Question:

In Griffith's experiment, a mixture of heat- killed virulent bacteria $R$ and live non-virulent bacteria $S$, lead to the death of mice. 'Transforming principle' got transferred from heat-killed $R$ strain to $S$ strain and made it virulent.

Updated On: Jul 6, 2022
  • If both assertion and reason are true and reason is the correct explanation of assertion
  • If both assertion and reason are true but reason is not the correct explanation of assertion
  • If assertion is true but reason is false
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The Correct Option is D

Solution and Explanation

When bacteria Streptococcus pneumoniae are grown on a culture plate, some produce smooth shiny colonies $(S)$ while others produce rough colonies $(R)$. This is because the $S$ strain bacteria have a mucous (polysaccharide) coat, while $R$ strain does not. Mice infected with the $S$ strain (virulent) die from pneumonia infection but mice infected with the $R$ strain do not develop pneumonia. In Griffith's experiement, some 'transforming principle', transferred from the heat-killed $S$ strain, had enabled the $R$ strain to synthesise a smooth polysaccharide coat and become virulent which must be due to the transfer of the genetic material. This is known as transformation.
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Notes on the molecular basis of inheritance

Concepts Used:

The Molecular Basis of Inheritance

DNA Replication:

DNA synthesis is commenced at particular points within the DNA strand referred to as ‘origins’, which are certain coding regions. There are numerous origin sites, and when replication of DNA starts, these sites are mentioned as replication forks. Within the replication, the complex is the enzyme DNA Helicase, so that they can be utilized as a template for replication. DNA Primase is another enzyme that's essential in DNA replication.

RNA:

Ribonucleic acid (RNA) is an essential biological macromolecule that exists all together in biological cells. It is principally involved in the synthesis of proteins, that carry the messenger instructions from DNA, which itself contains the genetic instructions needed for the event and maintenance of life. In some viruses, RNA, in spite of DNA, carries genetic information.

Genetic Code:

Genetic code is the term we use in the manner that the four bases of DNA--the A, C, G, and Ts--are strung together in a way that the ribosome, the cellular machinery, can read them and switch them into a protein. In the ordering, every three nucleotides during a row count as a triplet and code for one amino alkanoic acid.

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