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Q12(c):
Discuss with your teacher and find out how to distinguish between
(c) Exonuclease and Endonuclease
Solution :
1. Definitions and Molecular Mechanisms
Nucleases are enzymes that catalyze the hydrolysis of phosphodiester bonds within nucleic acid molecules. The distinction between Exonucleases and Endonucleases is based specifically on their site of action relative to the termini of the polynucleotide chain.
| Feature | Exonuclease | Endonuclease |
|---|---|---|
| Site of Action | Acts only at the ends (terminals) of the DNA molecule. | Acts at specific internal sites within the DNA molecule. |
| Cleavage Pattern | Removes nucleotides sequentially from the $3'$ or $5'$ end. | Creates internal nicks, gaps, or double-stranded breaks. |
| Product | Produces individual nucleotides or short oligonucleotides. | Produces fragments of various lengths (restriction fragments). |
| Specificity | Usually non-sequence specific. | Often highly sequence-specific (e.g., Restriction Endonucleases). |
2. Schematic Representation of Cleavage Sites
3. Analytical Comparison
Exonucleases: These enzymes utilize a processive mechanism to hydrolyze phosphodiester bonds starting from the free $3'$ or $5'$ hydroxyl termini. They play a vital role in DNA proofreading during replication, where DNA Polymerase I, for instance, utilizes $3' \to 5'$ exonuclease activity to excise mismatched bases [Per DNA Polymerase Fidelity Mechanisms].
Endonucleases: These enzymes recognize specific recognition sequences (palindromic sequences) and cleave the internal phosphodiester bonds. In biotechnology, Type II Restriction Endonucleases are the primary tools, as they provide high precision by cutting within the recognition site, facilitating the generation of recombinant DNA molecules [Per Recombinant DNA Technology Protocols].
4. Summary of Functional Distinction
- Exonuclease: Operates like a "trimmer," reducing the chain length from the outside inward. It does not require a specific internal sequence to initiate activity.
- Endonuclease: Operates like "molecular scissors," capable of breaking a long DNA molecule into discrete, manageable fragments based on the presence of a specific target sequence (e.g., $5'-GAATTC-3'$ for EcoRI).
Final Solution: The fundamental distinction between Exonucleases and Endonucleases lies in their point of initiation: Exonucleases degrade nucleic acids from the terminal ends (producing nucleotides), whereas Endonucleases hydrolyze phosphodiester bonds at specific internal sites (producing DNA fragments).
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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