Describe the transitions that occur as nucleosomes are coiled and folded, ultimately forming a chromatid.

Video transcript

Welcome back. Here's our next problem. It says the nucleosome in the blank structure fold and stack to form a helix containing six nucleosome in each turn. So let's look at our answer choices. And the one thing that's a little bit tricky is we know that nucleosome um together strung along like beads on a string, make up the chromatin fiber. So we might be tempted to choose chromatin fiber. However, we're specifically asked about the structure in which these nucleosome are stacked and folded forming a helix. And for that, we want choice c the solenoid and the solenoid is that structure which is condensed chroma chromatin fibers and the nucleus within it are folded and stacked stacked to form a helix. So the reason chromatin fiber isn't our answer is that the chroma chromatin fiber is sort of a lower level of organization below the solenoid. It's a sort of zigzag array of nucleosome where that just consists of the DNA wrapped around the histone proteins. So then that chromatin fiber is condensed into that helical structure to make the solenoid structure. So chromatin condensed into solenoid structures. So chromatin fiber is sort of the next level below of organization below solenoids. Um When we look at choice, a linker DNA, um the linker DNA is part of that solenoid structure, but it's the little pieces of DNA that bind together sequential nucleosome within the solenoid. So to create that W helix, the little bits of bent linker DNA hold together by interacting with the his stones hold together those sequential nucleosome helping to create that solenoid structure. But it's not the solenoid. That's not the name of the structure itself, which is why it's not our correct answer. Choices. And finally, we're down to choice d the his stones which provides that structural support in the chromatin fibers and the complex of histone proteins uh is the protein that the DNA is wound around in those chromosome fibers to create that sort of bead like effect. So not the correct answer since that's not the structure that's formed with this condensed chromatin fiber. So again, the nucleosome in the choice C solenoid structure fold and stack to form a helix containing six nucleosome. In each term. See you in the next video.