Which of the following is incorrect about nucleosome ?

Options

A. Histones are organized to form a unit of eight molecules called a histone octamer
B. The negatively charged DNA is wrapped around the positively charged histone ostamer .
C. Nucleosome constitute the repeating unit of a structure in nucleus called chromatin
D. The nucleosome in chromatin are seen as 'Beads on string' structure when viewed under light microscope .

Answer

To determine which statement about nucleosomes is incorrect, we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Understanding Nucleosomes**: Nucleosomes are the fundamental units of chromatin, consisting of DNA wrapped around a core of histone proteins. Each nucleosome consists of a histone octamer and approximately 146 base pairs of DNA.

2. **Analyzing the First Statement**:
- **Statement**: Histones are organized to form a unit of eight molecules called the histone octamer.
- **Evaluation**: This statement is correct. The histone octamer is indeed made up of eight histone proteins (two copies each of H2A, H2B, H3, and H4).

3. **Analyzing the Second Statement**:
- **Statement**: The negatively charged DNA is wrapped around the positively charged histone octamer.
- **Evaluation**: This statement is also correct. DNA has a negative charge due to its phosphate backbone, and it wraps around the positively charged histones.

4. **Analyzing the Third Statement**:
- **Statement**: Nucleosomes constitute the repeating unit of the structure in the nucleus called chromatin.
- **Evaluation**: This statement is correct as well. Nucleosomes are indeed the repeating units that make up chromatin.

5. **Analyzing the Fourth Statement**:
- **Statement**: The nucleosome in chromatin are seen as the bead-on-the-string structure when viewed under the light microscope.
- **Evaluation**: This statement is incorrect. The bead-on-a-string structure of nucleosomes can only be visualized under an electron microscope, not a light microscope.

### Conclusion:
The incorrect statement about nucleosomes is the fourth one.

### Final Answer:
**The incorrect statement about nucleosomes is: "The nucleosome in chromatin are seen as the bead-on-the-string structure when viewed under the light microscope."**

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