There are 5 test tubes having a culture medium containing rough colonies of streptococcus pneumoniae. The following substances were added in them. Which of these test tubes will show smooth colonies of streptococcus pneumoniae on incubation for some time?
Test tube I: RNA from a heat-killed smooth strain of streptococcus pneumoniae
Test tube II: DNA from a heat-killed smooth strain of streptococcus pneumoniae
Test tube III: Protein from a heat-killed smooth strain of streptococcus pneumoniae
Test tube IV: Carbohydrate from a heat-killed smooth strain of streptococcus pneumoniae
Test tube V: Heat killed smooth strain of streptococcus pneumoniae incubated with DNAse enzyme

Options

A. II and V
B. II , III and IV
C. I and II
D. II

Answer

To solve the question regarding which test tube will show smooth colonies of Streptococcus pneumoniae after incubation, we need to analyze the role of each substance added to the test tubes in relation to the transformation principle discovered by Griffith and later confirmed by Avery, MacLeod, and McCarty.

### Step-by-Step Solution:

1. **Understanding the Background**:
- Streptococcus pneumoniae has two strains: the rough (R) strain, which is non-virulent, and the smooth (S) strain, which is virulent due to its polysaccharide coat.
- Griffith's experiment demonstrated that the R strain could be transformed into the S strain when exposed to heat-killed S strain bacteria, indicating the presence of a "transforming principle."

2. **Identifying the Transforming Principle**:
- Avery, MacLeod, and McCarty identified that the transforming principle is DNA, which is responsible for the transformation of R strain into S strain.

3. **Analyzing Each Test Tube**:
- **Test Tube I**: Contains RNA from a heat-killed smooth strain.
- **Conclusion**: RNA cannot transform the R strain into S strain. **(No smooth colonies)**

- **Test Tube II**: Contains DNA from a heat-killed smooth strain.
- **Conclusion**: DNA is the transforming principle and will transform the R strain into S strain. **(Smooth colonies will appear)**

- **Test Tube III**: Contains protein from a heat-killed smooth strain.
- **Conclusion**: Proteins do not have the ability to transform the R strain into S strain. **(No smooth colonies)**

- **Test Tube IV**: Contains carbohydrate from a heat-killed smooth strain.
- **Conclusion**: Carbohydrates do not have the ability to transform the R strain into S strain. **(No smooth colonies)**

- **Test Tube V**: Contains heat-killed smooth strain incubated with DNase enzyme.
- **Conclusion**: DNase will degrade the DNA, preventing transformation. **(No smooth colonies)**

4. **Final Conclusion**:
- The only test tube that will show smooth colonies of Streptococcus pneumoniae after incubation is **Test Tube II**, which contains DNA from a heat-killed smooth strain.

### Answer:
**Test Tube II** will show smooth colonies of Streptococcus pneumoniae.

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