Thermococcus, Methanococcus and Methanobacterium are

Options

A. archaebacteria having eukaryotic histone homologue
B. bacteria with cytoskeleton
C. archaebacteria with negatively supercoiled DNA as in eukaryotes but lacking histones
D. bacteria with positively coiled DNA, cytoskeleton and mitochondria

Answer

To solve the question regarding Thermococcus, Methanococcus, and Methanobacterium, we can break it down step by step:

### Step-by-Step Solution:

1. **Identify the Organisms**:
- Thermococcus, Methanococcus, and Methanobacterium are all classified under the domain Archaea. They are known as archaebacteria.

2. **Characteristics of Archaebacteria**:
- Archaebacteria are distinct from eubacteria (true bacteria) in several ways. They can survive in extreme environments, such as high temperatures and high salinity.
- They do not have peptidoglycan in their cell walls, which is a characteristic feature of eubacteria.

3. **DNA Structure**:
- The DNA in archaebacteria is negatively supercoiled, similar to that found in eukaryotes. This means that the DNA is twisted in a way that is opposite to the direction of the double helix.
- However, archaebacteria lack histones, which are proteins that help package DNA in eukaryotes.

4. **Evaluating the Options**:
- **Option A**: Archaebacteria having eukaryotic histone homolog - Incorrect, because they lack histones.
- **Option B**: Bacteria with cytoskeleton - Incorrect, as they are archaebacteria and do not have a cytoskeleton like eukaryotes.
- **Option C**: Archaebacteria with negatively supercoiled DNA as in eukaryotes but lacking histones - Correct, as this accurately describes their DNA structure.
- **Option D**: Bacteria with positively coiled DNA, cytoskeleton, and mitochondria - Incorrect, as they do not have these features.

5. **Conclusion**:
- Based on the characteristics and the evaluation of the options, the correct answer is **Option C**: Archaebacteria with negatively supercoiled DNA as in eukaryotes but lacking histones.