Chromatin

Chromatin is a mixture of DNA and proteins that forms the chromosomes in humans and other higher organisms. Histone proteins help package DNA into a compact form that can fit inside the nucleus.

• Chromatin = DNA + proteins; histones are key proteins that package DNA to fit in the nucleus.
• At the basic level, DNA wraps around histone proteins to form nucleosomes; nucleosomes are connected by linker DNA (often described as "beads on a string").
• In interphase, tightly packaged chromatin is heterochromatin (genes usually not expressed), while less dense chromatin is euchromatin (genes usually transcribed).

• If you see "DNA wrapped around histones" or "beads on a string" -> <u>nucleosomes/chromatin</u>.
• If a question talks about chromatin being tightly packaged vs less dense in interphase -> <u>heterochromatin vs euchromatin</u>.
• If the stem is really about how DNA is packed to fit in the nucleus -> <u>chromatin (the DNA-protein material)</u> is the key idea.