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Biotechnology - Principles and Processes class 12 Notes Biology. (CBSE) Very helpful to revise the whole syllabus during exam days. (PDF in Question - Answer format)
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Biotechnology - Principles and Processes1. Describe the mechanism of action of restriction exonuclease.
Answer:
• Every restriction endonuclease functions by inspecting the length of a particular DNA
sequence.
• Once it recognises a specific recognition sequence, it binds to DNA.
• It cuts each of the two strands of double helix at specific points in their sugar phosphate
backbone.
• Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome
sites, but between the same two bases on the opposite strands. This leaves single stranded
portions at the ends and the overhanging stretches are called sticky ends on each strand.
• Each restriction endonuclease recognises a specific palindromic nucleotide sequence in the
DNA.
• When cut by the same restriction enzyme, the resultant DNA fragments have the same kind
of ‘sticky-ends’ and, these can be joined together using DNA ligases.
2. What is a palindrome in DNA?
Answer: The palindrome in DNA is a sequence of base pairs that reads same on the two strands
when orientation of reading is kept the same.
For example, the following sequences reads the same on the two strands in 5' to 3' direction and
3' to 5' direction.
5' – GAATTC – 3'
3' – CTTAAG – 5'
3. What are sticky ends? Why are they named so?
Answer: The single stranded overhanging stretches on each strand of DNA after being cut by
the restriction enzymes are called sticky ends. These are named so because they form hydrogen
bonds with their complementary cut counterparts. This stickiness of the ends facilitates the
action of the enzyme DNA ligase.
4. What are the two types of nucleases? What are their functions?
Answer:
Nucleases are of two kinds –
• Exonucleases: Remove nucleotides from the ends of the DNA.
• Endonucleases: They make cuts at specific positions within the DNA.
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