In mammals, the mitochondrial ribosomes are :-

Options

A. 55s
B. 70s
C. 80s
D. 100s

Answer

To answer the question "In mammals, the mitochondrial ribosomes are:", we will analyze the options provided and determine the correct sedimentation coefficient for mitochondrial ribosomes in mammals.

### Step-by-Step Solution:

1. **Understanding Mitochondrial Ribosomes**:
- Mitochondrial ribosomes are unique compared to cytoplasmic ribosomes. They are involved in protein synthesis within the mitochondria.

2. **Identifying the Sedimentation Coefficient**:
- The sedimentation coefficient (S) is a measure of how fast a particle sediments when subjected to centrifugal force. It is expressed in Svedberg units (S).

3. **Analyzing the Options**:
- **Option 1: 55S**: This is the correct answer. Mitochondrial ribosomes in mammals consist of a small subunit (28S) and a large subunit (39S), which combine to form a 55S ribosome.
- **Option 2: 70S**: This option is incorrect. While 70S ribosomes are found in prokaryotes, they are not the type found in mammalian mitochondria.
- **Option 3: 80S**: This option is also incorrect. 80S ribosomes are characteristic of eukaryotic cytoplasmic ribosomes, not mitochondrial ribosomes.
- **Option 4: 100S**: This option is incorrect as well. There are no mitochondrial ribosomes with a sedimentation coefficient of 100S.

4. **Conclusion**:
- Based on the analysis, the correct answer is **55S** for mitochondrial ribosomes in mammals.

### Final Answer:
In mammals, the mitochondrial ribosomes are **55S**.