A DNA strand is directly involved in the synthesis of all the following except :

Options

A. t-RNA molecule
B. m-RNA molecule
C. another DNA strand
D. protein synthesis

Answer

To solve the question "A DNA strand is directly involved in the synthesis of all the following except:", we will analyze each option provided in the context of molecular biology.

### Step-by-Step Solution:

1. **Identify the Options**: The question implies that there are several options related to the synthesis of molecules. We need to determine which of these processes does not involve DNA directly.

2. **Analyze RNA Synthesis**:
- **mRNA Synthesis**: DNA serves as a template for the synthesis of mRNA through a process called transcription. Therefore, DNA is directly involved in the synthesis of mRNA.
- **tRNA and rRNA Synthesis**: Similarly, other types of RNA (like tRNA and rRNA) are also synthesized using DNA as a template. Thus, DNA is directly involved in the synthesis of all RNA types.

3. **Analyze DNA Replication**:
- **DNA Replication**: During DNA replication, each strand of the original DNA molecule serves as a template for the synthesis of a new complementary strand. This process is known as semi-conservative replication. Thus, DNA is directly involved in the synthesis of another DNA strand.

4. **Analyze Protein Synthesis**:
- **Protein Synthesis**: The process of protein synthesis involves mRNA, tRNA, and ribosomes, but not DNA directly. While DNA contains the genetic information that is transcribed into mRNA, the actual synthesis of proteins occurs at the ribosome, where mRNA is translated into a polypeptide chain. Therefore, DNA is indirectly involved in protein synthesis.

5. **Conclusion**: Based on the analysis, the correct answer to the question is that DNA is not directly involved in protein synthesis.

### Final Answer:
A DNA strand is directly involved in the synthesis of all the following except **protein synthesis**.

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