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Q12(a):
Discuss with your teacher and find out how to distinguish between
(a) Plasmid DNA and Chromosomal DNA
Solution :
Step 1: Theoretical Foundation of Genomic vs. Extrachromosomal DNA
To distinguish between Plasmid DNA and Chromosomal DNA, one must evaluate their structural organization, function, and replication mechanisms within a prokaryotic cell (typically Escherichia coli). Chromosomal DNA represents the primary genetic blueprint essential for survival, whereas Plasmid DNA acts as an auxiliary genetic element providing selective advantages.
Step 2: Comparative Analytical Matrix
| Characteristic | Chromosomal DNA | Plasmid DNA |
|---|---|---|
| Biological Function | Encodes essential proteins for metabolism, growth, and reproduction. | Encodes non-essential auxiliary traits (e.g., antibiotic resistance, fertility). |
| Molecular Structure | Large, linear or circular, highly condensed within the nucleoid region. | Small, circular, double-stranded, supercoiled DNA. |
| Replication | Dependent on the cell cycle; occurs once per cell division. | Independent of chromosomal replication; possesses an ori (origin of replication). |
| Copy Number | Usually one per cell (monoploid). | Varies (1 to hundreds per cell). |
Step 3: Visual Representation of DNA Topology
Step 4: Distinguishing Methodologies in a Laboratory Setting
In a biotechnology laboratory, these two forms are distinguished via the following physical and chemical criteria:
- Alkaline Lysis Method: [Per the mechanism of differential denaturation], when cellular lysate is treated with an alkaline solution ($pH \approx 12-12.5$), high-molecular-weight chromosomal DNA denatures irreversibly. Conversely, small, supercoiled plasmid DNA remains partially base-paired. Upon neutralization with potassium acetate, the chromosomal DNA forms an insoluble complex with proteins, while plasmids remain in the supernatant [Ref: Birnboim & Doly, 1979].
- Gel Electrophoresis: Upon loading the sample into an agarose gel, the molecules migrate based on size (base pairs). Chromosomal DNA is significantly larger ($> 4,000,000$ bp) and will remain near the loading well, whereas plasmid DNA ($1,000$ to $200,000$ bp) will migrate faster, allowing for distinct band separation [By the principle of molecular sieving].
- Density Gradient Centrifugation: Using Ethidium Bromide ($EtBr$) in a Cesium Chloride ($CsCl$) gradient, plasmid DNA binds less dye than linear chromosomal DNA due to its supercoiled state, resulting in a distinct, lower buoyant density band [Ref: Principle of Isopycnic Centrifugation].
Final Solution: Plasmid DNA and Chromosomal DNA are distinguished by their size (chromosomal being significantly larger), copy number (chromosomal being single-copy, plasmid being multi-copy), functional dependency (chromosomal being essential, plasmid being accessory), and their specific behavior during alkaline denaturation and agarose gel electrophoresis.
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(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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