Proteinaceous infectious particles causing diseasea are

Options

A. Prions
B. Viroids
C. Viruses
D. Chlamydia.

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the name of proteinaceous infectious particles that cause diseases.

2. **Identifying Key Terms**: The term "proteinaceous infectious particles" indicates that we are looking for a type of infectious agent that is primarily made up of proteins.

3. **Defining Prions**: Prions are defined as infectious agents composed solely of protein. They are known to cause various neurodegenerative diseases in both animals and humans. Importantly, prions do not contain any nucleic acids (DNA or RNA).

4. **Evaluating Other Options**:
- **Viroids**: These are small infectious agents that consist of RNA but lack a protein coat. Therefore, they do not fit the description of being proteinaceous.
- **Viruses**: Viruses contain nucleic acids (either DNA or RNA) and are surrounded by a protein coat. They do not fit the definition of being solely proteinaceous.
- **Chlamydia**: This is a type of bacteria and does not fit the definition of a proteinaceous infectious particle.

5. **Conclusion**: Based on the definitions and characteristics of prions, the correct answer to the question is "prions".

### Final Answer:
The proteinaceous infectious particles causing diseases are known as **prions**.

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