Primers used in PCR must be:
(a) 3'-end specific
(b) 5'-end specific
(c) It can be 3'-end specific or 5'-end specific.
(d) Primers are not needed in PCR.

Options

A. 3'-end specific
B. 5'-end specific
C. It can be 3'-end specific or 5'-end specific.
D. Primers are not needed in PCR.

Answer

To solve the question regarding the specificity of primers used in PCR (Polymerase Chain Reaction), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Role of Primers in PCR**:
- Primers are short sequences of nucleotides that provide a starting point for DNA synthesis during PCR. They are essential for the amplification of a specific DNA segment.

2. **Types of Primers**:
- In PCR, two types of primers are typically used:
- **Forward Primer**: Binds to the start of the target DNA sequence.
- **Reverse Primer**: Binds to the complementary strand of the target DNA.

3. **Specificity of Primers**:
- Primers can be designed to be specific to either the 3'-end or the 5'-end of the target DNA sequence.
- The 3'-end specificity is crucial because DNA polymerase extends the primer from its 3' end, synthesizing new DNA in the 5' to 3' direction.

4. **Evaluating the Options**:
- (a) 3'-end specific: This is partially correct, as primers do need to be specific to the 3' end to allow for DNA synthesis.
- (b) 5'-end specific: This is incorrect, as the primer must bind to the 3' end for synthesis.
- (c) It can be 3'-end specific or 5'-end specific: This is correct, as primers can be designed based on the specific needs of the PCR process.
- (d) Primers are not needed in PCR: This is incorrect, as primers are essential for the PCR process.

5. **Conclusion**:
- The correct answer is (c) It can be 3'-end specific or 5'-end specific.

### Final Answer:
(c) It can be 3'-end specific or 5'-end specific.

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