The two main constituents of a nucleosome are DNA and histone proteins.
Here's a more detailed breakdown:
A nucleosome is the fundamental repeating unit of chromatin, which packages DNA within the nucleus of eukaryotic cells. Think of it as the basic "bead" on a "string" of chromatin.
-
DNA: Approximately 146 base pairs of DNA are wrapped around a histone octamer. This wrapping helps to compact the DNA and regulate gene expression.
-
Histone Proteins: The histone octamer core is composed of eight histone proteins: two copies each of histones H2A, H2B, H3, and H4. These proteins are rich in positively charged amino acids (lysine and arginine), which facilitate their interaction with the negatively charged DNA. Histone H1 is a linker histone that binds to the DNA entering and exiting the nucleosome, helping to stabilize the structure and promote further compaction into higher-order chromatin structures.
| Constituent | Description |
|---|---|
| DNA | ~146 base pairs wound around the histone octamer |
| Histone Proteins | Octamer core (two each of H2A, H2B, H3, and H4) plus linker histone H1 (outside of the core) |
In summary, the nucleosome efficiently packages DNA by winding it around a protein core, enabling the long strands of DNA to fit inside the nucleus and playing a vital role in gene regulation.
