Total number of histone proteins present in chromatin with 20 nucleosomes

Options

A. 180
B. 80
C. 160
D. 21

Answer

To find the total number of histone proteins present in chromatin with 20 nucleosomes, follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of a Nucleosome**:
- Each nucleosome consists of an octamer of histone proteins. This octamer is made up of 8 histone proteins: 2 of each type H2A, H2B, H3, and H4.

2. **Calculate Histone Proteins in Nucleosomes**:
- Since there are 20 nucleosomes, and each nucleosome contains 8 histone proteins, we can calculate the total histone proteins from the nucleosomes:
\[ \text{Total histones from nucleosomes} = 20 \text{ nucleosomes} \times 8 \text{ histones/nucleosome} = 160 \text{ histones} \]

3. **Consider Linker Histones**:
- In addition to the histones in the nucleosomes, there are linker histones (H1) that connect the nucleosomes. For 20 nucleosomes, there will be 19 linker histones (since there is one less linker histone than the number of nucleosomes).

4. **Calculate Total Histone Proteins**:
- Now, we add the number of linker histones to the total from the nucleosomes:
\[ \text{Total histones} = 160 \text{ (from nucleosomes)} + 19 \text{ (linker histones)} = 179 \text{ histones} \]

5. **Round to Nearest Option**:
- The total number of histone proteins calculated is 179. Since the options provided do not include 179, we round it to the nearest option, which is 180.

### Final Answer:
The total number of histone proteins present in chromatin with 20 nucleosomes is approximately **180**.

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