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

Options

A. Another DNA
B. Protein synthesis
C. tRNA molecule
D. mRNA molecule

Answer

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

### Step-by-Step Solution:

1. **Understanding DNA's Role**:
- DNA (Deoxyribonucleic Acid) is the genetic material that carries the instructions for the synthesis of proteins and RNA molecules. It serves as a template for these processes.

2. **Evaluating Each Option**:
- **Option 1: Another DNA molecule**:
- DNA replication occurs when a DNA strand is copied to form another DNA strand. This process directly involves the original DNA strand.
- **Conclusion**: DNA is directly involved.

- **Option 2: tRNA molecule (transfer RNA)**:
- The synthesis of tRNA occurs through the process of transcription, where DNA is used as a template to synthesize RNA, including tRNA.
- **Conclusion**: DNA is directly involved.

- **Option 3: mRNA molecule (messenger RNA)**:
- Similar to tRNA, mRNA is synthesized from DNA during transcription. The DNA strand serves as a template for the creation of mRNA.
- **Conclusion**: DNA is directly involved.

- **Option 4: Protein synthesis**:
- Protein synthesis involves two main processes: transcription (where DNA is transcribed to mRNA) and translation (where mRNA is translated into proteins).
- While DNA is involved in the transcription of mRNA, it does not directly synthesize proteins. Instead, mRNA serves as a template for translation, which occurs in the ribosomes.
- **Conclusion**: DNA is not directly involved in the synthesis of proteins.

3. **Final Answer**:
- The correct option is **protein synthesis** because while DNA is involved in creating mRNA, it does not directly synthesize proteins.