Insertion of a foreign DNA at BamHI site in an E.coli cloning vector pBR322 results in the loss of antibiotic resistance towards:

Core Logic

Let's review the statements about restriction endonucleases:

• A is true: They are commonly known as molecular scissors.
• B is true: They form part of the defense mechanism in bacteria (like E. coli) to restrict bacteriophage growth by cutting viral DNA.
• C is false: They typically cut the DNA slightly away from the centre of the palindrome sites, but between the same two bases on the opposite strands, which creates sticky ends.
• D is false: Removing nucleotides from the ends of DNA is the function of restriction exonucleases, not endonucleases. Endonucleases cut at specific positions within the DNA.
• E is true: They do recognize specific palindromic nucleotide sequences.

Step 1: Final Conclusion

The statements that are NOT true are C and D.

Pattern Recognition

Endo = inside. Exo = outside (ends). Therefore, D is clearly false for an endonuclease. They create sticky ends by cutting off-center, making C false.

Chapter Mix

Class 12 Biology: Biotechnology Principles and Processes

Core Logic

• Genetically modified organism (A): Bt cotton is a famous transgenic (GMO) crop. (A-II)
• Thermostable DNA polymerase (B): Taq polymerase, used in PCR, is isolated from the hot spring bacterium Thermus aquaticus. (B-III)
• Ti plasmid (C): Tumor-inducing plasmid is extracted from the plant pathogen Agrobacterium tumefaciens. (C-I)
• pBR322 (D): The classic, artificially engineered plasmid vector used in Escherichia coli. (D-IV)

Step 1: Final Conclusion

The exact mapping is A-II, B-III, C-I, D-IV.

Pattern Recognition

Matching Taq (Thermostable) with Thermus aquaticus (B-III) and Ti Plasmid with Agrobacterium (C-I) are the most direct routes to the answer.

Chapter Mix

Class 12 Biology: Biotechnology Principles and Processes Class 12 Biology: Biotechnology and its Applications

Core Logic

A single cycle of Polymerase Chain Reaction (PCR) consists of three main steps:

• Denaturation: Heating the double-stranded DNA to separate the strands (around 94°C$94^{\circ}C$).
• Annealing: Cooling the reaction so that primers can bind (anneal) to their complementary sequences on the single-stranded template DNA.
• Extension: Taq polymerase synthesizes the new DNA strand by extending the primers.

Step 1: Final Conclusion

The correct sequence is Denaturation → Annealing → Extension.

Pattern Recognition

Acronym: DAE (Denaturation, Annealing, Extension).

Chapter Mix

Class 12 Biology: Biotechnology Principles and Processes

Core Logic

• Statement A is correct. DNA cutting is performed by restriction endonucleases, often referred to as molecular scissors.
• Statement B is correct. During gel electrophoresis, DNA fragments (which are negatively charged) move towards the anode and separate strictly according to their size due to the sieving effect of the agarose gel.
• Statement C is incorrect. Pure DNA fragments are invisible and cannot be seen under UV light without prior staining.
• Statement D is incorrect. Even when stained with ethidium bromide, DNA fragments are invisible in visible (normal) light; they only fluoresce bright orange when exposed to UV radiation.

Step 1: Final Conclusion

Only statements A and B are correct.

Pattern Recognition

Visualizing DNA requires BOTH staining (Ethidium bromide) AND UV light. Statements C and D break this rule by missing one of the prerequisites.

Chapter Mix

Class 12 Biology: Biotechnology Principles and Processes