In almost all cases polypeptides are synthesized :

Options

A. on ribosomes
B. directly off DNA
C. within mitochondria
D. in the nucleus

Explanation

To answer the question "In almost all cases, polypeptides are synthesized:", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question is asking where polypeptides are synthesized in the cell. Polypeptides are chains of amino acids that make up proteins.

2. **Identify the Options**: The options provided are:
- A) On ribosomes
- B) Directly from DNA
- C) With mitochondria
- D) In the nucleus

3. **Analyze Each Option**:
- **Option A (On ribosomes)**: Ribosomes are known as the protein factories of the cell. They are the sites where translation occurs, leading to the synthesis of polypeptides from mRNA.
- **Option B (Directly from DNA)**: While DNA contains the genetic information for proteins, polypeptides are not synthesized directly from DNA. Instead, DNA is transcribed into mRNA, which is then translated into polypeptides.
- **Option C (With mitochondria)**: Mitochondria do have their own ribosomes and can synthesize some proteins, but this is not the primary site for polypeptide synthesis in the cell.
- **Option D (In the nucleus)**: The nucleus is where transcription occurs (the process of making mRNA from DNA), but polypeptide synthesis does not occur here.

4. **Conclusion**: Based on the analysis, the correct answer is **Option A: On ribosomes**. This is where the synthesis of polypeptides occurs through the process of translation.

### Final Answer:
Polypeptides are synthesized **on ribosomes**.

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