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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?
Solution :
1. Conceptual Foundation of Reporter Systems
In recombinant DNA technology, a reporter gene is a nucleotide sequence that encodes a protein (enzyme) that produces a quantifiable, observable phenotype—typically fluorescence, luminescence, or color change—when expressed in a host cell. Unlike selectable markers (e.g., antibiotic resistance genes), which facilitate the survival of transformants under selective pressure [Per Principles of Selection], reporter genes serve to monitor the spatial expression or the efficiency of gene delivery.
2. Mechanism of Reporter Enzyme Action
Reporter enzymes facilitate the identification of successfully transformed cells by converting a non-detectable substrate into a detectable product. The fundamental equation for the reporter enzyme reaction is:
$[Substrate]_{non-detectable} + [Reporter Enzyme]_{expressed} \xrightarrow{Catalysis} [Product]_{detectable} + [Byproducts]$
Common examples include the lacZ gene (coding for $\beta$-galactosidase) and the gfp gene (Green Fluorescent Protein).
3. Comparative Analysis: Selectable Marker vs. Reporter Gene
| Feature | Selectable Marker | Reporter Gene |
|---|---|---|
| Primary Role | Survival/Elimination | Observation/Quantification |
| Outcome | Binary (Dead or Alive) | Visual/Biochemical readout |
| Host interaction | Confers resistance | Confers metabolic or optical trait |
4. Procedural Implementation: The β-galactosidase Assay
The lacZ gene is a classic reporter used to monitor transformation via blue-white screening:
- Step A (Construction): The foreign DNA is inserted into the lacZ gene site within the vector [Per Insertional Inactivation].
- Step B (Substrate Addition): Chromogenic substrates like X-gal ($5\text{-bromo-}4\text{-chloro-}indolyl\text{-}\beta\text{-}D\text{-galactopyranoside}$) are added to the growth medium.
- Step C (Detection):
- If the host cell lacks the recombinant plasmid, the enzyme is produced $\rightarrow$ Blue colonies.
- If the foreign DNA is successfully inserted (disrupting lacZ), no active enzyme is produced $\rightarrow$ White colonies.
5. Visualizing the Reporter Logic
6. Analytical Conclusion
The reporter enzyme provides an additional layer of verification. While the selectable marker (e.g., $Amp^R$) ensures that only cells containing the plasmid survive, the reporter gene allows the researcher to differentiate between cells carrying the vector only and cells carrying the recombinant construct. This dual-layer system significantly increases the precision of transgenic screening [Per Biotechnology Quality Control Standards].
Final Solution: A reporter enzyme monitors transformation by generating a visual phenotype (such as color or fluorescence) when its gene is expressed. By utilizing insertional inactivation, the reporter gene can distinguish between successful recombinant hosts (where the reporter is interrupted/silent) and non-recombinant hosts (where the reporter is active), functioning alongside selectable markers to ensure high experimental stringency.
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?
- 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
- 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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