Endonucleases function by making cuts at:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Random positions within the DNA
• The ends of the DNA
• Specific positions within the DNA
• Only blunt ends
Correct Option: C  [ Specific positions within the DNA ]

Remark: Endonucleases make cuts at specific positions within the DNA.

A restriction endonuclease cuts the DNA double helix at specific points in which part of the strands?

[Biotechnology-Principles-and-Processes] [class-xii ]

• Nitrogenous base links
• Hydrogen bonds
• Sugar-phosphate backbones
• Carbon chain
Correct Option: C  [ Sugar-phosphate backbones ]

Remark: Restriction endonucleases cut each of the two strands of the double helix at specific points in their sugar-phosphate backbones.

Each restriction endonuclease recognizes a specific kind of nucleotide sequence known as a:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Repetitive sequence
• Palindromic sequence
• Random sequence
• Non-coding sequence
Correct Option: B  [ Palindromic sequence ]

Remark: Each restriction endonuclease recognises a specific palindromic nucleotide sequence in the DNA.

Restriction enzymes cut the DNA strands away from the center of the palindrome site, leaving overhanging stretches called:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Blunt ends
• Sticky ends
• Recognition loops
• Restriction loops
Correct Option: B  [ Sticky ends ]

Remark: The overhanging stretches are called sticky ends, facilitating joining.

Sticky ends facilitate the action of DNA ligase by forming which type of bonds with their complementary cut counterparts?

[Biotechnology-Principles-and-Processes] [class-xii ]

• Covalent bonds
• Ionic bonds
• Hydrogen bonds
• Peptide bonds
Correct Option: C  [ Hydrogen bonds ]

Remark: Sticky ends form hydrogen bonds with their complementary cut counterparts, which facilitates the action of DNA ligase.

Recombinant DNA molecules are composed of DNA derived from:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Identical sources/genomes
• Parental sources only
• Different sources/genomes
• Single prokaryotic sources
Correct Option: C  [ Different sources/genomes ]

Remark: Restriction endonucleases are used to form ‘recombinant’ molecules of DNA, which are composed of DNA from different sources/genomes.

The technique used to separate DNA fragments resulting from restriction endonuclease digestion is known as:

[Biotechnology-Principles-and-Processes] [class-xii ]

• PCR
• Gel electrophoresis
• Transformation
• Downstream processing
Correct Option: B  [ Gel electrophoresis ]

Remark: The fragments of DNA can be separated by a technique known as gel electrophoresis.

DNA fragments move towards the anode during gel electrophoresis because:

[Biotechnology-Principles-and-Processes] [class-xii ]

• They are positively charged
• They are negatively charged
• They are neutral molecules
• The medium attracts them randomly
Correct Option: B  [ They are negatively charged ]

Remark: Since DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode.

The most commonly used matrix for separating DNA fragments in gel electrophoresis is agarose, which is extracted from:

[Biotechnology-Principles-and-Processes] [class-xii ]

• Fungi
• Bacteria
• Sea weeds
• Plant roots
Correct Option: C  [ Sea weeds ]

Remark: Agarose is a natural polymer extracted from sea weeds.

In gel electrophoresis, how do DNA fragments separate based on size?

[Biotechnology-Principles-and-Processes] [class-xii ]

• Larger fragments move farther
• Smaller fragments move farther
• Fragments move independent of size
• All fragments move the same distance
Correct Option: B  [ Smaller fragments move farther ]

Remark: The smaller the fragment size, the farther it moves, due to the sieving effect provided by the agarose gel.