1. DNA Chromosome Structure

2. Chromosomes

3. What are Chromosomes? Linear DNA wrapped around proteins (histones)
When we talk chromosomes, we talk eukaryotic DNA because
Prokaryotic DNA is NAKED unlike
Eukaryotic which is not naked and associated with histones

4. Why does DNA condense into chromosomes?
Size!
(most) Eukaryotic DNA are Gigantic
Chromosomes are easier/ more manageable to move around during mitosis

5. DNA is our genetic material. We may encounter it in the following ways
DNA is our genetic material. We may encounter it in the following ways. First lets talk interphase.
In interphase:
DNA is loose (like spaghetti) form called chromatin.
DNA associated with histones (proteins) in a structure called a nucleosome

6. Why do we refer to the chromatin DNA in interphase as “beads on a string”?
Basic unit of chromatin is Nucleosome connected by DNA strings (linker DNA)

7. Let's look at the nucleosome (page 3 of notes)
8 histone proteins form “octomer core”
Linker DNA connects to next nucleosome
DNA wraps twice around
H1 protein
Which stabilizes histones and holds DNA in place

8. Nucleosomes need to supercoil… Why?
Why? Because it makes DNA more manageable to move during mitosis
Also… DNA is over 3 meters long… coiling it into nucleosomes makes it fit in nucleus but still not very manageable

9. Levels of supercoiling (note page 2)
DNA double Helix (2 nm diameter)---> Nucleosome (10nm)--->Multiple nucleosomes “beads on a string”---> Compacted/coiled nucleosomes (30nm) ---> unreplicated chromosome (200nm)---> replicated chromosome

10. In Mitosis: The DNA is supercoiled and nucleosomes fold onto each other