Biology Class 12 NCERT Solutions: Chapter 11 Biotechnology: Principles and Processes Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q. 5 Do eukaryotic cells have restriction endonucleases? Justify your answer.


  • No, eukaryotic cells do not have restriction endonucleases. This is because the DNA of eukaryotes is highly methylated by a modified enzyme, called methylase.
  • Methylation protects the DNA from the activity of restriction enzymes.
  • These enzymes are present in prokaryotic cells where they help prevent the invasion of DNA by virus.
Restriction Enzyme

Q. 6 Besides better aeration and mixing properties what other advantages do stirred tank bioreactors have over shake flasks?


  • The shake flask method is used for a small-scale production of biotechnological products in a laboratory.
  • Whereas stirred tank bioreactors are used for a large-scale production of biotechnology products.
  • Stirred tank bioreactors have several advantages over shake flasks:

(i) Small volumes of culture can be taken out from the reactor for testing.

(ii) It has a foam breaker for regulating the foam.

(iii) It has a control system that regulates the temperature and .

Q. 7 Collect 5 examples of palindromic DNA sequences by consulting your teacher. Better try to create a palindromic sequence by following base-pair rules.


  • The palindromic sequence is a certain sequence of the DNA that reads the same whether read from 5՚ 3 ‘direction or from 3’ 5՚ direction.
  • They are the site for the action of restriction enzymes. Most restriction enzymes are palindromic sequences.
  • Five examples of palindromic sequences are-

(i) 5 ‘-AGCT-3’

3 ‘-TCGA-5’

(ii) 5 ‘-GAATTC-3’

3 ‘-CTTAAG-5’

(iii) 5 ‘-AAGCTT-3’

3 ‘-TTCGAA-5’

(iv) 5 ‘-GTCGAC-3’

3 ‘-CAGCTG-5’

(v) 5 ‘-CTGCAG-3’

3 ‘-GACGTC-5’

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