Plasmid pBR322 has PstI restriction enzyme site
within gene ampR that confers ampicillin resistance. If this enzyme is used for inserting a gene for β-galactoside production and the recombinant plasmid is inserted in an E.coli strain
Explanation:
In pBR322, the ampR gene provides ampicillin resistance. If PstI cuts within ampR to insert a β-galactoside gene, ampR is disrupted, so the plasmid can no longer confer ampicillin resistance. Therefore, transformed E. coli would not survive ampicillin unless ampR remains functional. Hence, option 1 is correct. Options 2 and 4 assume both resistance and new function, which is unlikely when ampR is inactivated by insertion. Option 3 about lysis is not a general consequence of such recombination.
🧠 Did You Know?
In blue-white screening, insertion of a foreign gene into lacZ (β-galactosidase gene) often disrupts beta-galactosidase production, helping identify recombinant colonies.
💡 NCERT Memory Line:
Restriction enzymes create cuts at specific sites; inserting foreign DNA into a plasmid can disrupt a gene (e.g., ampR) and alter antibiotic resistance.
During the process of gene amplification using PCR, if very high temperature is not maintained in the beginning, then which of the following steps of PCR will be affected first?
Option 3 is correct. Restriction enzyme digestions involve incubating purified DNA with restriction enzymes under optimum conditions to cut DNA at specific sequences. This is a standard step in gene cloning as per NCERT.
🧠 Did You Know?
Gel electrophoresis (option 1) is for separating DNA fragments, not amplifying them. PCR (option 4) amplifies DNA, not isolates or separates it. Ligation by DNA ligase (not listed) joins gene and vector (a different process from what PCR or restriction digestion does).
💡 NCERT Memory Line:
Restriction enzymes cut DNA at specific sites; PCR amplifies target DNA segments; gel electrophoresis separates DNA fragments by size.
In Recombinant DNA technology antibiotics are used:
Explanation:
In recombinant DNA technology, antibiotics are used as selectable markers. Bacteria that have taken up the recombinant plasmid usually carry an antibiotic resistance gene. When grown on a medium containing the antibiotic, only those cells with the plasmid survive, enabling easy identification of successful transformants.
🧠 Did You Know?
Selectable markers help distinguish cells that have incorporated the desired DNA from those that have not.
💡 NCERT Memory Line:
Antibiotics in the culture medium select only the transformed cells that contain the marker gene.
