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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance4 Marks
Question
Explain with diagram - Hershey and Chase experiment.###On the basis of experimental proof explain the diagram that DNA is genetic material.###How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?
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Answer

→ The unequivocal proof that DNA is the genetic material came from the experiments of Alfred Hershey and Martha Chase (1952). They worked with viruses that infect bacteria called bacteriophages.
→ The bacteriophage attaches to the bacteria and its genetic material then enters the bacterial cell.
→ The bacterial cell treats the viral genetic material as if it was its own and subsequently manufactures more virus particles.
→ Hershey and Chase worked to discover whether it was protein or DNA from the viruses that entered the bacteria.
→ They grew some viruses on a medium that contained radioactive phosphorus and some others on medium that contained radioactive sulfur.
→ Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but protein does not.
→ Similarly, viruses grown on radioactive sulfur contained radioactive protein but not radioactive DNA because DNA does not contain sulfur.
→ Radioactive phages were allowed to attach to E.coli bacteria.
→ Then, as the infection proceeded, the viral coats were removed from the bacteria by agitating them in a blender.
→ The virus particles were separated from the bacteria by spinning them in a centrifuge.
→ Bacteria which was infected with viruses that had radioactive DNA were radioactive, indicating that DNA was the material that passed from the virus to the bacteria.
→ Bacteria that were infected with viruses that had radioactive proteins were not radioactive.
→ This indicates that proteins did not enter the bacteria from the viruses.
→ DNA is therefore the genetic material that is passed from virus to bacteria.
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Restriction endonuclease was isolated for the first ti me by W. Arb er in 1962 in bacteria. Restriction endonucleases cut the DNA duplex at specific points therefore they are also called as molecular scissors or biological scissors. Three types of restriction endonucleases are Type I, Type II and Type III but only Type II restriction endonucleases are used in recombinant DNA technology. Restriction endonuclease EcoR I recognises the base sequence GAATTC in DNA duplex and cut strands between G and A.

  1. Only type II restriction enzymes are used in gene manipulation because
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  3. It makes cleavage or cut in both the strands of DNA molecule.
  4. Both (a) and (c).
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  3. Na2+ ions
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  1.  Restriction endonuclease was isolated for the first time in a:
  1. Plant cell.
  2. Animal cell.
  3. Prokaryotic cell.
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  1. $\ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

  2. $ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

  3. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \uparrow$

  4. $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \downarrow\\5'-\text{GAATTC}-3'\\3'-\text{CTTAAG}-5'\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \uparrow$

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Y
Z
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  1. Both assertion and reason are true, and reason is the correct explanation of assertion.
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  3. Pollen grain Z lacks protrusions that allow it to adhere properly onto the stigma surface.
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  4. The flower petals are brightly colored.
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Reerna, Jai and Ankit are suffering from autoimmune diseases of adrenal cortex, joints and thyroid gland, respectively. Their immune system failed to recognise self and non-self and started destroying their body's own proteins. They are seeking proper medical help for their conditions but their condition cannot be cured completely.

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  3. Destruction of beta cells, leading to undersecretion of insulin.
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