Synthesis of leading and lagging strand require

Options

A. Single primer
B. Single and many primers respectively
C. Many and single primers respectively
D. Many primers

Answer

### Step-by-Step Solution:

1. **Understanding DNA Replication**: DNA replication occurs at the replication fork, where the double-stranded DNA unwinds into two single strands. Each strand serves as a template for the synthesis of a new strand.

2. **Identifying the Strands**: The two strands of DNA are oriented in opposite directions (anti-parallel). One strand runs in the 3' to 5' direction (template for the leading strand), while the other runs in the 5' to 3' direction (template for the lagging strand).

3. **Role of DNA Polymerase**: The enzyme responsible for synthesizing new DNA strands is DNA-dependent DNA polymerase. This enzyme can only synthesize DNA in the 5' to 3' direction.

4. **Synthesis of the Leading Strand**:
- The leading strand is synthesized continuously in the direction of the replication fork.
- It requires only **one RNA primer** to initiate synthesis.
- The DNA polymerase adds nucleotides to the 3' end of the RNA primer, extending the new DNA strand continuously.

5. **Synthesis of the Lagging Strand**:
- The lagging strand is synthesized discontinuously, away from the replication fork.
- It requires **multiple RNA primers** because the synthesis occurs in short segments called Okazaki fragments.
- Each Okazaki fragment starts with an RNA primer, and DNA polymerase synthesizes DNA in the 5' to 3' direction until it reaches the next RNA primer.

6. **Final Steps**: After the synthesis of the lagging strand, the RNA primers are removed and replaced with DNA. The Okazaki fragments are then joined together by the enzyme DNA ligase to form a continuous strand.

7. **Conclusion**: In summary, the leading strand requires **one primer**, while the lagging strand requires **many primers** for its synthesis.

### Answer:
The synthesis of the leading strand requires **one primer**, while the synthesis of the lagging strand requires **many primers**.