In DNA tertiary structure, what is a histone octamer?

Options

A. A complex consisting of eight positively charged histone proteins the aid in the packaging of DNA
B. A complex consisting of eight positively charged histone proteins the aid in the packaging of DNA
C. A complex consisting of eight positively charged histone proteins the aid in the packaging of DNA
D. A complex consisting of eight positively charged histone proteins the aid in the packaging of DNA

Answer

**Step-by-Step Solution:**

1. **Understanding the Context**:
- In the tertiary structure of DNA, chromatin fibers are formed, which are essential for packaging DNA in a compact form within the nucleus of a cell.

2. **Identifying the Histone Octamer**:
- The histone octamer is a specific protein structure that plays a crucial role in the organization of DNA. The term "octamer" indicates that it is composed of eight histone proteins.

3. **Composition of the Histone Octamer**:
- The histone octamer is made up of four different types of histone proteins:
- Two molecules of H2A
- Two molecules of H2B
- Two molecules of H3
- Two molecules of H4
- This totals to eight histone proteins, hence the name "octamer".

4. **Charge Characteristics**:
- Histone proteins are positively charged. This positive charge allows them to interact with the negatively charged DNA, facilitating the wrapping of DNA around the histone octamer.

5. **Role in DNA Packaging**:
- The wrapping of DNA around the histone octamer is crucial for the formation of nucleosomes, which are the fundamental units of chromatin. This organization is essential for the compaction of DNA into chromosomes during cell division.

6. **Linker Histone**:
- In addition to the histone octamer, there is another histone protein known as H1, which acts as a linker histone. It helps in stabilizing the structure of the nucleosome and further compacts the DNA.

7. **Conclusion**:
- Therefore, a histone octamer is a complex of eight positively charged histone proteins that play a vital role in the packaging and organization of DNA into chromatin fibers.