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Q12(c):
Discuss with your teacher and find out how to distinguish between (c) Exonuclease and Endonuclease
Solution :
1. Theoretical Foundation: Nucleases
Nucleases are enzymes capable of cleaving the phosphodiester bonds between nucleotide subunits of nucleic acids. The distinction between Exonucleases and Endonucleases is categorized by their specific site of action within the polynucleotide chain [Per the biochemical classification of restriction enzymes].
2. Comparative Analytical Framework
| Feature | Exonuclease | Endonuclease |
|---|---|---|
| Cleavage Site | Acts only at the ends ($5'$ or $3'$) of the DNA molecule. | Acts at specific internal sites within the DNA molecule. |
| Mechanism | Removes nucleotides one by one from the terminal ends. | Breaks internal phosphodiester bonds, creating DNA fragments. |
| Biological Role | DNA proofreading, repair, and degradation of linear DNA. | Restriction modification systems, defense against viral DNA. |
| Product | Produces individual mononucleotides. | Produces polynucleotide fragments (sticky or blunt ends). |
3. Step-by-Step Distinguishing Logic
Step 1: Analyzing Positional Specificity
Exonucleases require a free $3'$-OH or $5'$-phosphate terminus to initiate catalysis. If a DNA molecule is circularized (e.g., in many prokaryotic plasmids), exonucleases are rendered inactive unless a nick is introduced [By structural constraint].
Step 2: Analyzing Sequence Recognition
Endonucleases, particularly Type II Restriction Endonucleases used in recombinant DNA technology, recognize specific palindromic sequences (e.g., GAATTC for EcoRI). Exonucleases generally lack sequence specificity and operate based on the accessibility of the termini.
Step 3: Evaluating Recombinant Application
In biotechnology, endonucleases are prioritized for gene cloning because they cut DNA into predictable, manageable fragments. Exonucleases are utilized primarily in enzymatic labeling or DNA degradation protocols where sequence preservation is not the objective.
Final Solution: Exonucleases cleave nucleotides specifically from the terminal ends of a DNA molecule, whereas endonucleases catalyze the hydrolysis of internal phosphodiester bonds at specific recognition sequences, making them essential tools for molecular cloning.
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(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
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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