Choose the correct statement about the direction of DNA strand

Options

A. DNA synthesis takes place in `5' to 3' ` direction on the template strand
B. DNA synthesis takes place in `3' to 5' ` direction on the new strand
C. DNA synthesis takes place in `5' to 3' ` direction on the leading strand
D. None of these

Answer

To solve the question regarding the direction of DNA strand synthesis, let’s analyze each statement provided:

1. **DNA synthesis takes place in 5 prime to 3 prime direction on template strand.**
- This statement is incorrect. While DNA synthesis does occur in the 5' to 3' direction, this refers to the newly synthesized strand, not the template strand. The template strand runs in the opposite direction (3' to 5').

2. **DNA synthesis takes place in 3 prime to 5 prime direction on new strand.**
- This statement is also incorrect. DNA synthesis always occurs in the 5' to 3' direction. Therefore, it cannot take place in the 3' to 5' direction on the new strand.

3. **DNA synthesis takes place in 5 prime to 3 prime direction on leading strand.**
- This statement is correct. The leading strand is synthesized continuously in the 5' to 3' direction as the DNA unwinds.

4. **None of this.**
- This option is incorrect since we have identified a correct statement.

Based on the analysis of the statements, the correct answer is:

**DNA synthesis takes place in 5 prime to 3 prime direction on leading strand.**

### Step-by-Step Solution:
1. **Understand DNA Directionality:**
- DNA strands have a directionality indicated by 5' and 3' ends. The 5' end has a phosphate group, while the 3' end has a hydroxyl group.

2. **Identify the Template and New Strands:**
- During DNA replication, the template strand runs in the 3' to 5' direction, while the new strand is synthesized in the 5' to 3' direction.

3. **Evaluate Each Statement:**
- Analyze each statement regarding the direction of synthesis and identify which is true based on the understanding of DNA replication.

4. **Select the Correct Statement:**
- The only correct statement is that DNA synthesis occurs in the 5' to 3' direction on the leading strand.