During DNA synthesis, both strands require an RNA primer to start elongation because it is an

Options

A. RNA polymerase that synthesizes short stretches of RNA
B. RNA ATPase that synthesizes short stretches of complementary DNA
C. DNA polymerase that synthesizes short stretches of DNA
D. DNA ATPase that synthesizes short stretches of complementary RNA

Answer

To answer the question, "During DNA synthesis, both strands require an RNA primer to start elongation because it is an...", we need to analyze the options provided and understand the role of RNA primers in DNA synthesis.

### Step-by-Step Solution:

1. **Understanding DNA Synthesis**:
- DNA synthesis occurs during replication, where the DNA double helix unwinds, and new strands are formed.

2. **Role of RNA Primers**:
- DNA polymerases, the enzymes responsible for synthesizing new DNA strands, cannot initiate synthesis on their own. They require a short segment of RNA, known as a primer, to provide a free 3' hydroxyl (-OH) group to which new DNA nucleotides can be added.

3. **Identifying the Correct Enzyme**:
- The question asks why RNA primers are necessary. The answer lies in the function of the enzyme that synthesizes these primers.
- The enzyme responsible for synthesizing RNA primers is called **primase**, which is a type of RNA polymerase that synthesizes short stretches of RNA complementary to the DNA template.

4. **Evaluating the Options**:
- **Option A**: RNA polymerase that synthesizes short stretches of RNA - This is correct because primase is a type of RNA polymerase.
- **Option B**: RNA A to B that synthesizes short stretches of complementary DNA - This is incorrect as it does not accurately describe the function of any known enzyme.
- **Option C**: DNA polymerase that synthesizes short stretches of DNA - This is incorrect because DNA polymerase cannot initiate synthesis without a primer.
- **Option D**: DNA A to B that synthesizes short stretches of complementary DNA - This is also incorrect as it does not describe a known enzyme.

5. **Conclusion**:
- The correct answer is **Option A**: RNA polymerase that synthesizes short stretches of RNA. This is because the RNA primer is synthesized by primase, which is a type of RNA polymerase.

### Final Answer:
**During DNA synthesis, both strands require an RNA primer to start elongation because it is an RNA polymerase that synthesizes short stretches of RNA.**