DNA replication is continuous

Options

A. On the template with polarity 3. `to` 5.
B. On the template with polarity 5. `to` 3.
C. On both the templates
D. On none of the templates

Answer

**Step-by-Step Solution:**

1. **Understanding DNA Replication**: DNA replication is the process by which a cell duplicates its DNA before cell division. It involves unwinding the double helix and synthesizing new strands complementary to the original strands.

2. **Direction of Synthesis**: DNA polymerase, the enzyme responsible for synthesizing new DNA strands, can only add nucleotides in the 5' to 3' direction. This means that the new strand is synthesized by adding nucleotides to the 3' end of the growing strand.

3. **Template Strand Polarity**: The original DNA strands are anti-parallel, meaning one strand runs in the 5' to 3' direction while the complementary strand runs in the 3' to 5' direction. During replication, the strand that runs 3' to 5' serves as the template for continuous synthesis.

4. **Continuous vs. Discontinuous Replication**: DNA replication is continuous on the template strand that runs 3' to 5'. This is because the DNA polymerase can continuously add nucleotides in the 5' to 3' direction. The other strand, which runs 5' to 3', is synthesized in fragments (Okazaki fragments) and is therefore considered discontinuous.

5. **Evaluating the Options**:
- **Option A (3 to 5)**: This is correct as replication is continuous on the template with polarity 3' to 5'.
- **Option B (5 to 3)**: Incorrect, as replication cannot be continuous on a template running 5' to 3'.
- **Option C (both templates)**: Incorrect, as only the 3' to 5' template allows for continuous replication.
- **Option D (none of the templates)**: Incorrect, as we have established that replication is indeed continuous on the 3' to 5' template.

6. **Conclusion**: The correct answer is Option A, which states that DNA replication is continuous on the template with polarity 3 to 5.

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