DNA Chromosome Structure

Chromosomes https://www.nature.com/scitable/topicpage/chromosomes-14121320 https://www.youtube.com/watch?v=tsVHWbXqum8 https://www.youtube.com/watch?v=IePMXxQ-KWY http://www.sciencemag.org/news/2016/11/video-how-cram-your-entire-genome-tiny-nucleus https://www.youtube.com/watch?v=0JpOJ4F4984

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

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

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

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)

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

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

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

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