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Eukaryotic Chromosomes – Mitosis

by Georgina Cornwall, PhD
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    00:00 So having had a quick tour of the language of chromosomes, we can now talk about how those chromosomes are composed.

    00:09 So DNA as we know is a long linear strand. And in order for it to function in the cell, it needs to be unwound, and it is in its chromatin form.

    00:21 In order for chromatin to wind up into chromosomes, and pair as sister chromatids as we've seen in our chromosome language, we need to take this DNA and quill it up quite tightly which of course makes it inaccessible.

    00:37 So this is not going to happen until after S phase.

    00:41 So one of the things that's happening during G2, the growth phase 2, is we're beginning to pack up the chromosomes from chromatin.

    00:52 So DNA is our double helix, and we move from DNA and wrap it around a core of four different histone proteins.

    01:01 It goes around there about two and a half times. So this green strand goes around two and a half times around the core of eight histone proteins and it's snapped on by the red guide one other histone protein.

    01:15 So these are like beads on a necklace string.

    01:19 If we were to take those beads on a necklace string and put them into a cylinder and just drop them in one by one, they would stack up on each other. This is our next level of DNA packing.

    01:33 So all of these beads on a string packed together in a tube and then those beads on the string pack together in the tube will then fold and coil upon each other, so we have these looping structures here.

    01:47 And then each of those looping structures will loop again and we call this supercoiling, and then that supercoiling becomes tightly packed and supercoils stack on supercoils to form the whole chromosome, right.

    02:03 So we have here a replicated chromosome. It's composed of two sister chromatids.

    02:08 Both of them have to pack up in this fairly compact means of chromosome packing.


    About the Lecture

    The lecture Eukaryotic Chromosomes – Mitosis by Georgina Cornwall, PhD is from the course Cell Cycle and Cell Division.


    Included Quiz Questions

    1. …a core of eight units histone proteins wrapped with 146 base pairs of superhelical DNA.
    2. …a core of nine units histone proteins wrapped with 146 base pairs of superhelical DNA.
    3. …a core of three units histone proteins wrapped with 146 base pairs of superhelical DNA.
    4. …a core of one histone super protein wrapped with 146 base pairs of superhelical DNA.
    5. …a core of four units histone proteins wrapped with 146 base pairs of superhelical DNA.

    Author of lecture Eukaryotic Chromosomes – Mitosis

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD


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