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Q11(b):
Explain briefly
(b) Restriction enzymes and DNA
Solution :
1. Conceptual Foundation: The Biological Scissors
Restriction enzymes, specifically Restriction Endonucleases, are proteins synthesized by bacteria as a defense mechanism against bacteriophage infections [Per the Restriction-Modification System theory]. These enzymes catalyze the hydrolysis of phosphodiester bonds at specific nucleotide sequences known as recognition sites or palindromic sequences.
2. Classification and Mechanism of Action
Restriction enzymes are categorized primarily into Type I, II, and III. In biotechnology, Type II enzymes are utilized because they recognize specific palindromic sequences and cut the DNA molecule within or near that site without requiring ATP hydrolysis [Ref: Molecular Biology of the Gene].
| Feature | Mechanism |
|---|---|
| Recognition Sequence | Specific 4-8 bp palindromic sequence (e.g., GAATTC for EcoRI). |
| Cleavage Type | Produces either "sticky ends" (staggered cuts) or "blunt ends" (even cuts). |
3. Interaction with DNA
The interaction follows a precise biochemical pathway:
- Scanning: The enzyme binds to the DNA backbone and slides along the molecule [By the theory of facilitated diffusion].
- Recognition: The enzyme identifies the specific inverted repeat sequence.
- Cleavage: Upon binding, a conformational change occurs, allowing the enzyme to catalyze the nucleophilic attack on the phosphodiester bond.
4. Visual Representation: Palindromic Cleavage
5. Analytical Significance in Recombinant DNA Technology
The ability of restriction enzymes to generate sticky ends is vital for the creation of Recombinant DNA. Because these staggered cuts result in single-stranded overhanging protrusions, they can form hydrogen bonds with complementary sequences on a vector (e.g., a plasmid) via base pairing [Per Watson-Crick pairing rules]. Subsequently, the enzyme DNA Ligase is utilized to covalently seal the phosphodiester backbone, creating a stable recombinant molecule.
Final Solution: Restriction enzymes are site-specific endonucleases that recognize palindromic sequences in DNA. By cleaving the phosphodiester bonds at these locations, they create specific DNA fragments (often with cohesive sticky ends) that act as the fundamental building blocks for gene cloning and the assembly of recombinant DNA molecules.
More Questions from Class 12 Biology Biotechnology: Principles and Processes EXERCISES
- Q1: Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics (use the internet).
- Q1: Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics (use the internet).
- Q2: Make a chart (with diagrammatic representation) showing a restriction enzyme, the substrate DNA on which it acts, the site at which it cuts DNA and the product it produces.
- Q2: Make a chart (with diagrammatic representation) showing a restriction enzyme, the substrate DNA on which it acts, the site at which it cuts DNA and the product it produces.
- Q3: From what you have learnt, can you tell whether enzymes are bigger or DNA is bigger in molecular size? How did you know?
- Q3: From what you have learnt, can you tell whether enzymes are bigger or DNA is bigger in molecular size? How did you know?
- Q4: What would be the molar concentration of human DNA in a human cell? Consult your teacher.
- Q4: What would be the molar concentration of human DNA in a human cell? Consult your teacher.
- Q5: Do eukaryotic cells have restriction endonucleases? Justify your answer.
- Q5: Do eukaryotic cells have restriction endonucleases? Justify your answer.
- Q6: Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?
- Q6: Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?
- Q7: Collect 5 examples of palindromic DNA sequences by consulting your teacher. Better try to create a palindromic sequence by following base-pair rules.
- Q7: Collect 5 examples of palindromic DNA sequences by consulting your teacher. Better try to create a palindromic sequence by following base-pair rules.
- Q8: Can you recall meiosis and indicate at what stage a recombinant DNA is made?
- Q8: Can you recall meiosis and indicate at what stage a recombinant DNA is made?
- Q9: Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?
- Q9: Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?
- Q10(a): Describe briefly the following: (a) Origin of replication
- Q10(a): Describe briefly the following: (a) Origin of replication
- Q10(b): Describe briefly the following: (b) Bioreactors
- Q10(b): Describe briefly the following: (b) Bioreactors
- Q10(c): Describe briefly the following: (c) Downstream processing
- Q10(c): Describe briefly the following: (c) Downstream processing
- Q11(a): Explain briefly (a) PCR
- Q11(a): Explain briefly (a) PCR
- Q11(b): Explain briefly (b) Restriction enzymes and DNA
- Q11(c): Explain briefly (c) Chitinase
- Q11(c): Explain briefly (c) Chitinase
- Q12(a): Discuss with your teacher and find out how to distinguish between (a) Plasmid DNA and Chromosomal DNA
- Q12(a): Discuss with your teacher and find out how to distinguish between (a) Plasmid DNA and Chromosomal DNA
- Q12(b): Discuss with your teacher and find out how to distinguish between (b) RNA and DNA
- Q12(b): Discuss with your teacher and find out how to distinguish between (b) RNA and DNA
- Q12(c): Discuss with your teacher and find out how to distinguish between (c) Exonuclease and Endonuclease
- Q12(c): Discuss with your teacher and find out how to distinguish between (c) Exonuclease and Endonuclease
CBSE Solutions for Class 12 Biology Biotechnology: Principles and Processes
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Human Health and Disease
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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