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Posttranscriptional Modifications

by Georgina Cornwall, PhD
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    00:01 So now, we have the initiation and elongation.

    00:05 And termination, we don’t understand very well in eukaryotes yet.

    00:09 We have also to make some modifications to the messenger RNA transcript in order to make it suitable to leave the nucleus.

    00:20 So we’re going to add a 5’ cap, a poly-A tail to protect it out in the world of the cytosol and we’re also going to cut out sections that don’t code for anything.

    00:35 So first, we bind the 5’ GTP cap.

    00:38 I think about the cap protecting it.

    00:42 The cap, he puts the cap on.

    00:45 Let’s say methylated cap.

    00:46 So it’s a methyl group on there.

    00:47 And the cap is actually put on backwards.

    00:51 It’s a nucleotide because it’s a GTP but some reason, this methylated cap will bind to the 5’ phosphate group with its 5’ phosphate group.

    01:02 So it’s a cap that’s on backwards.

    01:06 He's a pretty cool mRNA.

    01:08 And he needs that on before he can go out into the real word of the cytosol.

    01:13 The other thing that will happen is we will add a poly-A tail.

    01:17 So poly-A tail is actually added by poly-A polymerase, a separate polymerase, who comes along and sort of cuts off the first tail and then polymerize the addition of all these poly-A tails.

    01:30 I imagine the poly-A tail as a another means of protection.

    01:33 So when the mRNA goes out and swims through the cytosol, it doesn’t really but – It’s protecting him from all these other enzymes and PAC-MAN things that are running around in the cytosol trying to chomp at his tail.

    01:47 So he’s protected with 5’ cap and a poly-A tail.

    01:51 He’s good to go.


    About the Lecture

    The lecture Posttranscriptional Modifications by Georgina Cornwall, PhD is from the course Gene Expression.


    Included Quiz Questions

    1. …the addition of 5’ methylated cap, the addition of poly-A tail on 3’ end and splicing of non-coding regions.
    2. …the addition of 3’ methylated cap, the addition of poly-A tail on 5’ end and splicing of non-coding regions.
    3. …the addition of 3’ non-methylated cap, the addition of poly-T tail on 5’ end and splicing of coding regions.
    4. …the addition of 5’ non-methylated cap, the addition of poly-T tail on 3’ end and splicing of coding regions.
    5. …the addition of 5’ non-methylated cap, the addition of poly-U tail on 3’ end and splicing of coding regions.

    Author of lecture Posttranscriptional Modifications

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD


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