Protein synthesis in an animal cell occurs

Options

A. only on the ribosomes present in cytosol
B. on ribosomes present in cytoplasm as well as in mitochondria
C. only on ribosomes attached to the nuclear envelope and endoplasmic reticulum
D. On ribosomes present in the nucleolus as well as in cytoplasm

Answer

### Step-by-Step Solution:

1. **Understanding Protein Synthesis**: Protein synthesis is the process through which cells generate proteins. This process involves two main stages: transcription and translation.

2. **Central Dogma of Molecular Biology**: The central dogma describes the flow of genetic information from DNA to RNA to protein.
- **Transcription**: The first step where DNA is converted into messenger RNA (mRNA).
- **Translation**: The second step where mRNA is translated into a protein.

3. **Location of Translation**: The translation process, which is part of protein synthesis, primarily occurs in the cytoplasm of the cell.

4. **Role of Ribosomes**: Ribosomes are essential for protein synthesis as they are the sites where amino acids are assembled into proteins.
- Ribosomes can be found free-floating in the cytoplasm or attached to the endoplasmic reticulum (ER), forming what is known as rough endoplasmic reticulum (RER).

5. **Mitochondrial Protein Synthesis**: It's important to note that mitochondria also contain their own ribosomes and can synthesize some proteins independently. However, the majority of protein synthesis in animal cells occurs in the cytoplasm.

6. **Other Options**:
- **Cytosol**: While it is the fluid part of the cytoplasm, protein synthesis specifically occurs at ribosomes.
- **Nucleolus**: This is primarily involved in ribosome production, not protein synthesis.
- **Nuclear Envelope**: Ribosomes are not attached to the nuclear envelope; they are associated with the endoplasmic reticulum.

7. **Conclusion**: Therefore, the primary site of protein synthesis in an animal cell is the cytoplasm, specifically at the ribosomes.

### Final Answer:
Protein synthesis in an animal cell occurs primarily in the cytoplasm, specifically at the ribosomes.

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