In the year 1963 , the two enzymes responsible for restricting the growth of bacteriophage in Escherichia coli were isolated . They were respectively

Options

A. a.Ligase, restriction endonuclease
B. b.Helicase, restriction endonuclease
C. c.Methylase, restriction endonuclease
D. d.DNA polymerase, restriction endonuclease

Answer

**Step-by-Step Solution:**

1. **Understanding the Context**: The question refers to the year 1963 when two specific enzymes were isolated that play a role in restricting the growth of bacteriophages in Escherichia coli (E. coli). Bacteriophages are viruses that infect bacteria.

2. **Identifying the Enzymes**: The two enzymes that were isolated are:
- **Methylase**: This enzyme adds methyl groups to specific bases in the DNA. This methylation helps protect the host DNA from being cut by restriction endonucleases.
- **Restriction Endonuclease**: This enzyme cuts DNA at specific sequences. In the context of E. coli, it recognizes foreign DNA (such as that from bacteriophages) and cleaves it to prevent infection.

3. **Function of the Enzymes**:
- **Methylase**: Protects the host DNA by modifying it, making it unrecognizable to restriction endonucleases.
- **Restriction Endonuclease**: Acts as a defense mechanism by cutting foreign DNA, thereby preventing the bacteriophage from replicating within the E. coli.

4. **Conclusion**: The two enzymes responsible for restricting the growth of bacteriophages in E. coli, which were isolated in 1963, are Methylase and Restriction Endonucleases.

**Final Answer**: Methylase and Restriction Endonucleases.

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