the question but statement clearly says that transformants did not grow on LB + Ap plate. So this question can be answered without the figure also. This is the reason I am answering this question.

Answer:

following statements are correct for the above given situation (transformants showed growth only on LB + Tc plate but not on LB + Ap plate).

True statements: (A) and (H) are true for the given situation.

A. Cells with plasmids containing the disrupted ApR gene will not grow on LB + Ap plate (true, because ApR will not be functional).

H. Cells growing at position 1 only on LB +Tc plate will have a recombinant plasmid (true, because it is growing only on LB + Tc plate not on LB + Ap plate).

False statements: (B, C, D, E, F, G and I) are false for the given situation.

B. Cells containing the recombinant plasmids will grow on both plates (False, because it contains the disrupted ApR gene that will not be functional. Recombinant plasmids will not grow on LB + Ap plate).

C. A colony growing on LB + Ap will have only those cells that contain re-circularized plasmids (false for the given situation, because there is no colony on LB + Ap plate) .

D. Cells growing at position 7 on both plates will have a recombinant plasmid (False, because it contains the disrupted ApR gene that will not be functional. Recombinant plasmids will not grow on LB + Ap plate).

E. Cells growing at position 7 on both plate will have a re-circularized plasmid. (if this statement is correct than next statement (F) will not be correct, because only re-circularized plasmid or self-ligated plasmids can grow on LB + Ap plate not the recombinant plasmid. LB +Tc plate may have a re-circularized or recombinant plasmid).

F. Cells growing at position 7 on both plate may have a re-circularized or recombinant plasmid (see the explanation in statement E).

G. Cells growing at position 1 only on LB +Tc plate will have a re-circularized plasmid (False, because if it is re-circularized plasmid it should grow on both the plate not only on LB +Tc plate. See the explanation in statement E).

I. Cells growing at position 1 only on LB +Tc plate may have a re-circularized or recombinant plasmid (false, because it is only growing on LB + Tc plate not on LB + Ap plate).

But few statements can be true, if few colonies (especially colony 1 and 7) will grow on the both the LB +Tc plate as well as on LB + Ap plate.

C. A colony growing on LB + Ap will have only those cells that contain re-circularized plasmids.

E. Cells growing at position 7 on both plate will have a re-circularized plasmid. (if this statement is correct than next statement (F) will not be correct, because only re-circularized plasmid or self-ligated plasmids can grow on LB + Ap plate not the recombinant plasmid. LB +Tc plate may have a re-circularized or recombinant plasmid).

F. Cells growing at position 7 on both plate may have a re-circularized or recombinant plasmid (see the explanation in statement E).

G. Cells growing at position 1 only on LB +Tc plate will have a re-circularized plasmid (False, because if it is re-circularized plasmid it should grow on both the plate not only on LB +Tc plate.  See the explanation in statement E).

I. Cells growing at position 1 only on LB +Tc plate may have a re-circularized or recombinant plasmid (false, because it is only growing on LB + Tc plate not on LB + Ap plate).