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E. Coli about to replicate was placed in...

E. Coli about to replicate was placed in a medium containing radio active thymidine for five minutes. Then it was made to replicate in a normal medium. Which of the following observation shall be correct : -

A

Both the strands of DNA will be radio active

B

One strand radio active

C

Each strand half radio active

D

None is radio active

Text Solution

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The correct Answer is:
To solve the question regarding the E. coli experiment with radioactive thymidine, we can break down the process step by step: ### Step 1: Understanding the Experiment E. coli was placed in a medium containing radioactive thymidine for five minutes. Thymidine is a nucleoside that is a building block of DNA. The radioactive thymidine will be incorporated into the DNA during replication. **Hint:** Remember that thymidine is a component of DNA, and its incorporation into DNA will help us track which strands are newly synthesized. ### Step 2: Mechanism of DNA Replication DNA replication is a semi-conservative process. This means that during replication, each of the two strands of the original DNA molecule serves as a template for the new strands. After replication, each new DNA molecule consists of one old (parent) strand and one newly synthesized strand. **Hint:** Focus on the semi-conservative nature of DNA replication, which is crucial for understanding how the radioactive thymidine will be distributed. ### Step 3: Analyzing the Result After Replication After the E. coli was placed in the radioactive medium, it would replicate its DNA, incorporating the radioactive thymidine into the newly synthesized strands. When the cells are then placed in a normal medium, they will continue to replicate, but the new strands will not incorporate any more radioactive thymidine. **Hint:** Consider what happens to the strands after the initial incorporation of the radioactive thymidine and how they will behave in subsequent replications. ### Step 4: Determining the Observations Since the original DNA strand (the parent strand) was not exposed to radioactive thymidine after the first five minutes, it will not be radioactive. The newly synthesized strand will contain the radioactive thymidine. Therefore, after the replication process, we will have one radioactive strand (the newly synthesized strand) and one non-radioactive strand (the original template). **Hint:** Think about the implications of semi-conservative replication: one strand will always be the original, and one will always be newly synthesized. ### Conclusion Based on the above analysis, the correct observation is that **one strand of the newly synthesized DNA will be radioactive** while the other strand (the parent strand) will not be radioactive. Thus, the correct answer is: **Option 2: One strand radioactive.**
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