In bacterial transformation, naked DNA from a lysed donor bacterium enters a competent recipient cell. Which organism was used in Griffith's classic experiment demonstrating transformation, and what was the transforming principle identified by Avery, MacLeod, and McCarty?
- A Haemophilus influenzae; the transforming principle is RNA
- B Streptococcus pneumoniae; the transforming principle is DNA (deoxyribonucleic acid), demonstrated by DNase sensitivity of transforming activity ✓
- C Streptococcus pneumoniae; the transforming principle is protein (polysaccharide capsule)
- D Bacillus subtilis; the transforming principle is plasmid DNA only
Correct answer: B. Streptococcus pneumoniae; the transforming principle is DNA (deoxyribonucleic acid), demonstrated by DNase sensitivity of transforming activity
Explanation
Griffith (1928) used Streptococcus pneumoniae (smooth/rough strains) to show heat-killed smooth S + live rough R produced virulent S — the 'transforming principle.' Avery, MacLeod, and McCarty (1944) identified the transforming principle as DNA by showing: protease and RNase treatment did not destroy transforming activity, but DNase treatment abolished it completely, proving DNA is the hereditary material. This remains a landmark experiment in molecular biology.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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