Question

Given below are two statements.
Statement I: Restriction enzyme BamHI has its recognition site in tet$^{R}$ region of pBR322.
Statement II: E.coli having pBR322 with a desired DNA if inserted at BamHI site can grow in medium containing tetracycline.
In the light of the above statements, choose the correct answer from the options given below.

• A. Both Statement I and Statement II are true
• B. Both Statement I and Statement II are false
• C. Statement I is true, but Statement II is false
• D. Statement I is false, but Statement II is true

Hint:

Insertional inactivation means putting a gene inside a resistance gene destroys that resistance. Insertion in BamHI $\rightarrow$ loss of Tetracycline resistance.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept: The plasmid pBR322 is a widely used cloning vector that contains specific antibiotic resistance genes with designated restriction sites.
Step 2: Key Formula or Approach: Recall the map of pBR322 and apply the concept of insertional inactivation to determine the survival of recombinant bacteria.
Step 3: Detailed Explanation: Statement I states that BamHI has its recognition site in the tetracycline resistance (tet$^{R}$) region of pBR322.
This is factually true; both BamHI and SalI are located within the tet$^{R}$ gene.
Statement II claims that E.coli having pBR322 with a desired DNA inserted at the BamHI site can still grow in a medium containing tetracycline.
This is false due to "insertional inactivation."
When foreign DNA is inserted at the BamHI site, the tet$^{R}$ gene gets disrupted and loses its function.
Consequently, the recombinant E.coli will lose resistance to tetracycline and will not be able to grow in a tetracycline-containing medium.
Step 4: Final Answer: Statement I is true, and Statement II is false.